Two classes of proteins and mRNAs in Lilium longiflorum L. indentified by human vitronectin probes

Vitronectin (VN) is a substrate adhesion molecule, an extracellular matrix glycoprotein that facilitates cell adhesion and cell movement in animals. We have reported the cross-reactivity of a 55-kD protein in plants with rabbit anti-human VN antibodies and the presence of VN-like sequences in plant genomes using a human VN cDNA probe. We have extended these studies by using human VN riboprobes to detect VN-like mRNAs in lily (Lilium longiflorum L.) and soybean. In both species, two mRNAs were detected. We have also identified a new cross-reactive protein (41 kD) using a different preparation of human VN antiserum. In lily roots five 41-kD isoforms were observed, whereas only three of these isoforms accumulated in leaves. Monospecific antibodies prepared against the plant proteins cross-reacted with the human VN protein and vice versa. We have purified the 41-kD protein using two-dimensional gel electrophoresis, and amino acid composition analysis indicates that it is similar in composition to human VN.

Production of lymphotoxin (LT alpha) and a soluble dimeric form of its receptor using the baculovirus expression system

Human LT alpha and a fusion protein (p60:Fc) comprised of the extracellular domain of the 60 kDa TNF receptor (TNFR60) fused to the Fc portion of human IgG1 were produced in insect cells infected with recombinant baculoviruses. The p60:Fc fusion produced in insect cells accumulates in culture supernatants to levels > 2 mg/l. Purified p60:Fc binds human TNF and LT alpha with high affinity (200-600 pM) and neutralizes TNF cytolytic activity at equimolar stoichiometric concentration. The data show that p60:Fc is an effective ligand-precipitating reagent which recognizes recombinant LT alpha produced in mammalian or insect cells and naturally occurring LT alpha produced in T cells. The levels of human LT alpha produced in baculovirus-infected insect cells is estimated to be approximately 20 mg/l. Insect cell-derived human LT alpha is biologically active in an L929 cytotoxicity assay and is efficiently neutralized by p60:Fc. These data demonstrate that the baculovirus system is useful for overexpressing biologically active LT alpha and p60:Fc and therefore, may be applicable to other oligomeric cytokines and soluble dimeric cytokine receptors.

Specific induction of 80-kDa tumor necrosis factor receptor shedding in T lymphocytes involves the cytoplasmic domain and phosphorylation

The 80-kDa TNFR (TNFR80) expressed by activated human T cells is constitutively phosphorylated and undergoes limited proteolytic cleavage (shedding) at the cell surface releasing a 40-kDa soluble TNF-binding protein. Triggering of activated T cells through the TCR rapidly increased the rate of TNFR80 shedding > 20-fold more than nonstimulated cells, demonstrating that shedding is a specific, inducible process. The protein kinase inhibitor staurosporine inhibited constitutive phosphorylation and blocked inducible shedding of TNFR80, suggesting that phosphorylation may be important for cleavage of the extracellular domain. However, a deletion mutation of the entire cytoplasmic domain of human TNFR80 was shed when expressed in murine L929 cells, albeit relatively poorly compared with full length receptor. This demonstrates that the cytoplasmic domain is important but not essential for cleavage of the extracellular domain of TNFR80. Moreover, a requirement for phosphorylation of proteins other than the receptor was revealed by the finding that staurosporine completely blocked cleavage of the cytoplasmic deletion mutant. Collectively, these results demonstrate that protein phosphorylation is essential and the cytoplasmic domain is important for regulating the inducible production of soluble TNF-binding proteins by activated effector T cells.

Specific induction of 80-kDa tumor necrosis factor receptor shedding in T lymphocytes involves the cytoplasmic domain and phosphorylation

The 80-kDa TNFR (TNFR80) expressed by activated human T cells is constitutively phosphorylated and undergoes limited proteolytic cleavage (shedding) at the cell surface releasing a 40-kDa soluble TNF-binding protein. Triggering of activated T cells through the TCR rapidly increased the rate of TNFR80 shedding > 20-fold more than nonstimulated cells, demonstrating that shedding is a specific, inducible process. The protein kinase inhibitor staurosporine inhibited constitutive phosphorylation and blocked inducible shedding of TNFR80, suggesting that phosphorylation may be important for cleavage of the extracellular domain. However, a deletion mutation of the entire cytoplasmic domain of human TNFR80 was shed when expressed in murine L929 cells, albeit relatively poorly compared with full length receptor. This demonstrates that the cytoplasmic domain is important but not essential for cleavage of the extracellular domain of TNFR80. Moreover, a requirement for phosphorylation of proteins other than the receptor was revealed by the finding that staurosporine completely blocked cleavage of the cytoplasmic deletion mutant. Collectively, these results demonstrate that protein phosphorylation is essential and the cytoplasmic domain is important for regulating the inducible production of soluble TNF-binding proteins by activated effector T cells.

Lymphotoxin beta, a novel member of the TNF family that forms a heteromeric complex with lymphotoxin on the cell surface

The lymphokine tumor necrosis factor (TNF) has a well-defined role as an inducer of inflammatory responses; however, the function of the structurally related molecule lymphotoxin (LT alpha) is unknown. LT alpha is present on the surface of activated T, B, and LAK cells as a complex with a 33 kd glycoprotein, and cloning of the cDNA encoding the associated protein, called lymphotoxin beta (LT beta), revealed it to be a type II membrane protein with significant homology to TNF, LT alpha, and the ligand for the CD40 receptor. The gene for LT beta was found next to the TNF-LT locus in the major histocompatibility complex (MHC), a region of the MHC with possible linkage to autoimmune disease. These observations raise the possibility that a surface LT alpha-LT beta complex may have a specific role in immune regulation distinct from the functions ascribed to TNF.

Expression of surface lymphotoxin and tumor necrosis factor on activated T, B, and natural killer cells

The expression of membrane-associated forms of lymphotoxin (LT) and TNF were examined on cell lines of T, B, and myeloid origin, IL-2 dependent T cell clones, and peripheral blood lymphocytes. Inducible and constitutive patterns of surface LT expression were found on T cells as exemplified by the II-23.D7, a CD4+T cell hybridoma, and HUT-78, a T cell lymphoma. Phorbol ester induced surface LT expression on Ramos, an EBV transformed B cell line, but at a slower rate of appearance when compared to the II-23.D7. Secretion of LT was rapidly inducible by phorbol ester in II-23.D7 and also in HUT-78 but with slower kinetics; surface LT expression continued in both lines after secretion had ceased. Low levels of membrane TNF were transiently induced on II-23.D7 and HUT-78, but none was observed on Ramos. Peripheral blood monocytes and some myeloid tumor lines did not express surface LT. Several T cell clones expressed surface LT after Ag-specific stimulation, and expression persisted several days. Stimulation through the TCR or by IL-2 rapidly induced surface LT on resting peripheral T cells and CD56+ NK cells; pokeweed mitogen activation induced expression on CD20+ B cells. Consistent with previous results, immunoprecipitation with anti-LT mAb showed that LT was complexed with a distinct 33 kDa glycoprotein (p33) on cells that expressed surface LT, whereas secreted LT was not associated with p33. Surface and secreted modes of LT expression by activated T, B, and NK cells suggests that LT can be utilized as either a localized or diffusible mediator in immune responses.

Expression of surface lymphotoxin and tumor necrosis factor on activated T, B, and natural killer cells

The expression of membrane-associated forms of lymphotoxin (LT) and TNF were examined on cell lines of T, B, and myeloid origin, IL-2 dependent T cell clones, and peripheral blood lymphocytes. Inducible and constitutive patterns of surface LT expression were found on T cells as exemplified by the II-23.D7, a CD4+T cell hybridoma, and HUT-78, a T cell lymphoma. Phorbol ester induced surface LT expression on Ramos, an EBV transformed B cell line, but at a slower rate of appearance when compared to the II-23.D7. Secretion of LT was rapidly inducible by phorbol ester in II-23.D7 and also in HUT-78 but with slower kinetics; surface LT expression continued in both lines after secretion had ceased. Low levels of membrane TNF were transiently induced on II-23.D7 and HUT-78, but none was observed on Ramos. Peripheral blood monocytes and some myeloid tumor lines did not express surface LT. Several T cell clones expressed surface LT after Ag-specific stimulation, and expression persisted several days. Stimulation through the TCR or by IL-2 rapidly induced surface LT on resting peripheral T cells and CD56+ NK cells; pokeweed mitogen activation induced expression on CD20+ B cells. Consistent with previous results, immunoprecipitation with anti-LT mAb showed that LT was complexed with a distinct 33 kDa glycoprotein (p33) on cells that expressed surface LT, whereas secreted LT was not associated with p33. Surface and secreted modes of LT expression by activated T, B, and NK cells suggests that LT can be utilized as either a localized or diffusible mediator in immune responses.

Lymphotoxin is expressed as a heteromeric complex with a distinct 33-kDa glycoprotein on the surface of an activated human T cell hybridoma

We characterized the membrane-associated form of lymphotoxin (surface LT) on the activated II-23.D7 T cell hybridoma. Antibodies to rLT precipitated both surface LT and a distinct 33-kDa glycoprotein (p33). Because p33 and surface LT were antigenically unrelated, their coprecipitation suggested a physical association of p33 and surface LT on the membrane. Pulse-chase analysis indicated that LT and p33 associate with each other early in the LT biosynthetic pathway, precluding the possibility that LT is secreted and bound to p33 or a surface receptor. Furthermore, no p33 was associated with the secreted form of LT. Isoelectric focusing of surface LT and p33 under nondenaturing and denaturing conditions confirmed that surface LT and p33 existed as a complex. Treatment of cells with a high concentration of salt or with acid indicated that surface LT is a peripheral membrane protein. Although secreted LT is a homologous trimer, protein cross-linking studies revealed that surface LT existed as a monomer associated with a dimer of p33. Together the results demonstrate a novel mechanism for stable membrane expression of LT by activated T cells.

Tumor necrosis factor (TNF) receptor expression in T lymphocytes. Differential regulation of the type I TNF receptor during activation of resting and effector T cells

The expression of TNF-alpha receptors (TNFR) was examined on a CD4+ T cell hybridoma, transformed T cell lines, CTL clones, and activated T cells from peripheral blood to determine the basis of the immunomodulatory activity of TNF on T cell function. Analyses by ligand cross-linking and competitive binding assays with mAb to the 80-kDa receptor (TNFR-I), demonstrated that the TNFR-I was the predominant receptor expressed on activated CD4+ and CD8+ T cell subsets. However, on T cell leukemic lines, a second, non-TNFR-I binding site was identified, most likely the 55-kDa form (TNFR-II). Additional subsets of T cells were readily distinguished by their expression of TNFR-I and related members of the TNFR gene family (CD40 and CD27). Expression of the TNFR-I was dependent upon the state of T cell activation. Signaling through the TCR for Ag or IL-2R was sufficient to induce TNFR mRNA and protein expression in resting T cells. Multiple sizes of TNFR-I transcripts were detected during T cell activation; however, biosynthetic studies showed these multiple species encode a single protein of 80 kDa. These results, combined with the known ability of TNF to induce IL-2R expression, indicate that TNF and IL-2 form a reciprocating receptor amplification circuit. In contrast, differentiated effector T cells triggered through the TCR or protein kinase C initiated a rapid down-regulation (transmodulation) of the TNFR-I that preceded TNF or lymphotoxin secretion. The mechanism of transmodulation involved proteolytic processing of the mature 80-kDa receptor releasing a soluble 40-kDa fragment. This indicates that a TNF autocrine loop is not likely to form during the response of an effector T cell. Collectively, these results suggest that transcriptional and post-translational modification of the TNFR-I are important control points regulating the expression of this receptor during T cell activation.

Tumor necrosis factor (TNF) receptor expression in T lymphocytes. Differential regulation of the type I TNF receptor during activation of resting and effector T cells

The expression of TNF-alpha receptors (TNFR) was examined on a CD4+ T cell hybridoma, transformed T cell lines, CTL clones, and activated T cells from peripheral blood to determine the basis of the immunomodulatory activity of TNF on T cell function. Analyses by ligand cross-linking and competitive binding assays with mAb to the 80-kDa receptor (TNFR-I), demonstrated that the TNFR-I was the predominant receptor expressed on activated CD4+ and CD8+ T cell subsets. However, on T cell leukemic lines, a second, non-TNFR-I binding site was identified, most likely the 55-kDa form (TNFR-II). Additional subsets of T cells were readily distinguished by their expression of TNFR-I and related members of the TNFR gene family (CD40 and CD27). Expression of the TNFR-I was dependent upon the state of T cell activation. Signaling through the TCR for Ag or IL-2R was sufficient to induce TNFR mRNA and protein expression in resting T cells. Multiple sizes of TNFR-I transcripts were detected during T cell activation; however, biosynthetic studies showed these multiple species encode a single protein of 80 kDa. These results, combined with the known ability of TNF to induce IL-2R expression, indicate that TNF and IL-2 form a reciprocating receptor amplification circuit. In contrast, differentiated effector T cells triggered through the TCR or protein kinase C initiated a rapid down-regulation (transmodulation) of the TNFR-I that preceded TNF or lymphotoxin secretion. The mechanism of transmodulation involved proteolytic processing of the mature 80-kDa receptor releasing a soluble 40-kDa fragment. This indicates that a TNF autocrine loop is not likely to form during the response of an effector T cell. Collectively, these results suggest that transcriptional and post-translational modification of the TNFR-I are important control points regulating the expression of this receptor during T cell activation.

Lymphotoxin and an associated 33-kDa glycoprotein are expressed on the surface of an activated human T cell hybridoma

A human T cell hybridoma, II-23.D7, was induced with phorbol ester to express a surface form of lymphotoxin (LT, TNF-beta) and an associated 33-kDa glycoprotein. The LT epitopes were detected by surface immunofluorescence staining and by immunoprecipitation from radioiodinated or biosynthetically labeled cells with the use of anti-rLT polyclonal and monoclonal antibodies. The epitopes detected by the antibody were related to LT because adsorption of the anti-rLT with PMA-activated II-23.D7 cells resulted in the removal of the neutralizing titer of the anti-rLT antiserum. Immunoprecipitation of surface radioiodinated II-23.D7 cells revealed two bands of 25 kDa and 33 kDa that were specifically precipitated with anti-rLT, but not anti-rTNF antibodies. Enzymatic digestion with glycanases showed both proteins to have N-linked carbohydrate, with O-linked sugar limited to the 25-kDa protein. To determine the biochemical relationship between these proteins, the two LT-like forms were purified from detergent-solubilized II-23.D7 cells by immunoaffinity chromatography. Peptide mapping using CNBr cleavage showed the 25-kDa surface form to be identical to rLT, whereas the 33-kDa protein was different. Biosynthetic labeling studies showed that p33 contained both methionine and cysteine, whereas the p25 contained only methionine. Thus, the surface LT form lacks a leader peptide indicating an anchoring mechanism distinct from that described for membrane TNF. The nature of the attachment of this LT form to the membrane surface is not clear, however, neither TNF receptor binding nor lipid linkages appear to be involved. The accessory protein, p33, may anchor LT to the surface. These findings identify a new characteristic of LT and point toward an additional pathway by which T lymphocytes may mediate cytolytic activity and regulate inflammatory processes.

Lymphotoxin and an associated 33-kDa glycoprotein are expressed on the surface of an activated human T cell hybridoma

A human T cell hybridoma, II-23.D7, was induced with phorbol ester to express a surface form of lymphotoxin (LT, TNF-beta) and an associated 33-kDa glycoprotein. The LT epitopes were detected by surface immunofluorescence staining and by immunoprecipitation from radioiodinated or biosynthetically labeled cells with the use of anti-rLT polyclonal and monoclonal antibodies. The epitopes detected by the antibody were related to LT because adsorption of the anti-rLT with PMA-activated II-23.D7 cells resulted in the removal of the neutralizing titer of the anti-rLT antiserum. Immunoprecipitation of surface radioiodinated II-23.D7 cells revealed two bands of 25 kDa and 33 kDa that were specifically precipitated with anti-rLT, but not anti-rTNF antibodies. Enzymatic digestion with glycanases showed both proteins to have N-linked carbohydrate, with O-linked sugar limited to the 25-kDa protein. To determine the biochemical relationship between these proteins, the two LT-like forms were purified from detergent-solubilized II-23.D7 cells by immunoaffinity chromatography. Peptide mapping using CNBr cleavage showed the 25-kDa surface form to be identical to rLT, whereas the 33-kDa protein was different. Biosynthetic labeling studies showed that p33 contained both methionine and cysteine, whereas the p25 contained only methionine. Thus, the surface LT form lacks a leader peptide indicating an anchoring mechanism distinct from that described for membrane TNF. The nature of the attachment of this LT form to the membrane surface is not clear, however, neither TNF receptor binding nor lipid linkages appear to be involved. The accessory protein, p33, may anchor LT to the surface. These findings identify a new characteristic of LT and point toward an additional pathway by which T lymphocytes may mediate cytolytic activity and regulate inflammatory processes.

Adenovirus E3 14.7K protein functions in the absence of other adenovirus proteins to protect transfected cells from tumor necrosis factor cytolysis

A 14,700-kDa protein (14.7K) encoded by the E3 region of adenovirus has been shown to protect adenovirus-infected mouse C3HA cells from lysis by tumor necrosis factor (TNF) (L. R. Gooding, L. W. Elmore, A. E. Tollefson, H. A. Brady, and W. S. M. Wold, Cell 53:341-346, 1988). These infected cells are sensitized to TNF by expression of the adenovirus E1A proteins (P. Duerksen-Hughes, W. S. M. Wold, and L. R. Gooding, J. Immunol. 143:4193-4200, 1989). In this study we show that 14.7K suppresses TNF cytolysis independently of adenovirus infection. Mouse C3HA and C127 cells were transfected with the 14.7K gene controlled by the mouse metallothionein promoter, and permanent 14.7K-expressing cell lines were tested for sensitivity to TNF cytolysis. Transfected cells which were sensitized to TNF either by inhibitors of protein synthesis, microfilament-destabilizing agents, or adenovirus infection were found to be resistant to TNF cytolysis. Two monoclonal antibodies were isolated and used to quantitate 14.7K in transfected and infected cells. Enzyme-linked immunosorbent assay (ELISA) analysis with these monoclonal antibodies and 14.7K immunoblots showed that 14.7K expression can be induced with cadmium in C3HA and C127 transfectants. The 14.7K induction correlated with a dose-dependent decrease in sensitivity to TNF cytotoxicity. The 14.7K protein does not substantially alter cell surface TNF receptor numbers or affinity on C3HA mouse fibroblasts, as determined by Scatchard analysis of 125I-TNF binding. The 14.7K protein also does not alter TNF signal transduction in general, because TNF induction of cell surface class I major histocompatibility complex molecules on 14.7K transfectants was unmodified. Our findings indicate that the adenovirus 14.7K protein functions as a specific inhibitor of TNF cytolysis in the absence of other adenovirus proteins and thus is a unique tool to study the mechanism of TNF cytotoxicity.

Inhibitors of ADP-ribose polymerase decrease the resistance of HER2/neu-expressing cancer cells to the cytotoxic effects of tumor necrosis factor

Four human ovarian and breast tumor lines expressing the HER2/neu oncogene were resistant to the cytotoxic and DNA-degradative activity of TNF. The resistance was not associated with altered TNF receptor function because Scatchard analysis of 125I-rTNF binding to HER2/neu-expressing target cells revealed receptors with normal binding parameters. Furthermore, the TNF receptors on the resistant lines were capable of signal transduction as evidence by the induction of ADP-ribose polymerase activity and MHC expression. TNF resistance was not reversed by coincubation with drugs that interrupted the glutathione redox cycle. In addition, although coincubation of HER2/neu-expressing targets with cycloheximide resulted in significant TNF-induced lysis, when compared to HER2/neu-nonexpressing targets similarly treated with cycloheximide, a significant relative resistance was still present. To investigate the role of ADP-ribosylation in the resistance of these targets, we used nontoxic concentrations of two inhibitors of ADP-ribose polymerase, 3-aminobenzamide, and nicotinamide. Both inhibitors completely reversed the resistance of HER2/neu-expressing targets to TNF-mediated cytotoxicity and DNA injury in a concentration-dependent fashion. These inhibitors of ADP-ribose polymerase did not act by down-regulating expression of HER2/neu oncogenes. In contrast, aminobenzamide and nicotinamide significantly diminished TNF-induced cytotoxicity of L929 targets. These data suggest that the activity of ADP-ribose polymerase may play a pivotal role in determining the fate of the target cell during exposure to TNF.

Inhibitors of ADP-ribose polymerase decrease the resistance of HER2/neu-expressing cancer cells to the cytotoxic effects of tumor necrosis factor

Four human ovarian and breast tumor lines expressing the HER2/neu oncogene were resistant to the cytotoxic and DNA-degradative activity of TNF. The resistance was not associated with altered TNF receptor function because Scatchard analysis of 125I-rTNF binding to HER2/neu-expressing target cells revealed receptors with normal binding parameters. Furthermore, the TNF receptors on the resistant lines were capable of signal transduction as evidence by the induction of ADP-ribose polymerase activity and MHC expression. TNF resistance was not reversed by coincubation with drugs that interrupted the glutathione redox cycle. In addition, although coincubation of HER2/neu-expressing targets with cycloheximide resulted in significant TNF-induced lysis, when compared to HER2/neu-nonexpressing targets similarly treated with cycloheximide, a significant relative resistance was still present. To investigate the role of ADP-ribosylation in the resistance of these targets, we used nontoxic concentrations of two inhibitors of ADP-ribose polymerase, 3-aminobenzamide, and nicotinamide. Both inhibitors completely reversed the resistance of HER2/neu-expressing targets to TNF-mediated cytotoxicity and DNA injury in a concentration-dependent fashion. These inhibitors of ADP-ribose polymerase did not act by down-regulating expression of HER2/neu oncogenes. In contrast, aminobenzamide and nicotinamide significantly diminished TNF-induced cytotoxicity of L929 targets. These data suggest that the activity of ADP-ribose polymerase may play a pivotal role in determining the fate of the target cell during exposure to TNF.

Induction of the heat shock response protects cells from lysis by tumor necrosis factor

A minority of transformed cell lines are directly susceptible to lysis by TNF, whereas many cells can be made sensitive to TNF by treatment with inhibitors of protein synthesis. Other groups have shown that exposure to TNF induces in many cells a transcription/translation dependent response that protects the cell from TNF lysis. Heat shock proteins are involved in protecting cells from the lethal affects of heat and other metabolic poisons. In this report, we test the possibility that heat shock proteins are also involved in protecting cells from lysis by TNF. We find that after induction of the cellular heat shock response by either heat or arsenite treatment, both spontaneously TNF-sensitive cells and those cells made sensitive by inhibition of protein synthesis are nearly completely protected from TNF cytolysis. The heat-treated cells retained most of their capacity to bind TNF, suggesting that heat shock functions at a postreceptor binding phase of the lytic process. Mouse C3HA fibroblasts are also made sensitive to TNF lysis by treatment with cytochalasin E. We have previously found that elicitation of the cell's TNF-protective response by exposure to TNF suppresses killing of C3HA by subsequent treatment with TNF plus cytochalasin E. In contrast, we report here that induction of the heat shock response did not provide significant protection to C3HA from killing by TNF in the presence of cytochalasin E. Thus, although induction of heat shock proteins does protect cells from TNF, they appear to act by a mechanism distinct from that elicited by TNF itself.

Induction of the heat shock response protects cells from lysis by tumor necrosis factor

A minority of transformed cell lines are directly susceptible to lysis by TNF, whereas many cells can be made sensitive to TNF by treatment with inhibitors of protein synthesis. Other groups have shown that exposure to TNF induces in many cells a transcription/translation dependent response that protects the cell from TNF lysis. Heat shock proteins are involved in protecting cells from the lethal affects of heat and other metabolic poisons. In this report, we test the possibility that heat shock proteins are also involved in protecting cells from lysis by TNF. We find that after induction of the cellular heat shock response by either heat or arsenite treatment, both spontaneously TNF-sensitive cells and those cells made sensitive by inhibition of protein synthesis are nearly completely protected from TNF cytolysis. The heat-treated cells retained most of their capacity to bind TNF, suggesting that heat shock functions at a postreceptor binding phase of the lytic process. Mouse C3HA fibroblasts are also made sensitive to TNF lysis by treatment with cytochalasin E. We have previously found that elicitation of the cell's TNF-protective response by exposure to TNF suppresses killing of C3HA by subsequent treatment with TNF plus cytochalasin E. In contrast, we report here that induction of the heat shock response did not provide significant protection to C3HA from killing by TNF in the presence of cytochalasin E. Thus, although induction of heat shock proteins does protect cells from TNF, they appear to act by a mechanism distinct from that elicited by TNF itself.

Double-negative (CD4- CD8-) T cells with an alpha/beta T cell receptor. Non-MHC-restricted cytolytic activity and lymphokine production

T cell lines with a novel phenotype (CD3+ TCR-alpha/beta+ CD4- CD8-) were developed from the peripheral blood of a patient with a combined immunodeficiency and tissue injury resembling graft-vs-host disease. One of these IL-2-dependent T cell lines demonstrated non-MHC-restricted cytolytic function against tumor targets, syngeneic and allogeneic fibroblasts, and PHA blasts from allogeneic donors. The other cell line only became cytotoxic in the presence of lectin or anti-CD3 antibody. The two cell lines also differed in their expression of the T-200 gene products CD45RO (gp180) and CD45RA (gp220). Both cell lines produced tumor necrosis factor-alpha and -beta and IFN-gamma activity when activated with mitogens or PMA and IL-1. The in vitro functions of these T-cell lines suggest a potential role for alpha/beta double-negative T lymphocytes in tissue injury resembling graft-vs-host disease.

Double-negative (CD4- CD8-) T cells with an alpha/beta T cell receptor. Non-MHC-restricted cytolytic activity and lymphokine production

T cell lines with a novel phenotype (CD3+ TCR-alpha/beta+ CD4- CD8-) were developed from the peripheral blood of a patient with a combined immunodeficiency and tissue injury resembling graft-vs-host disease. One of these IL-2-dependent T cell lines demonstrated non-MHC-restricted cytolytic function against tumor targets, syngeneic and allogeneic fibroblasts, and PHA blasts from allogeneic donors. The other cell line only became cytotoxic in the presence of lectin or anti-CD3 antibody. The two cell lines also differed in their expression of the T-200 gene products CD45RO (gp180) and CD45RA (gp220). Both cell lines produced tumor necrosis factor-alpha and -beta and IFN-gamma activity when activated with mitogens or PMA and IL-1. The in vitro functions of these T-cell lines suggest a potential role for alpha/beta double-negative T lymphocytes in tissue injury resembling graft-vs-host disease.

Characterization of the receptor for tumor necrosis factor (TNF) and lymphotoxin (LT) on human T lymphocytes. TNF and LT differ in their receptor binding properties and the induction of MHC class I proteins on a human CD4+ T cell hybridoma

TNF-alpha and lymphotoxin (LT or TNF-beta) are structurally related cytokines that share several proinflammatory and immunomodulatory activities. The shared biologic activities of TNF and LT have been attributed to their binding to a common cell surface receptor(s). We observed that rTNF enhanced the expression of MHC class I proteins on the human T cell hybridoma, II-23.D7, however LT was largely unable to regulate MHC expression. To determine the molecular basis of this disparity between LT and TNF the receptor binding characteristics of rTNF and rLT were investigated by direct and competitive radioligand assays on the II-23.D7 T hybridoma, and for comparison, anti-CD3 activated human T lymphocytes. Specific 125I-rTNF binding to the II-23.D7 line revealed a single class of sites with a Kd = 175 pM and 3000 sites/cell; anti-CD3 activated T cells exhibited specific TNF binding with similar properties. The relationship of receptor occupancy to the induction of MHC class I Ag yielded a hyperbolic curve indicating a complex relationship between rTNF binding and biologic response. LT appeared to function like a partial agonist in that rLT was 10- to 20-fold less effective than rTNF in competitively inhibiting 125I-rTNF binding on the II-23.D7 line. Scatchard type analysis revealed a single class of low affinity binding sites for 125I-rLT. No differences in the competitive binding activity of rTNF and rLT were observed on the anti-CD3-activated T cells. Receptors for rTNF and rLT were immunoprecipitated from the II-23.D7 and activated T cells with anticytokine antibodies after cross-linking of radioiodinated rTNF or rLT to intact cells by using chemical cross-linking reagents. Analysis of the cross-linked adducts by SDS-PAGE and autoradiography indicated a major adduct of 92 kDa for rTNF and 104 kDa for rLT. Enzymatic digestion with neuraminidase or V8 protease revealed a unique structure to these adducts consistent with the cross-linking of a single chain of cytokine to a cell surface glycoprotein. rTNF inhibited the formation of the 104-kDa adduct formed with 125I-rLT on the II-23.D7 line, indicating these two cytokines bind to the same receptor of approximately 80 kDa. These results suggest that the disparate activities of LT and TNF to induce MHC class I proteins on the II-23.D7 cells are, in part, associated with a modified state of a common receptor.

Characterization of the receptor for tumor necrosis factor (TNF) and lymphotoxin (LT) on human T lymphocytes. TNF and LT differ in their receptor binding properties and the induction of MHC class I proteins on a human CD4+ T cell hybridoma

TNF-alpha and lymphotoxin (LT or TNF-beta) are structurally related cytokines that share several proinflammatory and immunomodulatory activities. The shared biologic activities of TNF and LT have been attributed to their binding to a common cell surface receptor(s). We observed that rTNF enhanced the expression of MHC class I proteins on the human T cell hybridoma, II-23.D7, however LT was largely unable to regulate MHC expression. To determine the molecular basis of this disparity between LT and TNF the receptor binding characteristics of rTNF and rLT were investigated by direct and competitive radioligand assays on the II-23.D7 T hybridoma, and for comparison, anti-CD3 activated human T lymphocytes. Specific 125I-rTNF binding to the II-23.D7 line revealed a single class of sites with a Kd = 175 pM and 3000 sites/cell; anti-CD3 activated T cells exhibited specific TNF binding with similar properties. The relationship of receptor occupancy to the induction of MHC class I Ag yielded a hyperbolic curve indicating a complex relationship between rTNF binding and biologic response. LT appeared to function like a partial agonist in that rLT was 10- to 20-fold less effective than rTNF in competitively inhibiting 125I-rTNF binding on the II-23.D7 line. Scatchard type analysis revealed a single class of low affinity binding sites for 125I-rLT. No differences in the competitive binding activity of rTNF and rLT were observed on the anti-CD3-activated T cells. Receptors for rTNF and rLT were immunoprecipitated from the II-23.D7 and activated T cells with anticytokine antibodies after cross-linking of radioiodinated rTNF or rLT to intact cells by using chemical cross-linking reagents. Analysis of the cross-linked adducts by SDS-PAGE and autoradiography indicated a major adduct of 92 kDa for rTNF and 104 kDa for rLT. Enzymatic digestion with neuraminidase or V8 protease revealed a unique structure to these adducts consistent with the cross-linking of a single chain of cytokine to a cell surface glycoprotein. rTNF inhibited the formation of the 104-kDa adduct formed with 125I-rLT on the II-23.D7 line, indicating these two cytokines bind to the same receptor of approximately 80 kDa. These results suggest that the disparate activities of LT and TNF to induce MHC class I proteins on the II-23.D7 cells are, in part, associated with a modified state of a common receptor.

Enhanced cytotoxicity in the rheumatoid joint

The cytotoxic cytokines, tumor necrosis factor-alpha or cachectin and lymphotoxin (LT), are mediators of bone resorption and of inflammation and may have relevance in rheumatoid arthritis. Using mononuclear cells (MC) isolated from matched peripheral blood (PB) and synovial fluid (SF) of 13 patients with rheumatoid arthritis, we examined the generation of cytotoxic activity in a bioassay capable of detecting both TNF and LT. Synovial fluid mononuclear cells (MC) released significantly more cytotoxic activity than did matched PBMC, both spontaneously and following activation with phytohemagglutinin P (PHA). When PB and SFMC were stimulated with the combination of PHA plus phorbol-12-myristate acetate (PMA), the resulting culture supernatants possessed comparable cytotoxic activity. Neutralization studies employing anti-cytokine antibodies indicated that TNF represented 43 and 59% of the cytotoxic activity in the PHA plus PMA-induced culture supernatants from PB and SF, respectively. Since no inhibition was noted with antibodies to LT, the nature of the remaining approximately 50% of the cytotoxic activity was not determined. In PB and SF culture supernatants, obtained both spontaneously and following PHA activation, the concentration of TNF measured by ELISA significantly correlated with the level of cytotoxicity. As with the cytotoxic activity, the concentration of TNF was greater in the PHA-stimulated supernatants from SF than from PB. These observations suggest that TNF in the SF may contribute to the inflammation and bone destruction observed in rheumatoid arthritis.

Protection from O,O,S-trimethyl phosphorothioate-induced immune suppression

Acute administration of nontoxic doses of an impurity in technical malathion, O,O,S-trimethyl phosphorothioate (OOS-TMP), was able to block the in vitro generation of cytotoxic T lymphocytes (CTL) to alloantigen and antibody-secreting cells (Ab) to sheep red blood cells (SRBC). The effects of an antagonist of the delayed toxicity and lung damage of OOS-TMP, O,O,O-trimethyl phosphorothionate (OOO-TMP), and pretreatment of tolerance-inducing doses of OOS-TMP on OOS-TMP-induced immune suppression were examined. Treatment groups included (A) acute administration of OOO-TMP, (B) coadministration of OOO-TMP with OOS-TMP (at concentrations which have been shown previously to block lung toxicity). (C) repeated (4 x on consecutive days) administration of OOS-TMP (which was shown previously to block a lung toxicity which occurs following a challenge with OOS-TMP) and (D) repeated administration of OOS-TMP followed by a challenge dose of OOS-TMP 24 h before death. There was no change in lymphoid organ size following any of these treatments. However, splenocytes from animals that were exposed to treatment regimes A, B and D had significantly elevated proliferative responses to mitogens concanavalin A (ConA) and lipopolysaccharide (LPS). The ability of splenocytes to generate an Ab response to SRBC was significantly elevated following treatment regime A and at the lower dose in treatment regime D. All other treatment protocols did not alter this immune parameter. There was no difference in the ability of splenocytes to generate a CTL response following these treatment regimes. In conclusion, the degree of protection from immune suppression by these treatments which have been shown to protect against lung toxicity varied with the sensitivity of the immune parameters to suppression by acute administration of OOS-TMP.

Effects of subacute administration of O,S,S-trimethyl phosphorodithioate on cellular and humoral immune response systems

The effects of 14-day treatment with low doses of O,S,S-trimethyl phosphorodithioate (OSS-TMP), an impurity in technical malathion, on the generation of cell-mediated and humoral immune responses were examined in female C57BL/6 mice. At a dose of 2.0 mg/kg per day OSS-TMP, the generation of antibody-secreting cells to sheep red blood cells, the generation of cytotoxic T lymphocytes (CTL) to alloantigen and the production of Interleukin-2 were elevated approximately 2-3 fold, while no changes were observed in the proliferative responses to the polyclonal activators, Concanavalin A, lipopolysaccharide, or phytohemagglutinin. In contrast, at 5.0 mg/kg per day OSS-TMP, both the CTL and specific antibody responses were suppressed, while all other immune parameters examined were unchanged. Data from cell separation and reconstitution experiments indicated that both T and B lymphocytes were affected by these treatment regimes. These data suggest that long-term exposure to low doses of OSS-TMP may enhance the ability of an animal to generate an immune response while higher doses of OSS-TMP may suppress the generation of an immune response.

Cytotoxicity mediated by tumor necrosis factor in variant subclones of the ME-180 cervical carcinoma line: modulation by specific inhibitors of DNA topoisomerase II

The mechanism of tumor necrosis factor (TNF)-induced cytotoxicity has been investigated using two clonal variants of the ME-180 human cervical carcinoma cell line. The clonal lines were characterized with respect to their expression of TNF receptors, kinetics of cell death, and their ability to communicate intercellularly through gap junctions. The ME-180.4 and ME-180.8 clones were identified by their relative sensitivity to TNF induced lysis in a 24-h assay. The dose of TNF required to kill 50% of the target cells was 60 pM for the sensitive ME-180.4 and 2.5 nM for the ME-180.8. However, when assay times were extended, the dose response for both clones was the same, indicating that a difference in the kinetics of cell death and not absolute TNF sensitivity existed between the ME-180.4 and ME-180.8 clones. Both clones were gap junction deficient as judged by their inability to transfer Lucifer yellow or 6-carboxyfluorescein, a characteristic phenotype of cells sensitive to cytotoxicity by TNF. The level of surface receptor expressed on these clones was nearly identical with a Kd = 0.3 nM and 5,000 binding sites per cell. Measurement of the kinetics of cell death revealed that the time between the addition of TNF and the onset of observed cell death (induction phase) was much shorter for the ME-180.4 (32-55 h) than for the resistant ME-180.8 (55-80 h). Mitomycin C, a DNA alkylating agent, significantly reduced the length of the induction phase for both clones, although the kinetic difference between the clones remained unchanged. Two epipodophyllotoxins, VP-16 and VM-26, which specifically inhibit the rejoining activity of DNA topoisomerase II, showed a 10-100-fold synergistic effect when combined with TNF as shown by isobologram analysis. VM-26 when added to the resistant ME-180.8 clones decreased the length of induction phase and abolished the kinetic difference observed with the ME-180.4 clone. These results indicate that the variance in the TNF response of these two clones was closely associated with DNA topoisomerase II, and suggest that this enzyme may play an important role in TNF mediated cytotoxicity.

Cytotoxicity by tumor necrosis factor is linked with the cell cycle but does not require DNA synthesis

The relationship between the kinetics of cell death induced by TNF and the cell cycle in L929.10 target cells was investigated by comparison of growing, asynchronous cells with target cells synchronized at G1/S using a double thymidine block. The induction phase of lysis, the time following TNF addition but before loss of cell viability, was shortened in asynchronous cells by increasing the level of saturation of the TNF receptor. However, in synchronized target cells, the length of the induction phase showed no dependence on receptor occupancy. Almost all cell death occurred within a 3 hr period 4-7 hr after the addition of TNF regardless of the concentration of TNF. Target cell lysis in synchronized cells was concomitant with mitosis as verified by flow cytometry and DNA staining with propidium iodide. The narrow window of cytotoxicity was not due to cell cycle-related changes in the expression of the TNF receptor as measured by [125I]TNF binding. Treatment with TNF did not accelerate or retard the progression of cells through S and G2/M nor did target cells accumulate at G2/M. When the kinetic experiments were repeated in the presence of 2 mM thymidine, TNF-treated cells died with identical dose and kinetic responses as those in which the thymidine block had been removed. Under these conditions, flow cytometric analysis revealed that DNA synthesis remained inhibited. These results suggest that TNF-induced cytotoxicity is linked to cell cycle-associated processes and that TNF is capable of overriding the normal cellular controls that coordinately link the DNA replicative cycle with the mitotic cycle. In the L929.10 target cell, TNF may induce a fatal mitosis-linked event.

Effects of acute administration of O,S,S-trimethyl phosphorodithioate on the generation of cellular and humoral immune responses following in vitro stimulation

The time course of immune modulation induced by acute treatment with O,S,S-trimethyl phosphorodithioate (OSS-TMP), an impurity in technical formulations of malathion, was examined in female C57BL/6 mice. The immune parameters studied included the generation of cytotoxic T lymphocytes (CTL) to alloantigen (H-2 incompatible) and antibody secreting cells to sheep red blood cells, proliferative response to the mitogens, and interleukin-2 (IL-2) production. Acute administration of the non-toxic doses of OSS-TMP, i.e. 20 or 40 mg/kg, led to an elevation in the generation of a CTL response on day 1 or 7, respectively. At 20 mg/kg OSS-TMP, the antibody response was elevated at day 3. However, at a dose of 40 mg/kg OSS-TMP, the antibody response was suppressed at day 1 following treatment. Following acute administration of 60 or 80 mg/kg OSS-TMP, the generation of an antibody and CTL responses was suppressed at all time points tested with 1 exception. One day following treatment at a dose of 60 mg/kg OSS-TMP, there was no change in the CTL response. At day 7 following treatment, the mitogenic responses to lipopolysaccharide and phytohemagglutinin were elevated at all doses of OSS-TMP administered. At this time point, however, the proliferative response to Concanavalin A was elevated in a dose dependent manner. IL-2 production was suppressed following acute administration of 60 or 80 mg/kg OSS-TMP at all time points tested and at all doses tested on day 5 following treatment. These data indicate that OSS-TMP, unlike its congener, O,O,S-trimethyl phosphorothioate, enhances the generation of humoral and cell mediated immune responses of C57BL/6 mice following administration of non-toxic doses.

Inhibition of cytotoxic T lymphocyte and natural killer cell-mediated lysis by O,S,S,-trimethyl phosphorodithioate is at an early postrecognition step

O,S,S,-Trimethyl phosphorodithioate (OSS-TMP), an organophosphate esterase inhibitor, has been shown to block the effector phase of the cytolytic reaction mediated by murine and human cytotoxic T lymphocytes (CTL) and human natural killer cells. The murine interleukin 2-dependent CTLL-1 (anti-Iad) clone was used to determine the phase of the cytolytic pathway inhibited by OSS-TMP. Pretreatment of the CTL or target cell with OSS-TMP was not effective at blocking lysis; however, inhibition of lysis was achieved if the reaction was carried out in the continuous presence of OSS-TMP (IC50 = 55 microM) or when CTL-target conjugates were performed and incubated with OSS-TMP (IC50 = 640 microM). Two structural analogues of OSS-TMP were unable to inhibit CTL-mediated lysis. In contrast to OSS-TMP, N-alpha-p-tosyl-L-lysine chloromethylketone required only a 5-min preincubation with the CTL to inhibit lysis. OSS-TMP did not block recognition-adhesion step(s) of the reaction since the ability to form conjugates was not impaired; however, the lytic efficiency of individual CTL-target pairs were blocked. OSS-TMP did not appear to be an inhibitor of the major granule-associated protease that cleaves the substrate, N-alpha-benzyloxycarbonyl-L-lysine thiobenzylester. Ca2+ pulse and kinetic experiments indicated that the OSS-TMP-sensitive site was at a pre-Ca2+-dependent phase but after recognition-adhesion. Human CTL and natural killer cell activity was also inhibited by OSS-TMP, suggesting the presence of a common site of action among these cytolytic systems. The results indicate that OSS-TMP may be a useful reagent in characterizing the early post-recognition events in the cytolytic pathway of CTL and natural killer effector cells.

Inhibition of cytotoxic T lymphocyte and natural killer cell-mediated lysis by O,S,S,-trimethyl phosphorodithioate is at an early postrecognition step

O,S,S,-Trimethyl phosphorodithioate (OSS-TMP), an organophosphate esterase inhibitor, has been shown to block the effector phase of the cytolytic reaction mediated by murine and human cytotoxic T lymphocytes (CTL) and human natural killer cells. The murine interleukin 2-dependent CTLL-1 (anti-Iad) clone was used to determine the phase of the cytolytic pathway inhibited by OSS-TMP. Pretreatment of the CTL or target cell with OSS-TMP was not effective at blocking lysis; however, inhibition of lysis was achieved if the reaction was carried out in the continuous presence of OSS-TMP (IC50 = 55 microM) or when CTL-target conjugates were performed and incubated with OSS-TMP (IC50 = 640 microM). Two structural analogues of OSS-TMP were unable to inhibit CTL-mediated lysis. In contrast to OSS-TMP, N-alpha-p-tosyl-L-lysine chloromethylketone required only a 5-min preincubation with the CTL to inhibit lysis. OSS-TMP did not block recognition-adhesion step(s) of the reaction since the ability to form conjugates was not impaired; however, the lytic efficiency of individual CTL-target pairs were blocked. OSS-TMP did not appear to be an inhibitor of the major granule-associated protease that cleaves the substrate, N-alpha-benzyloxycarbonyl-L-lysine thiobenzylester. Ca2+ pulse and kinetic experiments indicated that the OSS-TMP-sensitive site was at a pre-Ca2+-dependent phase but after recognition-adhesion. Human CTL and natural killer cell activity was also inhibited by OSS-TMP, suggesting the presence of a common site of action among these cytolytic systems. The results indicate that OSS-TMP may be a useful reagent in characterizing the early post-recognition events in the cytolytic pathway of CTL and natural killer effector cells.

Purification and characterization of a pectin lyase produced by Pseudomonas fluorescens W51

A pectin lyase (PNL; EC 4.2.2.10) was isolated from culture filtrates of Pseudomonas fluorescens W51 and purified to apparent homogeneity. The enzyme catalyzed a random eliminative cleavage of pectin but not sodium polypectate, and it macerated plant tissue. The Mr of the PNL on sodium dodecyl sulfate-polyacrylamide gels was 32,000 +/- 1,000, and the isoelectric point was 9.4 as determined by isoelectric focusing. The enzyme was constitutively produced, since the highest yields were obtained when glycerol was used as a sole carbon source, and addition of pectin to the medium did not increase its production. Antibodies against purified PNL reacted in Western blots (immunoblots) with a pectate lyase (PLb) produced by Erwinia chrysanthemi EC16. The PNL appeared to be the only factor secreted into the culture medium by P. fluorescens W51 which macerated plant tissue and is probably involved in the soft rot disease caused by the bacterium.

Resistance to the cytolytic action of lymphotoxin and tumor necrosis factor coincides with the presence of gap junctions uniting target cells

The resistance of target cells to the cytolytic action of lymphotoxin (LT) and recombinant tumor necrosis factor (rTNF) has been investigated by using clonally derived cell lines with defined gap junction-mediated, intercellular communication properties. Gap junction-competent Chinese hamster ovary cells are normally insensitive to the action of LT/TNF. However, treatment with 12-o-tetradecanoylphorbol-13-acetate, which promotes the loss of gap junctions, or culturing at low cell density to reduce intercellular contacts, significantly increased their sensitivity to LT/TNF. The LT/TNF-sensitive murine CL-1D and L929 cell lines, which in normal culture conditions are unable to form gap junctions, were not changed in their susceptibility to LT/TNF after treatment with phorbol ester or low culture density. However, the formation of gap junctions by CL-1D can be promoted by treatment with 8-bromo-cyclic adenosine monophosphate (1 mM), and this treatment completely suppressed the ability of LT and rTNF to kill CL-1D. Additionally, the LA25-normal rat kidney cell line, which is infected with a temperature-sensitive mutant of Rous sarcoma virus (LA25), is gap junction-competent and resistant to the effects of LT at the restrictive temperature (39 degrees C). However, when shifted to the permissive temperature (33 degrees C), LA25-normal rat kidney cells express the pp60v-src viral gene product, lose their ability to form gap junctions, and become sensitive to the lytic activity of LT. The results demonstrate that the expression of the retroviral pp60v-src, a tyrosine protein kinase, is sufficient to render cells susceptible to the lytic effects of LT and rTNF. Collectively, these experiments demonstrate a strong correlation between the resistance of target cells to the action of LT/TNF and their ability to cooperate metabolically through gap junctions. The results do not completely exclude the possibility that other mechanisms, such as LT receptor modulation, are also occurring under these experimental conditions. These data also suggest that a possible physiologic function of the stable cytotoxic lymphokines is to induce cytolysis/cytostasis of cells that have lost gap junctional contact, such as those in the process of mitosis or metastasis that have separated from the main tissue mass.

Resistance to the cytolytic action of lymphotoxin and tumor necrosis factor coincides with the presence of gap junctions uniting target cells

The resistance of target cells to the cytolytic action of lymphotoxin (LT) and recombinant tumor necrosis factor (rTNF) has been investigated by using clonally derived cell lines with defined gap junction-mediated, intercellular communication properties. Gap junction-competent Chinese hamster ovary cells are normally insensitive to the action of LT/TNF. However, treatment with 12-o-tetradecanoylphorbol-13-acetate, which promotes the loss of gap junctions, or culturing at low cell density to reduce intercellular contacts, significantly increased their sensitivity to LT/TNF. The LT/TNF-sensitive murine CL-1D and L929 cell lines, which in normal culture conditions are unable to form gap junctions, were not changed in their susceptibility to LT/TNF after treatment with phorbol ester or low culture density. However, the formation of gap junctions by CL-1D can be promoted by treatment with 8-bromo-cyclic adenosine monophosphate (1 mM), and this treatment completely suppressed the ability of LT and rTNF to kill CL-1D. Additionally, the LA25-normal rat kidney cell line, which is infected with a temperature-sensitive mutant of Rous sarcoma virus (LA25), is gap junction-competent and resistant to the effects of LT at the restrictive temperature (39 degrees C). However, when shifted to the permissive temperature (33 degrees C), LA25-normal rat kidney cells express the pp60v-src viral gene product, lose their ability to form gap junctions, and become sensitive to the lytic activity of LT. The results demonstrate that the expression of the retroviral pp60v-src, a tyrosine protein kinase, is sufficient to render cells susceptible to the lytic effects of LT and rTNF. Collectively, these experiments demonstrate a strong correlation between the resistance of target cells to the action of LT/TNF and their ability to cooperate metabolically through gap junctions. The results do not completely exclude the possibility that other mechanisms, such as LT receptor modulation, are also occurring under these experimental conditions. These data also suggest that a possible physiologic function of the stable cytotoxic lymphokines is to induce cytolysis/cytostasis of cells that have lost gap junctional contact, such as those in the process of mitosis or metastasis that have separated from the main tissue mass.

Effects of O,S,S-trimethyl phosphorodithioate on immune function

The effect of acute administration of 20-80 mg/kg O,S,S-trimethyl phosphorodithioate (OSS-TMP) to C57BL/6 female mice on the murine immune system was determined. The parameters examined to evaluate overt toxicity of the compound included body weight, plasma cholinesterase levels, splenic nucleated cell number and thymic weight and nucleated cell number. Acute administration of 60 or 80 mg/kg OSS-TMP led to a 75 or 63% decrease, respectively, in plasma cholinesterase levels and a decrease in thymic size. At a dose of 80 mg/kg OSS-TMP, the animals also exhibited some lethargy and body weight loss. Below 60 mg/kg OSS-TMP, no overt toxic manifestations were observed. These studies were carried further to determine the effect of OSS-TMP on the generation of in vivo primary and in vitro secondary cellular and humoral immune responses. At nontoxic doses of the compound, i.e. 20 and 40 mg/kg OSS-TMP, the in vivo generation of a primary cytotoxic T lymphocyte (CTL) response to alloantigen was significantly elevated, but this response was unaffected following restimulation of the splenocytes by alloantigen in vitro. The generation of an in vivo primary and in vitro secondary humoral responses to sheep red blood cells (SRBC) was elevated following a single dose of 40 mg/kg OSS-TMP. Administration of toxic doses of OSS-TMP, i.e. 60 and 80 mg/kg, did not alter the ability of splenocytes to generate a primary or secondary CTL response, but suppressed the generation of humoral immune responses. These results differ significantly from those observed in a similar system following acute administration of a structural analog, O,O,S-trimethyl phosphorothioate which was previously shown to have potent immunosuppressive activity at nontoxic doses.

Cytotoxic lymphokines produced by cloned human cytotoxic T lymphocytes. II. A novel CTL-produced cytotoxin that is antigenically distinct from tumor necrosis factor and alpha-lymphotoxin

We have cloned lines of IL 2-dependent human T cells derived from alloantigen, soluble antigen (tetanus toxoid), mitogen, or IL 2-stimulated peripheral blood lymphocytes and characterized their surface marker expression and cytolytic activity. The surface phenotype and cytolytic function was compared with the ability of these T cell clones to release cytotoxic lymphokines in response to mitogenic lectins. The cytotoxins released by these CTL clones were detected on the murine L929 target cells in a 16-hr assay. All of the T cell clones, whether stimulated by HLA alloantigens, tetanus toxoid, or mitogens, exhibited killer cell activity and the capacity to secrete a soluble cytotoxin(s). Specific polyclonal antisera to recombinant human tumor necrosis factor (rTNF) and human alpha-lymphotoxin (alpha LT) were unable to neutralize the cytotoxic activity released by most of these CTL clones. These results indicate that human CTL produce a novel antigenic form(s) of cytotoxin that we have termed CTL-toxin. Supernatants from several CTL clones yielded a cytotoxic activity that was partially neutralized (10 to 40%) by saturating levels of anti-TNF (but not anti-alpha LT) indicating that human CTL may be capable of producing a TNF-like molecule. Only two out of 60 CTL clones studied thus far produced a cytotoxic activity that was partially neutralized by anti-alpha LT (20 to 40%). Collectively, these results suggest that although both the CD4 and the CD8 subpopulations of human cytotoxic T cells may be capable of releasing several types of cytotoxins in response to mitogenic signals, the predominant cytotoxin is distinct from alpha LT and TNF.

Cytotoxic lymphokines produced by cloned human cytotoxic T lymphocytes. II. A novel CTL-produced cytotoxin that is antigenically distinct from tumor necrosis factor and alpha-lymphotoxin

We have cloned lines of IL 2-dependent human T cells derived from alloantigen, soluble antigen (tetanus toxoid), mitogen, or IL 2-stimulated peripheral blood lymphocytes and characterized their surface marker expression and cytolytic activity. The surface phenotype and cytolytic function was compared with the ability of these T cell clones to release cytotoxic lymphokines in response to mitogenic lectins. The cytotoxins released by these CTL clones were detected on the murine L929 target cells in a 16-hr assay. All of the T cell clones, whether stimulated by HLA alloantigens, tetanus toxoid, or mitogens, exhibited killer cell activity and the capacity to secrete a soluble cytotoxin(s). Specific polyclonal antisera to recombinant human tumor necrosis factor (rTNF) and human alpha-lymphotoxin (alpha LT) were unable to neutralize the cytotoxic activity released by most of these CTL clones. These results indicate that human CTL produce a novel antigenic form(s) of cytotoxin that we have termed CTL-toxin. Supernatants from several CTL clones yielded a cytotoxic activity that was partially neutralized (10 to 40%) by saturating levels of anti-TNF (but not anti-alpha LT) indicating that human CTL may be capable of producing a TNF-like molecule. Only two out of 60 CTL clones studied thus far produced a cytotoxic activity that was partially neutralized by anti-alpha LT (20 to 40%). Collectively, these results suggest that although both the CD4 and the CD8 subpopulations of human cytotoxic T cells may be capable of releasing several types of cytotoxins in response to mitogenic signals, the predominant cytotoxin is distinct from alpha LT and TNF.

A rat monoclonal antibody which interacts with mammalian ornithine decarboxylase at an epitope involved in phosphorylation

Ornithine decarboxylase was purified from androgen-treated mouse kidney to homogeneity and high specific activity. The purified enzyme was utilized for production and screening of rat monoclonal and polyclonal antibodies. A rat monoclonal antibody was isolated which was capable of immunoprecipitation of native mouse kidney ornithine decarboxylase activity or the [3H]difluoromethylornithine-inactivated enzyme. Phosphorylation of mouse ornithine decarboxylase by casein kinase-II prior to immunoprecipitation led to complete loss of the epitope recognized by the monoclonal antibody but did not alter recognition by polyclonal antibody. Mammalian ornithine decarboxylase activity obtained from several species, in crude or partially purified extracts, was subjected to quantitative immunoprecipitation with monoclonal and polyclonal antibody. Polyclonal antibody immunoprecipitated all of the ornithine decarboxylase activity from every extract tested, while monoclonal antibody was capable of only limited immunoprecipitation (60-80%). Due to the inability of the monoclonal antibody to recognize ornithine decarboxylase phosphorylated in vitro by casein kinase-II and the partial immunoprecipitation of ornithine decarboxylase activity from cell extracts, a portion of the ornithine decarboxylase molecule population must exist in a phosphorylated state. This immunological evidence further confirms existing data that the enzyme exists in at least two distinct forms.

The human LT system. XI. Identification of LT and "TNF-like" forms from stimulated natural killers, specific and nonspecific cytotoxic human T cells in vitro

These studies demonstrate that specific and nonspecific cytolytic human T cells can release LT forms in vitro. Nonspecific cytolytic T cells were derived from IL 2-dependent cultures initiated by allogeneic mixed lymphocyte reaction (AMLR). Specific cytolytic T cells (CTL) were derived from IL 2-dependent T cell clones, initiated by mixed lymphocyte reaction and specific for class II antigens. alpha-LT was the major lytic component released by these cells in IL 2-dependent cultures. However, on Con A stimulation or contact with target cells, both AMLR and CTL effectors release a new LT form. The new LT form released by AMLR and CTL effectors appear similar, for they both elute from gel filtration at 60,000 to 70,000 m.w. and migrate as a single peak with an Rf of 0.4 on 7% native PAGE tube gels. Moreover, testing these materials on a panel of target cells in vitro indicates that they are both nonspecific, and lyses NK-resistant target cells in vitro. Additional studies revealed that in vitro lytic activity of this form(s) is not affected by either anti-alpha-LT serum or a monoclonal reagent which inactivates macrophage cell toxins (MCT) and tumor necrosis factor (TNF). However, when these two immunologic reagents are tested together, activity is totally neutralized. Thus, this LT form expresses antigens in common with alpha-LT, MCT, and TNF. Finally, studies with NK-CF and NK-LT forms revealed that they were also completely neutralized with a mixture of anti-LT and monoclonal anti-TNF antibody. These data suggest that certain macrophage- and lymphocyte-derived cell toxins are interrelated.

The human LT system. XI. Identification of LT and "TNF-like" forms from stimulated natural killers, specific and nonspecific cytotoxic human T cells in vitro

These studies demonstrate that specific and nonspecific cytolytic human T cells can release LT forms in vitro. Nonspecific cytolytic T cells were derived from IL 2-dependent cultures initiated by allogeneic mixed lymphocyte reaction (AMLR). Specific cytolytic T cells (CTL) were derived from IL 2-dependent T cell clones, initiated by mixed lymphocyte reaction and specific for class II antigens. alpha-LT was the major lytic component released by these cells in IL 2-dependent cultures. However, on Con A stimulation or contact with target cells, both AMLR and CTL effectors release a new LT form. The new LT form released by AMLR and CTL effectors appear similar, for they both elute from gel filtration at 60,000 to 70,000 m.w. and migrate as a single peak with an Rf of 0.4 on 7% native PAGE tube gels. Moreover, testing these materials on a panel of target cells in vitro indicates that they are both nonspecific, and lyses NK-resistant target cells in vitro. Additional studies revealed that in vitro lytic activity of this form(s) is not affected by either anti-alpha-LT serum or a monoclonal reagent which inactivates macrophage cell toxins (MCT) and tumor necrosis factor (TNF). However, when these two immunologic reagents are tested together, activity is totally neutralized. Thus, this LT form expresses antigens in common with alpha-LT, MCT, and TNF. Finally, studies with NK-CF and NK-LT forms revealed that they were also completely neutralized with a mixture of anti-LT and monoclonal anti-TNF antibody. These data suggest that certain macrophage- and lymphocyte-derived cell toxins are interrelated.

Production, characterization, and applications of monoclonal antibodies reactive with soybean nodule xanthine dehydrogenase

Seven monoclonal antibodies were produced against soybean nodule xanthine dehydrogenase, an enzyme involved in ureide synthesis. Specificity of the seven monoclonal antibodies for xanthine dehydrogenase was demonstrated by immunopurifying the enzyme to homogeneity from a crude nodule extract using antibodies immobilized to Sepharose 4B beads. Each monoclonal antibody was covalently bound to Sepharose 4B beads for the preparation of immunoaffinity columns for each antibody. All seven antibodies were found to be of the IgG1,K subclass. A competitive, indirect enzyme-linked immunosorbent assay demonstrated that two of the seven antibodies shared a common epitope while the remaining five antibodies defined unique determinants on the protein. Rapid, large scale purification of active xanthine dehydrogenase to homogeneity was performed by immunoaffinity chromatography. The presence of xanthine dehydrogenase activity and protein in every organ of the soybean plant was determined. Crude extracts of nodules, roots, stems, and leaves cross-reacted with all seven monoclonal antibodies in an indirect enzyme-linked immunosorbent assay. A positive correlation was observed between the degree of cross-reactivity of a given organ and the level of enzyme activity in that organ. These data demonstrate that xanthine dehydrogenase is not nodule specific. Antigenic variability of xanthine dehydrogenase present in crude extracts from nodules of soybean, wild soybean, cowpea, lima bean, pea, and lupin were detected in the indirect enzyme-linked immunosorbent assay which corresponded to six binding patterns for xanthine dehydrogenase from these plant species. These results correspond well with the epitope determination data which showed that the seven antibodies bind to six different binding determinants on the enzyme.

Human, rat or mouse hybridomas secrete high levels of monoclonal antibodies following transplantation into mice with severe combined immunodeficiency disease (SCID)

Mice with severe combined immunodeficiency disease (SCID) have been investigated for their ability to grow xenogenic hybridomas of mouse, rat and human origin. Two rat X mouse hybridoma lines (187.1.10 and 3B9) and 1 mouse X mouse hybridoma (2D9) grown in pristane-treated SCID mice as ascites tumors showed a 100-200-fold increase in monoclonal antibody levels over the amount produced in vitro with a total yield up to 0.5 g of antibody per animal. A human X human hybridoma, CLL-11-D1, exhibited a 1000-fold increase in human immunoglobulin levels in ascites (1.3 mg/ml) as compared to that obtained in tissue culture. Analyses of the antibody protein in the SCID ascites produced by these hybridomas using protein electrophoresis, SDS polyacrylamide gel electrophoresis and high resolution isoelectric focusing indicated the antibodies were monoclonal and free from any contaminating immunoglobulins. Yields of monoclonal antibodies of over 90% purity could be obtained from the ascites by a single ammonium sulfate precipitation step. This study indicates that SCID mice provide several significant advantages over other in vivo methods for the production of pure monoclonal antibodies of human, rat, or mouse origin.

Cytotoxic lymphokines produced by cloned human cytotoxic T lymphocytes. I. Cytotoxins produced by antigen-specific and natural killer-like CTL are dissimilar to classical lymphotoxins

Several cloned lines of IL 2-dependent human T cells derived from alloantigen, mitogen, or IL 2-stimulated peripheral blood lymphocytes were examined for their surface marker expression, cytolytic activity in a 51Cr-release assay, and capacity to release cytotoxic lymphokines. Thirty cell lines exhibiting either antigen-specific natural killer cell activity or lectin-dependent killer cell function, which expressed either the CD4 or CD8 surface differentiation markers, were capable of producing cytotoxin(s) in response to the lectins phytohemagglutinin and concanavalin A. Cytotoxin activity was detected on the murine L929 target cell in a 16-hr cytotoxicity assay. In contrast, several nonlytic T cell tumor lines failed to produce a soluble cytotoxin. Antibodies capable of neutralizing human alpha-lymphotoxin were completely ineffective in inhibiting the cytotoxin(s) produced by any of the cytotoxic T lymphocytes (CTL) cell lines. Comparative gel filtration and HPLC hydrophobic chromatography of alpha-lymphotoxin and CTL toxin produced by the CTL-830.B2 clone revealed significant differences in their elution profiles. The CTL-produced toxin and alpha-lymphotoxin exhibited similar kinetics of lysis of the L929 target cells, with 50% target cell lysis occurring at 10 hr. These data indicate human CTL produce a cytotoxin(s) antigenically distinct from alpha-lymphotoxin and imply that human cytolytic effector T cells are not the cellular source for the production of human alpha-lymphotoxin. The relationship of alpha-lymphotoxin and CTL toxin production was investigated in unseparated peripheral blood mononuclear cells stimulated with lectins or IL 2 for 1 and 5 days. Anti-alpha-lymphotoxin antibodies were capable of neutralizing only 30 to 50% of the cytotoxic activity in 24-hr supernatants. Cytotoxic activity in supernatants harvested after 120 hr stimulation with PHA or Con A was neutralized 70 to 100%, whereas the toxin(s) released from IL 2-stimulated lymphocytes was only neutralized 30%. These data suggest the observed heterogeneity of cytotoxic lymphokines produced by unseparated mononuclear cells depends in part on the subpopulations of effector cells responding to a given stimulus and the capacity of different subpopulations to produce distinct cytotoxins.

Cytotoxic lymphokines produced by cloned human cytotoxic T lymphocytes. I. Cytotoxins produced by antigen-specific and natural killer-like CTL are dissimilar to classical lymphotoxins

Several cloned lines of IL 2-dependent human T cells derived from alloantigen, mitogen, or IL 2-stimulated peripheral blood lymphocytes were examined for their surface marker expression, cytolytic activity in a 51Cr-release assay, and capacity to release cytotoxic lymphokines. Thirty cell lines exhibiting either antigen-specific natural killer cell activity or lectin-dependent killer cell function, which expressed either the CD4 or CD8 surface differentiation markers, were capable of producing cytotoxin(s) in response to the lectins phytohemagglutinin and concanavalin A. Cytotoxin activity was detected on the murine L929 target cell in a 16-hr cytotoxicity assay. In contrast, several nonlytic T cell tumor lines failed to produce a soluble cytotoxin. Antibodies capable of neutralizing human alpha-lymphotoxin were completely ineffective in inhibiting the cytotoxin(s) produced by any of the cytotoxic T lymphocytes (CTL) cell lines. Comparative gel filtration and HPLC hydrophobic chromatography of alpha-lymphotoxin and CTL toxin produced by the CTL-830.B2 clone revealed significant differences in their elution profiles. The CTL-produced toxin and alpha-lymphotoxin exhibited similar kinetics of lysis of the L929 target cells, with 50% target cell lysis occurring at 10 hr. These data indicate human CTL produce a cytotoxin(s) antigenically distinct from alpha-lymphotoxin and imply that human cytolytic effector T cells are not the cellular source for the production of human alpha-lymphotoxin. The relationship of alpha-lymphotoxin and CTL toxin production was investigated in unseparated peripheral blood mononuclear cells stimulated with lectins or IL 2 for 1 and 5 days. Anti-alpha-lymphotoxin antibodies were capable of neutralizing only 30 to 50% of the cytotoxic activity in 24-hr supernatants. Cytotoxic activity in supernatants harvested after 120 hr stimulation with PHA or Con A was neutralized 70 to 100%, whereas the toxin(s) released from IL 2-stimulated lymphocytes was only neutralized 30%. These data suggest the observed heterogeneity of cytotoxic lymphokines produced by unseparated mononuclear cells depends in part on the subpopulations of effector cells responding to a given stimulus and the capacity of different subpopulations to produce distinct cytotoxins.

A rat anti-mouse kappa chain specific monoclonal antibody, 187.1.10: purification, immunochemical properties and its utility as a general second-antibody reagent

A rat IgG1 monoclonal antibody, produced by hybridoma 187.1.10, exhibits specificity for mouse immunoglobulins containing kappa light chains (Yelton et al., 1981). The 187.1.10 hybridoma cell line secreted upwards of 200 micrograms/ml of monoclonal antibody in tissue culture and the secreted product was purified in a single step by antigen-immunoadsorbent affinity chromatography. The homogeneity of the purified 187.1.10 protein was determined by isoelectrofocusing and SDS gel electrophoresis. Equilibrium binding analyses of the radioiodinated 187.1.10 antibody indicated a strong interaction with its antigen of KA = 2 X 10(9) l/mole. The 187.1.10 antibody did not readily bind to Staph. aureus protein A unless it was complexed with antigen. The binding of immune complexes of 187.1.10 to protein A was shown to be dependent on the Fc region of the antigen. The utility of the 187.1.10 monoclonal antibody as a general second antibody reagent for studying mouse immunoglobulins was demonstrated in a rapid solid phase immunoprecipitation assay to detect and analyze radioiodinated membrane proteins of a human cytotoxic T cell line.

Rapid colorimetric assay for cell viability: application to the quantitation of cytotoxic and growth inhibitory lymphokines

A rapid colorimetric microtiter assay has been developed to detect cytotoxic lymphokines produced by human lymphocytes activated with lectins or tumor cells. The viability of lymphotoxin-treated target cells was detected using a tetrazolium dye that is reduced to a blue formazan by living but not dead cells. The amount of dye formed was quantitated using a microplate spectrophotometer (ELISA plate reader) and visual observations confirmed the amount of formazan dye produced was directly proportional to the number of viable target cells. The advantages of using this colorimetric method are that it requires no washing steps or radioisotopes and its precision and rapidity. Optimal conditions were established using the murine L929 and human ESH -5L cell lines as target cells for detecting lymphotoxins produced by human lymphocytes. The data indicate that the L929 cell line was 10-50-fold more sensitive than the ESH -5L line to the lytic activity of cytotoxins produced by human phytohemagglutinin-P-activated T lymphocytes, or the cytotoxins produced by peripheral blood lymphocytes stimulated with various tumor cell lines. This assay system was also useful in detecting antibodies capable of neutralizing lymphotoxin activity and thus should be a suitable method to aid in the molecular characterization of these lymphokines.

Recognition of HLA-A2 mutant and variant target cells by an HLA-A2 allospecific human cytotoxic T lymphocyte line

HLA-A2 specific human cytotoxic T lymphocytes (CTL) cell lines have been developed using T cell growth factor and coculture of peripheral blood lymphocytes with selected allogeneic target cell lines. The CTL-8 line showed specificity for human leukocyte antigens (HLA)-A2 bearing target cells after 5 weeks in culture when tested against a panel of 14 lymphoblastoid cell lines in a 51Chromium (51Cr) release assay. Purified anti-human leukocyte antigens (HLA) monoclonal antibodies W6/32 and PA2.1 inhibited cytolysis by 85% and 60%, respectively. The CTL-8 line lysed non-HLA-A2 target cells in the presence of lectins concanavalin A (Con A) or phytohemagglutinin-P lectin (PHA-P) indicating the specificity of cytolysis was not due to nonspecific resistance of target cells to the CTL-lytic mechanism. The T5-1 HLA-A2 mutant cell series were tested as targets for the CTL-8 line. Cell clones 8.18.1, 8.21.1 and 8.6.1, which express altered HLA-A2 molecules as determined by their decreased reactivity with allospecific monoclonal antibodies, were lysed by the CTL-8 line as efficiently as the T5-1 wild type. These cell lines also acted as efficient cold target competitors for a normal HLA-A2 target cell. The 8.14.1 cell clone expressed a lower amount of HLA-A2 alloantigen and showed a corresponding decreased reactivity with CTL-8 in direct cytolytic and cold target competitive inhibition assays. In contrast, the M7 and DK1 HLA-A2 variant cell lines, which express normal HLA-A2 serological determinants, were inefficiently lysed by CTL-8 and did not act as competitive inhibitors of normal HLA-A2 target cells. These results support the concept that the alloantigenic determinant(s) recognized by T cells and antibodies occur at separate regions on the HLA-A2 molecule.

Human lymphocyte function associated antigen-1 (LFA-1): identification of multiple antigenic epitopes and their relationship to CTL-mediated cytotoxicity

Human lymphocyte function-associated antigen (LFA)-1, a heterodimeric lymphocyte surface glycoprotein of 177,000 and 95,000 relative molecular weight has been implicated to function in the cytotoxic T lymphocyte (CTL) effector mechanism. Seven mouse hybridoma lines producing monoclonal antibodies (MAb) reactive with this structure were studied. Three unique and 3 partially over-lapping epitopes on human LFA-1 were defined by competitive cross inhibition binding assays using biosynthetically labeled anti-LFA-1 MAb. In contrast, of five rat antimouse LFA-1 MAb, all five recognized a common or shared epitope. An HLA-B7 specific human CTL line expressed 1.1 X 10(5) LFA-1 sites per cell with a direct saturation binding assay. Human CTL expressed two to four times more LFA-1 than peripheral blood lymphocytes or B and T lymphoblastoid cell lines. Titration of each of the anti-LFA-1 MAb in a 51chromium release cytolytic assay revealed quantitative differences in the ability of the different anti-LFA-1 MAb to block cytolysis indicating distinct functional and antigenic epitopes exist on the human LFA-1 molecule. Anti-LFA-1 MAb reversibly inhibited the CTL reaction by slowing the initial rate of cytolysis. These results suggest anti-LFA-1 MAb inhibit CTL function by specific blockade of a functionally relevant molecule.

Human lymphocyte function associated antigen-1 (LFA-1): identification of multiple antigenic epitopes and their relationship to CTL-mediated cytotoxicity

Human lymphocyte function-associated antigen (LFA)-1, a heterodimeric lymphocyte surface glycoprotein of 177,000 and 95,000 relative molecular weight has been implicated to function in the cytotoxic T lymphocyte (CTL) effector mechanism. Seven mouse hybridoma lines producing monoclonal antibodies (MAb) reactive with this structure were studied. Three unique and 3 partially over-lapping epitopes on human LFA-1 were defined by competitive cross inhibition binding assays using biosynthetically labeled anti-LFA-1 MAb. In contrast, of five rat antimouse LFA-1 MAb, all five recognized a common or shared epitope. An HLA-B7 specific human CTL line expressed 1.1 X 10(5) LFA-1 sites per cell with a direct saturation binding assay. Human CTL expressed two to four times more LFA-1 than peripheral blood lymphocytes or B and T lymphoblastoid cell lines. Titration of each of the anti-LFA-1 MAb in a 51chromium release cytolytic assay revealed quantitative differences in the ability of the different anti-LFA-1 MAb to block cytolysis indicating distinct functional and antigenic epitopes exist on the human LFA-1 molecule. Anti-LFA-1 MAb reversibly inhibited the CTL reaction by slowing the initial rate of cytolysis. These results suggest anti-LFA-1 MAb inhibit CTL function by specific blockade of a functionally relevant molecule.

Recognition of HLA-A2 mutant and variant target cells by an HLA-A2 allospecific human cytotoxic T lymphocyte line

HLA-A2 specific human cytotoxic T lymphocytes (CTL) cell lines have been developed using T cell growth factor and coculture of peripheral blood lymphocytes with selected allogeneic target cell lines. The CTL-8 line showed specificity for human leukocyte antigens (HLA)-A2 bearing target cells after 5 weeks in culture when tested against a panel of 14 lymphoblastoid cell lines in a 51Chromium (51Cr) release assay. Purified anti-human leukocyte antigens (HLA) monoclonal antibodies W6/32 and PA2.1 inhibited cytolysis by 85% and 60%, respectively. The CTL-8 line lysed non-HLA-A2 target cells in the presence of lectins concanavalin A (Con A) or phytohemagglutinin-P lectin (PHA-P) indicating the specificity of cytolysis was not due to nonspecific resistance of target cells to the CTL-lytic mechanism. The T5-1 HLA-A2 mutant cell series were tested as targets for the CTL-8 line. Cell clones 8.18.1, 8.21.1 and 8.6.1, which express altered HLA-A2 molecules as determined by their decreased reactivity with allospecific monoclonal antibodies, were lysed by the CTL-8 line as efficiently as the T5-1 wild type. These cell lines also acted as efficient cold target competitors for a normal HLA-A2 target cell. The 8.14.1 cell clone expressed a lower amount of HLA-A2 alloantigen and showed a corresponding decreased reactivity with CTL-8 in direct cytolytic and cold target competitive inhibition assays. In contrast, the M7 and DK1 HLA-A2 variant cell lines, which express normal HLA-A2 serological determinants, were inefficiently lysed by CTL-8 and did not act as competitive inhibitors of normal HLA-A2 target cells. These results support the concept that the alloantigenic determinant(s) recognized by T cells and antibodies occur at separate regions on the HLA-A2 molecule.