A specific serine proteinase is inducible in Lyt-2+,L3T4- and Lyt-2-,L3T4+ T cells in vitro but is mainly associated with Lyt-2+,L3T4- effector cells in vivo

Granzyme activity in the inflamed lung is not controlled by endogenous serine proteinase inhibitors

Numerous lung diseases, such as hypersensitivity pneumonitis (HP), are characterized by the presence of activated alveolar CTL and NK cells. Since these cells produce granzymes, granzyme A and B levels in bronchoalveolar lavage (BAL) fluids from 14 normal subjects and 12 patients with HP were measured by ELISA. Median (range) BAL granzyme A and B levels were 4 (0-37) and 0 (0-6) pg/ml in normal subjects. BAL granzyme levels were significantly higher in HP patients, being at 74 (0-1,889) and 10 (0-78) pg/ml for granzymes A and B, respectively. In vitro, neither of the three main serine protease inhibitors of the lung, namely alpha1-antitrypsin, secretory leukocyte protease inhibitor, and elafin, showed any effect on granzyme A or B activity. In addition, granzyme A was shown to be fully active in BAL fluids. Hence, these data show that granzyme activity may be poorly controlled by protease inhibitors in inflamed tissues. Thus, granzymes could contribute to tissue remodeling and inflammation characterizing HP.

Elafin, a serine elastase inhibitor, attenuates post-cardiac transplant coronary arteriopathy and reduces myocardial necrosis in rabbits afer heterotopic cardiac transplantation

We have related experimentally induced post-cardiac transplant coronary arteriopathy to increased elastolytic activity, IL-1beta, fibronectin-mediated inflammatory and smooth muscle cell (SMC) migration, and SMC proliferation. Since our in vitro studies show that a serine elastase releases SMC mitogens and facilitates IL-lbeta induction of fibronectin, we hypothesized that administration in vivo of the specific serine elastase inhibitor, elafin, would decrease the post-cardiac transplant coronary arteriopathy. Cholesterol-fed rabbits underwent a heterotopic cardiac transplant without immunosuppression and received elafin (1.79 mg/kg per d continuous infusion after a 9 mg bolus, n = 6) or vehicle (n = 6). 1 wk later, hearts were harvested for morphometric, immunohistochemical, and biochemical analyses. A > 70% decrease in the total number of coronary arteries with intimal thickening in elafin-treated compared to control donor hearts (P < 0.002) was associated with reduced vascular elastolytic activity judged by fewer breaks in the internal elastic lamina (P < 0.03), less accumulation of immunoreactive fibronectin (P < 0.02), and reduced cell proliferation quantified by proliferating cell nuclear antigen (P < 0.0001). Despite myocardial lymphocytic infiltration, wet weight of elafin-treated donor hearts was reduced by 50% compared to untreated controls (P < 0.002) and associated with relative preservation of myocyte integrity, instead of extensive myocardial necrosis (P < 0.004). This protective effect correlated with decreased myocardial elastolytic activity (P < 0.0001) and inflammatory cell proliferation (P < 0.0001) and with an elafin-inhibitable elastase in lymphocytes. Serine elastase activity thus appears an important therapeutic target for post-cardiac transplant coronary arteriopathy and myocardial necrosis induced by rejection.

Degradative activity of granzyme A on skeletal muscle proteins in vitro: a possible molecular mechanism for muscle fiber damage in polymyositis

The importance of cytotoxic T lymphocytes (CTLs) in the autoimmune inflammatory myopathies, especially polymyositis (PM), has been emphasized. We have studied the degradative activity of granzyme A, a cytotoxic molecule with trypsin-like specificity in CTL granules, on several muscle proteins in vitro. Our study reveals that granzyme A hydrolyzes dystrophin, myosin, and nebulin, but not laminin, alpha-actinin, vinculin, and connectin in vitro. Among these proteins, nebulin is more susceptible to proteolysis, followed by dystrophin, myosin heavy chain, and myosin light chains, in that order. This result implies an important role of granzyme A in CTL-mediated muscle fiber damage in PM.

Islet cells but not thyrocytes are susceptible to lysis by NK cells

BB rats develop both pancreatic insulitis and lymphocytic thyroiditis, but whereas spontaneous autoimmune diabetes is common, hypothyroidism is rare. Splenic natural killer (NK) cells from acutely diabetic (AD) BB rats and from athymic nude rats are known to be cytotoxic to rat islet cells in vitro. To investigate possible differential tissue susceptibility to lysis by NK cells or their cytokines such as cytolysin (perforin) or NK cytotoxic factor (NKCF), we used an in vitro 51Cr-release assay to measure the cytotoxicity of splenocytes, cytolysin or NKCF against Wistar Furth (WF) and Fischer 344 (F-344) rat islet cells, and FRTL-5 F-344-derived and WRT Wistar-derived rat thyrocytes. The results demonstrated that spleen cells from AD-BB (RT1u) rats and athymic F-344 nude (RT11) rats are cytotoxic to WF (RT1u) islets and F-344 (RT11) islets, but not to FRTL-5 (RT11) or WRT (class I RT11) thyrocytes. WF and F-344 rat spleen cells were not cytotoxic to any of these cells. Thyrocytes are known to express class II molecules on their surface in chronic thyroiditis. We found that treatment of thyrocytes with interferon-gamma (IFN-gamma) induced class II expression but did not increase the cytotoxicity of splenocytes against these cells. Cytolysin and NKCF were both cytotoxic to islets in a dose dependent manner, but FRTL-5 thyrocytes were resistant to killing by these cytokines. These findings suggest that islet cells and thyrocytes in vitro are differentially susceptible to lysis by NK cells.

Mechanism of killing by virus-induced cytotoxic T lymphocytes elicited in vivo

The mechanism of lysis by in vivo-induced cytotoxic T lymphocytes (CTL) was examined with virus-specific CTL from mice infected with lymphocytic choriomeningitis virus (LCMV). LCMV-induced T cells were shown to have greater than 10 times the serine esterase activity of T cells from normal mice, and high levels of serine esterase were located in the LCMV-induced CD8+ cell population. Serine esterase was also induced in purified T-cell preparations isolated from mice infected with other viruses (mouse hepatitis, Pichinde, and vaccinia). In contrast, the interferon inducer poly(I.C) only marginally enhanced serine esterase in T cells. Serine esterase activity was released from the LCMV-induced T cells upon incubation with syngeneic but not allogeneic LCMV-infected target cells. Both cytotoxicity and the release of serine esterase were calcium dependent. Serine esterase released from disrupted LCMV-induced T cells was in the form of the fast-sedimenting particles, suggesting its inclusion in granules. Competitive substrates for serine esterase blocked killing by LCMV-specific CTL, but serine esterase-containing granules isolated from LCMV-induced CTL, in contrast to granules isolated from a rat natural killer cell tumor line, did not display detectable hemolytic activity. Fragmentation of target cell DNA was observed during the lytic process mediated by LCMV-specific CTL, and the release of the DNA label [125I]iododeoxyuridine from target cells and the accompanying fragmentation of DNA also were calcium dependent. These data support the hypothesis that the mechanism of killing by in vivo-induced T cells involves a calcium-dependent secretion of serine esterase-containing granules and a target cell death by a process involving nuclear degradation and DNA fragmentation.

Protease nexin-1 complexes and inhibits T cell serine proteinase-1

The T cell serine proteinase-1 (TSP-1) which most probably is involved in cell killing by cytotoxic T cells is inhibited by protease nexin-1 (PN-1), an extravascular serine protease inhibitor. The inhibition is irreversible and correlates with formation of SDS-stable complexes between the two proteins. Two distinct species of complexes (91 and 122 kDa) are observed upon SDS-PAGE analysis of the reacted proteins, indicating that PN-1 is capable of complexing and inhibiting both subunits of the homodimeric TSP-1 molecule. Heparin (2 micrograms/ml) increases the association rate constant from 4.2 x 10(4) M-1 sec-1 to 4.8 x 10(5) M-1 sec-1. These observations suggest that PN-1 may function as a major extravascular inhibitor of TSP-1 released from cytotoxic T lymphocytes.

N-alpha-benzyloxycarbonyl-L-lysine thiobenzyl ester (BLT) serine esterase in human cytolytic effector cells and cell line targets

The granules of in vitro primed cytotoxic mouse T cells and cytotoxic cell lines have been shown to contain high levels of N-alpha-benzyloxycarbonyl-L-lysine thiobenzyl ester (BLT) esterase. The enzyme activity has been suggested to be associated with the cytotoxic capacity of killer cells. We investigated human leucocytes and found that neutrophils, monocytes, cytotoxic T lymphocytes (CTL), natural killer (NK) cells [large granular lymphocytes (LGL)], and interleukin 2 activated killer (LAK) cells, which all display efficient cytotoxic capacity, show only marginal BLT esterase activity. The low BLT esterase activity in human lymphocytes increases about twofold when cells are stimulated in vitro with interleukin 2 (IL-2), phytohaemagglutinin (PHA), or cultured in mixed lymphocyte culture (MLC). Mouse T lymphocytes have about 20 times more BLT esterase activity than human T lymphocytes. The BLT activity in mouse T cells also increases about twofold in MLC. The human leukaemia cell lines (K562, U937, MOLT-4, Jurkat) and the mouse mastocytoma line (P815), which are frequently used as target cells, contain more BLT esterase activity than human resting or activated lymphocytes. We did not find a direct correlation between the cytotoxic capacity and the BLT esterase activity of killer cells.

Granzyme A expression by normal rat natural killer (NK) cells in vivo and by interleukin 2-activated NK cells in vitro

Granzyme A (TSP-1) is a serine esterase expressed in cytotoxic T and natural killer (NK) cell lines. Its presence in in vivo primed T cells is disputed at present. Here we show that normal rat NK cells contain granzyme A in vivo and that its expression is augmented by their short-term in vitro treatment with IL 2. Granzyme A expression in a NK cell population with LAK activity has also been examined.

CTL: virus control cells first and cytolytic cells second? DNA fragmentation, apoptosis and the prelytic halt hypothesis

It is usually presumed that cytotoxic T lymphocytes (CTL) stop viral replication by lysing infected cells before a full virus yield has been assembled. Unlike complement-mediated lysis, however, CTL induce apoptosis, including fragmentation of target cell DNA. Why should CTL do this? Here, Eric Martz and Donna Howell suggest that since the major function of CTL appears to be control of viruses, CTL may be able to halt viral replication without inducing rapid lysis. It may be more useful to think of CTL as virus control cells rather than as cytolytic cells.

Trypsin does not reconstitute responsiveness to lipopolysaccharide in the strain C3H/HeJ, but is a B-cell mitogen-like lipopolysaccharide, stimulating a different subpopulation

The effect of trypsin on mouse spleen cells and enriched B cells, added alone or together with lipopolysaccharide (LPS), was investigated. With trypsin, proliferation in serum free spleen cell cultures was 2-6 times greater than the background using cells from LPS responder strains, and 2-4 times the background with cells from the C3H/HeJ strain. Trypsin also induced the formation of a low number of IgM plaque forming cells (PFC). When added together with LPS, trypsin increased the proliferation caused by LPS alone by 10-50% with cells from LPS responder strains and by 50-100% with cells from the LPS non-responder strain C3H/HeJ. Trypsin enhanced proliferation in cultures maximally stimulated by LPS. The increased proliferation obtained when trypsin was added to LPS-stimulation of cells from the C3H/HeJ strain, was therefore not interpreted as a reconstitution of the LPS response. We conclude that trypsin has a moderate mitogenic effect on mouse B cells, stimulating the cells to proliferate and secrete IgM. The mechanism of action is unknown, but is different and independent from the action of LPS.

Expression of cytoplasmic granules with T cell-associated serine proteinase-1 activity in Ly-2+(CD8+) T lymphocytes responding to lymphocytic choriomeningitis virus in vivo

Monoclonal antibodies (mAb) with specificity for the T cell-associated serine proteinase-1 of the mouse (MTSP-1) were used to study expression and storage of this enzyme in T lymphocytes during lymphocytic choriomeningitis (LCM) virus infection in vivo. Immunohistochemical analysis of splenic tissue at the peak of LCM virus-specific T cell-mediated cytolytic responses, i.e., at day 7 post infection, revealed high numbers of MTSP-1+ T lymphocytes in the interfollicular T cell-dependent area of the spleen. More than 50% of Ly-2+(CD8+) cells but only low numbers of Ly-2-(CD8-) cells, previously enriched by flow cytofluorometry, contained large amounts of cytoplasmic granules which stained both with MTSP-1-specific mAb and the esterase substrate N-alpha-benzyloxycarbonyl-L-lysine thiobenzyl ester. These data demonstrate that in vivo generated LCM virus-induced cytolytic T lymphocytes develop cytoplasmic storage granules containing MTSP-1 and suggest that the mechanism of granule exocytosis is operative in vivo; possibly MTSP-1 is one effector molecule participating in the Ly-2+(CD8+) T lymphocyte-mediated control of virus infection.

Inhibition of lymphocyte protease granzyme A by antithrombin III

T-lymphocytes contain a cytoplasmic granule associated homo-dimeric protease designated granzyme A. Upon T-cell target cell interaction, the granules undergo exocytosis and granzyme A, and other granule constituents, are released. Here we show that granzyme A secreted into plasma is immediately inactivated by antithrombin III. The rate of complex formation is enhanced 400-fold in the presence of heparin. Two different complexes are generated: granzyme A-antithrombin III and granzyme A-(antithrombin III)2, respectively, indicating that both active centers of granzyme A are functional. Thus, the proteolytic activity of lymphocyte protease granzyme A, whose physiologically relevant function is unknown, is well regulated in plasma.

A T cell- and natural killer cell-specific, trypsin-like serine protease. Implications of a cytolytic cascade

A new trypsin-like serine protease was cloned from both a murine cytotoxic T lymphocyte and a human PHA-stimulated peripheral blood lymphocyte cDNA library. In both the mouse and human system, this transcript had a T cell- and NK-specific distribution, being detected in cytotoxic T lymphocytes (CTL), some T-helper clones, and NK, but not in a variety of normal tissues. T-cell activation with Con A plus IL-2 induced mouse spleen cells to express this gene with kinetics correlating with the acquisition of cytolytic capacity. Both the mouse and human nucleotide sequences of this gene encoded an amino acid sequence with 25-40% identity to members of the serine protease family. The active-site "charge-relay" residues (His-57, Asp-102, and Ser-195 of the chymotrypsin numbering system) are conserved, as well as the trypsin-specific Asp (position 189 in trypsin). We reviewed the evidence of this serine protease's role in lymphocyte lysis and proposed a "lytic cascade." We discussed the biological and clinical implications of a cascade, proposing these enzymes as markers for cytolytic cells and as targets for rational drug therapy. Genetic and acquired deficits in the lethal hit-delivery system are considered as a basis for approaching some immunodeficiency states, including severe EBV infections, T-gamma leukemias, and T8+ lymphocytosis syndromes.

Induction of T cell serine proteinase 1 (TSP-1)-specific mRNA in mouse T lymphocytes

An oligonucleotide probe corresponding to nucleotides of a cDNA encoding the T cell-associated proteinase 1 (TSP-1) was chosen to study the induction and expression of TSP-1-specific transcripts in mouse T lymphocytes and tissues. We demonstrate that TSP-1 mRNA is only expressed in activated T lymphocytes and is absent from all mouse tissues tested including those containing resting mature T lymphocytes. Expression of the TSP-1 gene was observed in T lymphocytes in vitro in response to either phorbolester (phorbol 12-myristate 13-acetate), Ca2+ ionophore (A23187), lectin or alloantigen. In general, TSP-1 mRNA appeared and peaked later compared to interleukin 2 transcripts. Furthermore, TSP-1 mRNA was inducible in vitro in both Ly-2+ and L3T4+ lymphocyte populations treated with alloantigen and/or lectin. The transcription of the TSP-1 gene was always accompanied by the expression of proteinase activity. High expression of TSP-1 transcripts was also observed in in vivo derived T effector cells specific for lymphocytic choriomeningitis virus. However, TSP-1 mRNA was predominantly associated with virus-specific Ly-2+ T cells and correlated with their proteinase and cytolytic activities. The data suggest that TSP-1 gene transcription is a useful marker to characterize T effector cells in vitro and in vivo.

Determination of frequency of T cells expressing the T cell-specific serine proteinase 1 (TSP-1) reveals two types of L3T4+ T lymphocytes

TSP-1 is a murine T cell-specific serine proteinase which is exclusively expressed in activated but not in resting T lymphocytes. Among T lymphocyte clones tested so far the enzyme was found to be associated with all Ly-2+ but only with a fraction of L3T4+ lines. Here we have applied a limiting dilution system to determine the frequency of precursor cells of resting L3T4+ and Ly-2+ lymphocytes which can be induced in vitro by antigen/lectin to express TSP-1. T cell subsets were either positively enriched by flow cytofluorometry cell sorting or by negative selection using monoclonal antibodies and complement. Following stimulation of lymphocytes in vitro, individual microwells were tested for growth by visual examination and for the TSP-1 protein/enzyme by analyzing cell lysates using either a specific rabbit anti-TSP-1 antiserum and/or the chromogenic model peptide substrate H-D-Pro-Phe-Arg-p-nitroanilide. Moreover, a large panel of L3T4+ and Ly-2+ T lymphocyte clones generated from primary cultures were similarly investigated. In some cell cultures the presence of TSP-1 was also tested on the mRNA level using a TSP-1-specific oligonucleotide probe. The data show that the majority, if not all, of antigen/lectin-induced-Ly-2+ T cells expressed TSP-1. In contrast, only 12%-27% of the growing lectin or antigen-reactive L3T4+ lymphocytes were positive for the enzyme. Studies performed in parallel with L3T4+ and Ly-2+ lymphocyte populations sensitized in bulk culture showed that under these conditions similar levels of TSP-1-specific mRNA and enzyme activity are detected in both subsets. The finding of primary L3T4+ T lymphocyte clones with distinct patterns of TSP-1 production provides evidence for the existence of two types of L3T4+ effector cells with different functional capacities. The data also suggest a cooperation between distinct L3T4+ lymphocytes for induction of optimal TSP-1 activity in L3T4+ T cells.

Granzymes, a family of serine proteases released from granules of cytolytic T lymphocytes upon T cell receptor stimulation

The cytolytic potential of T effector cells appears to be intimately related to the presence of proteins stored in specialized cytoplasmic granules. A striking biological property of isolated granules is their lytic activity for a variety of target cells in a nonrestricted manner. Proteins contained within these granules of CTLs are specifically released upon target cell recognition. We have isolated and characterized six granule-associated proteins in two murine CTL lines in addition to the pore-forming and target membrane-disrupting perforin. Six full length cDNA clones have been identified in a CTL-specific cDNA expression library which code for the granule-associated serine esterases, designated as granzymes A to F. Granzymes A and B represent the genuine proteins encoded by the H factor/CTLA-3 cDNA and the CTLA-1/CCPI cDNA, respectively. The covalent amino acid structures of all six granzymes show the hallmarks for serine proteases and are highly related to that of rat mast cell protease I and II and cathepsin G, which have been found in granules of mast cells and neutrophilic granulocytes, respectively. The primary translation products are processed by removal of a hydrophobic signal peptide and a two residue-long propeptide at the amino-terminus. Immuno-electron microscopy shows that granzymes and perforin are stored together within secretory granules of CTLs. Simultaneous release of at least two of these granzymes has been observed during degranulation of a murine CTL line by anti-T3 antibodies. The biological role, particularly the proteolytic events elicited by granzyme A and other granzymes in the context of target cell recognition, are not known at present. It is unlikely that they form a proteolytic activation cascade together with pore-forming proteins analogous to the complement system. The strictly regulated secretion of granzymes and the lack of measurable enzymatic activity in the case of granzymes B, C, E and F towards a variety of synthetic substrates suggest a highly specific function for each of them.

Perforin-dependent and -independent pathways of cytotoxicity mediated by lymphocytes

There is little doubt at the present time that both perforin-dependent and -independent pathways are important in mediating the cytotoxicity associated with lymphocytes. The cell distribution of perforin, initially thought to include both CTL and NK cells, now must be viewed with caution because all previous biochemical studies on CTL have been conducted with cell lines propagated in long-term cultures in the presence of T cell growth factors (IL-2 and perhaps some still undefined factors). Under these conditions, CTL are known to assume a broader, NK-like specificity in target cell killing and may thus differ significantly from primary CTL generated in the body. Accordingly, perforin does not seem to be present in primary CTL activated directly through mixed lymphocyte reactions. It remains to be shown how primary CTL lyse target cells in vivo. Initial studies conducted in several laboratories have already provided some clues. It now seems that even in cultured, perforin-containing CTL, the perforin pathway is not an obligatory mechanism required for target cell killing. Other pathways, possibly involving TNF/lymphotoxin-like molecules, may play a direct role in this type of cytotoxicity. Other still unidentified factors now also need to be sought, including membrane polypeptides that may develop cytotoxicity directly upon cell contact and binding. Although from the studies reviewed here it is clear now that perforin has a more limited role in cell killing than originally proposed, it is still intriguing that it should share structural and functional homologies with complement proteins, drawing paradoxical analogies between two systems (the cellular and the humoral immune systems) which have evolved to become specialized to carry out separate immunological tasks. The cloning of the genes for perforin and for all the C proteins that comprise the MAC should reveal important information on how these genes originated and then diverged during evolution. The cellular distribution of other granule products, such as serine esterases, also must be viewed with caution. A serine esterase activity was initially thought to be CTL-specific. This information stimulated an intensive research activity in many laboratories that resulted in both the purification of a serine esterase family and the cloning of several serine esterase transcripts. It is becoming clear from recent evidence that this group of enzymes is not truly CTL-specific and therefore would not be expected to develop any function rendered absolutely necessary for cytolysis.(ABSTRACT TRUNCATED AT 400 WORDS)

A comparison of the cytolytic properties of murine primary CD8+ cytotoxic T lymphocytes and cloned cytotoxic T cell lines

Lysates of many highly cytolytic murine primary CD8+ cytotoxic T lymphocytes (CTLs) have no detectable hemolytic activity and only traces of serine esterase activity, indicating a striking paucity or absence of the perforin-rich secretory granules that are abundant in the cytoplasm of murine cloned CTL cell lines. Nevertheless, the primary CTLs are almost as resistant to granule-mediated lysis as CTL cell lines. Moreover, target cells that are lysed by all CTLs so far tested, whether primary or cell lines, show similar rapid and marked increases in intracellular calcium and breakdown of DNA into nucleosome-sized fragments. A parsimonious explanation for all of these findings is that primary CTLs, like the CTL cell lines, exercise their cytolytic activity by means of perforin, but the amounts needed are extremely small and below the level of detection by the current relatively insensitive hemolytic assays.

Cloning and chromosomal assignment of a human cDNA encoding a T cell- and natural killer cell-specific trypsin-like serine protease

A cDNA clone encoding a human T cell- and natural killer cell-specific serine protease was obtained by screening a phage lambda gt10 cDNA library from phytohemagglutinin-stimulated human peripheral blood lymphocytes with the mouse Hanukah factor cDNA clone. In an RNA blot-hybridization analysis, this human Hanukah factor cDNA hybridized with a 1.3-kilobase band in allogeneic-stimulated cytotoxic T cells and the Jurkat cell line, but this transcript was not detectable in normal muscle, liver, tonsil, or thymus. By dot-blot hybridization, this cDNA hybridized with RNA from three cytolytic T-cell clones and three noncytolytic T-cell clones grown in vitro as well as with purified CD16+ natural killer cells and CD3+, CD16- T-cell large granular lymphocytes from peripheral blood lymphocytes (CD = cluster designation). The nucleotide sequence of this cDNA clone encodes a predicted serine protease of 262 amino acids. The predicted protein has a 22-amino acid presegment, a 6-amino acid prosegment, and an active enzyme of 234 amino acids with a calculated unglycosylated molecular weight of 25,820. The active enzyme is 71% and 77% similar to the mouse sequence at the amino acid and DNA level, respectively. The human and mouse sequences conserve the active site residues of serine proteases--the trypsin-specific Asp-189 and all 10 cysteine residues. The gene for the human Hanukah factor serine protease is located on human chromosome 5. We propose that this trypsin-like serine protease may function as a common component necessary for lysis of target cells by cytotoxic T lymphocytes and natural killer cells.

A secretable serine proteinase with highly restricted specificity from cytolytic T lymphocytes inactivates retrovirus-associated reverse transcriptase

TSP-1, a murine T cell specific proteinase, is expressed in cytolytic T lymphocytes and secreted upon their interaction with antigen bearing target cells. In searching for possible extracellular substrates of the enzyme in the physiological environment of cytolytic effector cells, we have investigated the proteolytic activity of TSP-1 on retroviral proteins. It is shown that reverse transcriptase derived from the retrovirus Moloney murine leukemia virus is inactivated by TSP-1 via limited proteolysis. The data suggest the possibility that cytolytic T lymphocytes are able to interfere with retroviral replication by secreting a serine proteinase which degrades viral proteins.

A novel serine proteinase (HuTSP) isolated from a cloned human CD8+ cytolytic T cell line is expressed and secreted by activated CD4+ and CD8+ lymphocytes

A novel proteinase, termed human T cell-associated serine proteinase (HuTSP), has been highly purified from a human CD8+ T lymphocyte clone. By using a panel of chromogenic model peptide substrates the enzyme was found to specifically recognize L-arginine and to cleave Tos-Gly-Pro-Arg-nitroanilide with high efficiency at a pH optimum of 10.5-11. Exposure to class-specific proteinase inhibitors revealed that HuTSP is a serine endopeptidase. The enzyme has a mol. mass of approximately 50 kDa (non-reduced) and of approximately 25-30 kDa (reduced) when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis suggesting HuTSP to be a disulfide-linked dimer. The enzyme is shown to be inducible by lectin in both CD4+ and CD8+ lymphocytes. Moreover, HuTSP was detected in a number of independent CD4+ and CD8+ T cell clones and was found to be released from effector cells upon ligand binding to the CD3-T cell receptor complex.

Granzyme A secretion by normal activated Lyt-2+ and L3T4+ T cells in response to antigenic stimulation

Granzyme A is a serine esterase initially isolated from cytoplasmic granules of cytolytic T cell lines (Masson, D. et al., EMBO J. 1986. 5: 1595). Among normal T lymphocytes activated by allogeneic stimulation it is found in both Lyt-2+ and L3T4+ subsets in comparable amounts. Here we show that normal alloantigen-activated T cells secrete the enzyme specifically when mixed with appropriate stimulator cells. Specific enzyme release is dependent on external calcium and removal of calcium blocks further secretion within a few minutes. Both Lyt-2+ and L3T4+ cells specifically secrete the enzyme with similar rates, and anti-L3T4 and anti-Lyt-2 antibodies block secretion by the responder cells expressing these markers. Anti-LFA-1 antibodies, on the other hand, block secretion by either subset.

The T cell-specific serine proteinase TSP-1 is associated with cytoplasmic granules of cytolytic T lymphocytes

This study describes the localization of the previously purified T cell-specific serine proteinase, termed TSP-1 (M. M. Simon et al., EMBO J. 1986. 5: 3267), within cytoplasmic granules of cytolytic T cell lines (CTLL). Subcellular fractionation of disintegrated CTLL (ruptured by nitrogen cavitation) was accomplished by Percoll density gradient centrifugation of cell lysates (postnuclear supernatant). Individual fractions were tested for proteinase activity on chromogenic peptide substrates and for the presence of TSP-1 by Western blot analysis. In addition, each fraction was assayed for cytolytic activity against sheep red blood cells (SRBC), for protein and for additional marker enzymes to assess the enrichment for cellular organells. All serine enzyme-type molecules including TSP-1 expressed by CTLL were identified by labeling cell lysates or gradient fractions with the serine proteinase-specific affinity ligand tritiated diisopropyl fluorophosphate [( 3H]DFP) in the presence or in the absence of class-specific or enzyme-specific proteinase inhibitors and subsequent sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The data demonstrate that the Percoll gradient fraction, which was shown by morphological examination in the electron microscope to be highly enriched for cytoplasmic granules, also contained greater than 80% of proteinase activity in addition to the granule-associated structures cytolysin and arylsulfatase. The identity of the granule-associated proteinase in two independent cell lines, CTLL HY3-Ag3 and CTLL 1.D.9, with the serine proteinase TSP-1 is indicated by its specificity for the chromogenic substrate H-D-Pro-Phe-Arg-p-nitroanilide, its sensitivity to class-specific as well as TSP-1-specific enzyme inhibitors and by its reactivity with a polyvalent TSP-1-specific rabbit antiserum. Both CTLL contain a [3H]DFP-labeled protein that migrates with a molecular mass of 60 kDa under nonreducing conditions and with 30 kDa under reducing conditions and which can be inactivated by the TSP-1-specific inhibitor H-D-Pro-Phe-Arg-chloromethylketone. CTLL HY3-Ag3 (a long-term culture CTLL with natural killer-like activity) but not CTLL 1.D.9 (an antigen-specific short-term cultured CTLL) express in addition a further [3H]DFP-binding protein which migrates with 27 kDa under nonreducing or reducing conditions. No substrate specificity was found for this molecule. The possible function of the granule-associated serine proteinase TSP-1 is discussed.