A study of intermediates involved in the folding pathway for recombinant human macrophage colony-stimulating factor (M-CSF): evidence for two distinct folding pathways

The folding pathway for a 150-amino acid recombinant form of the dimeric cytokine human macrophage colony-stimulating factor (M-CSF) has been studied. All 14 cysteine residues in the biologically active homodimer are involved in disulfide linkages. The structural characteristics of folding intermediates blocked with iodoacetamide reveal a rapid formation of a small amount of a non-native dimeric intermediate species followed by a slow progression via both monomeric and dimeric intermediates to the native dimer. The transition from monomer to fully folded dimer is complete within 25 h at room temperature at pH 9.0. The blocked intermediates are stable under conditions of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and thus represent various dimeric and folded monomeric species of the protein with different numbers of disulfide bridges. Peptide mapping and electrospray ionization mass spectrometry revealed that a folded monomeric species of M-CSF contained three of the four native disulfide bridges, and this folded monomer also showed some biological activity in a cell-based assay. The results presented here strongly suggest that M-CSF can fold via two different pathways, one involving monomeric intermediates and another involving only dimeric intermediates.

Induction of alpha v beta 3 integrin-mediated attachment to extracellular matrix in beta 1 integrin (CD29)-negative B cell lines

beta 1 integrin containing complexes have been implicated as the primary adhesion structures in many lymphocyte extracellular matrix (ECM) interactions. However, many B lymphocytes lack surface expression of the beta 1 subunit, implying that this subpopulation of lymphoid cells must employ alternate adhesion structures if they are to maintain an interactive capacity with ECM. An examination of the adherence properties of the beta 1 integrin-negative B cell line JY indicated that these cells exhibit little or no basal adherence to any of the ECM components examined. However, these cells could be induced to adhere to the ECM components fibronectin, laminin, and vitronectin following treatment with PMA. Blocking studies with monoclonal antibodies indicated the alpha v beta 3 integrin complex was involved in the attachment to each of these ligands. However, the adherence to fibronectin displayed a complex pattern of inhibition suggesting the involvement of other ECM receptors. The utilization of the alpha v beta 3 complex was not unique to the JY cell line. Other B cell lines were observed to employ alpha v beta 3, and these lines similarly lacked expression of beta 1 integrin. These results indicate that alpha v beta 3 can act as a lymphoid ECM-adhesion structure which may provide an alternative means for lymphocytes to interact with ECM. Furthermore, these studies provide evidence for the presence of lymphoid-associated alpha v beta 3 integrins with regulatable activity, which contrasts with the constitutive adhesive potential of these complexes when present on other cell types.

Reactivity of gamma delta T cells induced by the tumour cell line RPMI 8226: functional heterogeneity of clonal populations and role of GroEL heat shock proteins

The human tumour cell lines RPMI 8226 and Daudi are potent inducers of V gamma 9-expressing T cells. The inducing element of RPMI 8226 has not been defined but evidence suggests that a member of the GroEL heat shock protein (HSP) family (HSP 58) may have a role in the induction by Daudi cells. The present study examined the reactivity patterns of gamma delta T-cell clones generated in response to RPMI 8226 and addressed the possible role of HSP 58 in this process. RPMI 8226 induced a population of V gamma 9 TCR+ cells which were heterogeneous in terms of their cell surface markers, patterns of proliferation and cytotoxic responses. All clones expressed CD3, CD2, CD18 and CD29. They demonstrated variability in expression of CD56, CD8 and HLA-DR. RPMI 8226 stimulated proliferation in purified bulk gamma delta cultures and clones. Daudi was also capable of inducing these cells to proliferate while mycobacterial products were not effective. The clones demonstrated a limited non-MHC-restricted cytotoxicity pattern with some evidence of clonal heterogeneity. Although both Daudi and RPMI 8226 were sensitive to lysis by the clones, cold inhibition experiments indicated differential activity towards these targets. Anti-HSP 58 was inhibitory to gamma delta T-cell induction by RPMI 8226, Daudi and mycobacterial products. However, the anti-HSP 58 antibody appears to bind to the surface of at least six different tumour cell lines with no correlation to their ability to induce gamma delta T cells and the anti-HSP 58 inhibited non-gamma delta responses.

Prolonged expression of high molecular mass CD45RA isoform during the differentiation of human progenitor thymocytes to CD3+ cells in vitro

CD45, the leukocyte common Ag, has been shown to characterize T cell development both within the thymus and among peripheral T cells. The work reported here demonstrates that human multinegative (MN) thymocytes, depleted of cells bearing CD3, CD4, CD8, and CD19, express predominantly the high molecular mass CD45RA isoform, and lack low molecular mass CD45RB isoforms and CD45R0 as detected by immunofluorescence. By immunoprecipitation of surface-labeled CD45 molecules from MN thymocytes, a proportion of the CD45 is in fact of low molecular mass but does not include epitopes recognized by CD45R0, nor by CD45RB mAb specific for the p190. This suggests either glycosylation variants of CD45RB/CD45R0 undetectable by our mAb, or underglycosylated CD45RA. MN thymocytes lack TCR-alpha beta mRNA confirming their early developmental stage. Upon culture with IL-2 or with mitogenic combinations of anti-CD2/CD28 mAb, MN thymocytes differentiate to acquire CD3, TCR-alpha beta, and in some cases CD4 and/or CD8. We have predicted that maintenance of CD45RA and lack of CD45R0 expression is fundamental to generative thymic development. If correct, this demands that unlike peripheral T cells, differentiation of MN thymocytes should be accompanied by prolonged expression of high molecular mass CD45 isoforms. Analysis of CD45 isoform expression during MN thymocyte development confirms this prediction and indicates that expression of CD45RA is maintained, at increasing density, for at least 8 to 12 days of culture. Unlike peripheral blood T cells, this is accompanied by the gradual acquisition of firstly the p190 isoforms of CD45RB and later by CD45R0, resulting in a population of CD3+TCR-alpha beta cells coexpressing CD45RA/RBp190/R0. Dot blot analysis of mRNA from differentiating MN thymocytes indicates prolonged expression of mRNA encoding CD45 exons a, b, and c, again in contrast to peripheral T cells which lose all mRNA for alternatively spliced CD45 exons within the first 24 h poststimulation. This is discussed in the context of negative selection during thymic development and interconversion of T cell subsets.

Prolonged expression of high molecular mass CD45RA isoform during the differentiation of human progenitor thymocytes to CD3+ cells in vitro

CD45, the leukocyte common Ag, has been shown to characterize T cell development both within the thymus and among peripheral T cells. The work reported here demonstrates that human multinegative (MN) thymocytes, depleted of cells bearing CD3, CD4, CD8, and CD19, express predominantly the high molecular mass CD45RA isoform, and lack low molecular mass CD45RB isoforms and CD45R0 as detected by immunofluorescence. By immunoprecipitation of surface-labeled CD45 molecules from MN thymocytes, a proportion of the CD45 is in fact of low molecular mass but does not include epitopes recognized by CD45R0, nor by CD45RB mAb specific for the p190. This suggests either glycosylation variants of CD45RB/CD45R0 undetectable by our mAb, or underglycosylated CD45RA. MN thymocytes lack TCR-alpha beta mRNA confirming their early developmental stage. Upon culture with IL-2 or with mitogenic combinations of anti-CD2/CD28 mAb, MN thymocytes differentiate to acquire CD3, TCR-alpha beta, and in some cases CD4 and/or CD8. We have predicted that maintenance of CD45RA and lack of CD45R0 expression is fundamental to generative thymic development. If correct, this demands that unlike peripheral T cells, differentiation of MN thymocytes should be accompanied by prolonged expression of high molecular mass CD45 isoforms. Analysis of CD45 isoform expression during MN thymocyte development confirms this prediction and indicates that expression of CD45RA is maintained, at increasing density, for at least 8 to 12 days of culture. Unlike peripheral blood T cells, this is accompanied by the gradual acquisition of firstly the p190 isoforms of CD45RB and later by CD45R0, resulting in a population of CD3+TCR-alpha beta cells coexpressing CD45RA/RBp190/R0. Dot blot analysis of mRNA from differentiating MN thymocytes indicates prolonged expression of mRNA encoding CD45 exons a, b, and c, again in contrast to peripheral T cells which lose all mRNA for alternatively spliced CD45 exons within the first 24 h poststimulation. This is discussed in the context of negative selection during thymic development and interconversion of T cell subsets.

B lymphocyte fibronectin receptors: expression and utilization

Lymphocytes adhere to fibronectin (FN) via multiple receptors of the VLA (beta 1, CD29 integrin) family. The cellular requirement for the variety of FN receptors (FNR) which have been described is unclear, but they may be associated with differential signalling processes, cooperative effects which may stabilize cellular attachment, or cell homing and retention processes. The present study was undertaken to examine the FN adherence properties and receptor utilization patterns of human B cells. Of ten B-cell culture lines which were studied, six demonstrated a significant adherence to FN. Among these, four employed alpha 4 beta 1, (CD49d/29) and two employed alpha 4 beta 1/alpha 5 beta 1, (CD49d/29, CD49e/29). There was no apparent correlation between the differentiation status of the lines and their FNR utilization patterns. Furthermore, expression of FNR alone was not sufficient to confer FN binding potential. Freshly isolated tonsil B cells did not display significant adherence to FN. Following stimulation, a marked increase in VLA antigens was observed, and the capacity to attach to FN-coated surfaces was co-acquired. Analysis of the induced bulk B-cell population demonstrated that both alpha 4 beta 1 and alpha 5 beta 1 were used for adherence. These results clearly indicate that activated B cells, similar to T cells, may express and utilize alpha 5 beta 1 as a FNR.

Beta 1 integrin-mediated lymphocyte adherence to extracellular matrix is enhanced by phorbol ester treatment

The interaction of the human T cell leukemia, Jurkat, with the extracellular matrix components collagen and fibronectin was examined. These cells displayed constitutive binding to fibronectin and low levels of adherence to collagen which were enhanced following stimulation with phorbol esters. The relevant binding structures were identified as members of the CD29/beta 1 integrin family of adhesion molecules. Adherence to collagen and to fibronectin was mediated by alpha 2 beta 1 and alpha 5 beta 1, respectively. The enhancement of adherence by phorbol esters did not involve up-regulation of receptor expression but appeared to derive from the increased functionality of structures which were expressed on the cell surface.

Lymphocyte extracellular matrix interactions. Induction of interferon by connective tissue components

Limiting dilution analysis was performed in the presence of interleukin 2 (IL-2) on lymphocytes isolated from the synovial fluid (SF) and peripheral blood (PB) of patients with rheumatoid arthritis (RA) and PB of normal donors. Clones of these 'spontaneously' IL-2-responsive cells from PB and SF were compared for their reactivity with components of the extracellular matrix (i.e. native or denatured type I or type II collagen and proteoglycan). It was determined that all clones from both PB and SF were activated to produce interferon (IFN) in the presence of any of the connective tissue components (CTC). Clones derived from normal PB behaved in a similar fashion but produced lower IFN-gamma levels. There was a synergy between the CTC and serum or plasma fibronectin, which was more apparent when soluble CTC were used as the stimuli rather than immobilized CTC. The fibronectin alone was unable to induce IFN-gamma production under any of the conditions tested (i.e. soluble or immobilized). These results demonstrate that clones of IL-2-responsive T cells can be activated by interactions with connective tissue components to produce IFN-gamma.

Interleukin 2 responsive T cell clones from rheumatoid and normal subjects: proliferative responses to connective tissue elements

In vivo-activated interleukin 2 responsive T cell clones were generated from peripheral blood (PB) and synovial fluid (SF) of rheumatoid arthritis (RA) patients and from normal control PB. The specificity of these clones was assessed by measuring proliferation induced by the connective tissue elements (CTE) collagen types I and II, native and denatured, proteoglycans, and irrelevant control antigens. The cloned T cells from RA patients but not from normal subjects responded in vitro with proliferation to all CTE but not to control antigens purified protein derivative, ovalbumin, or lysozyme. Proliferation occurred in the presence and absence of accessory cells (AC), but the responses were consistently higher in the presence of AC. Antibodies to HLA-DR abrogated the proliferative response to CTE suggesting that DR expression was necessary for the induction of proliferation. These findings demonstrate the existence of clonable T cells responsive to CTE in PB and SF of RA patients. Expression of reactivity to CTE may contribute to the chronicity of the inflammation in RA.

Fibroblast-activating factor production by interleukin (IL)-2 dependent T-cell clones from rheumatoid arthritis patients and normal donors

T cells spontaneously responsive to interleukin (IL)-2 were cloned from the peripheral blood (PBL) or synovial fluid (SFL) lymphocyte populations obtained from patients with rheumatoid arthritis (RA) or from normal PBL. The clones were compared for their capacities to produce fibroblast-activating factors (FAFs) which support the growth of RA synovial fibroblasts. Clones derived from all sources produced FAFs following mitogen stimulation, but SFL clones synthesized significantly higher levels of FAF activity. Physicochemical characterization of the FAFs suggested that SFL- and PBL-derived clones produced similar factors. It was also demonstrated that interferon-gamma and IL-2 did not contribute to the FAF activity of the clone supernatants. These results demonstrate that a subpopulation of activated lymphocytes which are present in increased numbers in the rheumatoid joint can produce factors which influence rheumatoid synovial cell growth.

Lymphokine production in rheumatoid arthritis and systemic lupus erythematosus

The production of interferon (IFN) by peripheral blood lymphocytes from patients with rheumatoid arthritis (RA) and of IFN and interleukin 2 (IL-2) in systemic lupus erythematosus (SLE) was compared with that of healthy controls. Patients with SLE showed a significant reduction in IL-2 production compared to controls if the PBL were irradiated before mitogen stimulation. No patient with RA or SLE studied had impaired IFN production regardless of disease activity and the IFN produced was always IFN-gamma in type. We conclude that there is an abnormality in IL-2 production in SLE but there is no abnormality in IFN-gamma production in either RA or SLE.

Characterization of IL-2 responsive synovial T lymphocytes in rheumatoid arthritis. II. Functional properties

Lymphocytes from peripheral blood (PBL) and synovial fluid (SFL) were obtained from patients with rheumatoid arthritis (RA) and cloned under limiting-dilution conditions without prior activation but in the presence of exogenous interleukin (IL)-2. The precursor frequencies of such in vivo activated IL-2-responsive cells were higher in RA SFL (1/83) than in RA PBL (1/201) or normal PBL (1/377). These HLA-Dr/Ia-positive clones expressed T-cell markers CD3 and T101 and were either CD4- or CD8-positive but lacked NK markers CD11, CD16, and HNK-1. All such clones were cytotoxic for NK-sensitive K562 targets and NK-insensitive Raji cell targets. These cells, which most closely resemble nonmajor histocompatibility complex (MHC) restricted cytotoxic T (CTL) cells, are present with increased frequency in RA synovial fluids.

Specific interaction of vinculin with alpha-actinin

Vinculin and alpha-actinin are cytoskeletal proteins present at focal contacts of the ventral surface of cultured fibroblasts. We labelled alpha-actinin with an acceptor fluorophore and vinculin with a donor. A mixture of vinculin and alpha-actinin showed a 28% quench, due to energy transfer, suggesting an interaction. Quench of vinculin was dependent on the concentration of alpha-actinin; Scatchard analysis gives a dissociation constant in the microM range. Quench was inhibited by excess unlabelled alpha-actinin, and by reaction of the acceptor protein with p-chloromercuribenzoate. We found that vinculin had a slightly greater elution volume in a gel filtration column equilibrated with alpha-actinin, indicating a higher effective Stokes radius due to the interaction of the two proteins.

Studies on proteins that co-purify with smooth muscle vinculin: identification of immunologically related species in focal adhesions of nonmuscle and Z-lines of muscle cells

Membrane extracts from chicken smooth muscle contain, along with filamin, vinculin and alpha actinin, a group of polypeptides that have the ability to interact with the "barbed end" of actin filaments. These low molecular mass polypeptides were designated as HA1 (Wilkins, J.A., and S. Lin, 1986, J. Cell Biol., 102:1085-1092). In this study, polyclonal antibodies raised against the HA1 preparation were used to study the cellular localization and tissue distribution of these polypeptides. Immunofluorescence experiments revealed a primary localization of staining at the ends of stress fibers on the ventral surface of cultured chicken embryo fibroblasts, i.e., those areas known as the focal adhesions. Specific staining was also seen at the Z-lines of both skeletal muscle myofibrils and cultured embryonic heart cells. Immunoblotting analyses of proteins from different tissues prepared to avoid proteolytic degradation showed a much different pattern than that of HA1 itself. Immunoreactive polypeptides with reduced molecular masses of 200,000 and 150,000 D were found in smooth muscle and fibroblasts while 200 and 60 kD polypeptides were found in cardiac muscle tissue. The antibodies recognized 60- and 31-kD polypeptides on immunoblots of chicken breast muscle. The results from this study strongly suggest that the polypeptides in HA1 arose from proteolysis of high molecular mass molecules. The studies also raise the possibility that immunologically related proteins in muscle and nonmuscle cells may be involved in linking actin filaments to Z-lines and membranes, respectively.

Characterization of synovial T lymphocytes in rheumatoid arthritis. I. Production of IL-2 dependent T cell clones from synovial fluid and peripheral blood

Lymphocytes obtained from the peripheral blood (PBL) or synovial fluids (SFL) of patients with rheumatoid arthritis (RA) or other inflammatory joint diseases were compared with the PBL from normal individuals, by cloning under limiting dilution conditions in the presence of interleukin 2 (IL-2). The precursor frequency estimates of IL-2 responsive cells from these sources did not differ appreciably. However there were marked differences in the surface marker phenotypes of the clones derived from the PBL as compared to SFL. There was a predominance of OKT4-8+ cells in SFL from RA and non RA donors with inflammatory joint disease while PBL from all sources showed a marked prevalence of OKT4+8- cells. Comparison of precursor frequencies in the presence of PBL and SFL indicated that there were variations in the capacities of the SFL and PBL IL-2 dependent cells to grow on these fillers. SFL derived cells grew equally well on PBL or SFL filler, while PBL clones grew efficiently only on PBL fillers. Collectively these results indicate that there are marked differences in the surface phenotypes and growth requirements of IL-2 responsive SFL as compared to PBL.

Biochemical changes induced in hairy-cell leukemia following treatment with the adenosine deaminase inhibitor 2'-deoxycoformycin

The adenosine deaminase inhibitor 2'-deoxycoformycin and interferon are highly effective in the treatment of hairy-cell leukemia. In this study, a patient with type 2 hairy-cell leukemia was treated with one cycle of 2'-deoxycoformycin (4 mg/m2, i.v. weekly for 3 weeks), which was repeated at 9 wk. No toxicity was observed, and the hairy cell count fell from 72,000/mm3 to 5,000/mm3 in 3 mo, with a concomitant 50% decrease in the spleen size. The erythrocyte deoxyadenosine triphosphate content increased to 13.6 pmol/10(6) cells following the initial three weekly treatments, but there was no decrease in the adenosine triphosphate pool size and no evidence of hemolysis. The hairy cell adenosine deaminase activity was inhibited by greater than 95% 24 h following the first 2'-deoxycoformycin injection and returned to the pretreatment value at Day 8, although there was a linear decline in peripheral hairy cell count (50%) during this period. No ultrastructural changes were observed in the hairy cells following 2'-deoxycoformycin to suggest lymphocytotoxicity or cellular differentiation. The antitumor activity of 2'-deoxycoformycin could not be attributed to alterations in the hairy cell deoxyadenosine triphosphate/adenosine triphosphate levels or to the induction of DNA strand breaks. Additionally, the plasma levels of interferon did not change during therapy, making it unlikely that 2'-deoxycoformycin exerts its activity by inducing endogenous interferon synthesis.

A re-examination of the interaction of vinculin with actin

Vinculin prepared by published procedures (i.e., Feramisco, J. R., and K. Burridge, 1980, J. Biol. Chem., 255:1194-1199) contains contaminants that have been shown by Evans et al. (Evans, R. R., R. M. Robson, and M. H. Stromer, 1984, J. Biol. Chem., 259:3916-3924) to reduce the low-shear viscosity of F-actin solutions. In this study we separated contaminants from conventional vinculin preparations by hydroxylapatite chromatography. We found that although the contaminants represented a small fraction (less than or equal to 5%) of the total protein in the conventional vinculin preparations, they were responsible for practically all of the filament capping and bundling activities previously attributed to vinculin. In addition, we examined the size of the molecule(s) responsible for the observed capping activity and found that its apparent molecular weight under denaturing conditions in sodium dodecyl sulfate (SDS) polyacrylamide gels fell within a broad range of 23,000-33,000. These results contrast with the observation that under nondenaturing conditions, the activity migrated in gel filtration columns at a position that corresponded to the Stoke's radius of a much bigger molecule. Since the migration of the activity in these chromatographic experiments is independent of the presence of vinculin, it is unlikely that the active protein associates with vinculin with high affinity under the conditions examined.

Interleukin 2 production and responsiveness in active and inactive rheumatoid arthritis

The interleukin 2 (IL-2) production and responsiveness of peripheral blood lymphocytes from patients with rheumatoid arthritis (RA) with active or inactive disease was compared with that of normal control donors. IL-2 production was assessed using a cellular interleukin assay in which an IL-2 dependent cell line was cocultured with varying numbers of irradiated IL-2 producing lymphocytes from the different donor sources. Cells from patients with active disease showed a significantly different pattern of IL-2 production from that of control or inactive RA patients in that a lower number of cells supported growth of the IL-2 dependent cell line. In one patient this shift in pattern was shown to correlate with change in disease activity. Lymphocyte responsiveness to IL-2 as determined by limiting dilution analysis did not differ significantly between the different groups. The results are consistent with a hyperproduction of IL-2 in RA during active disease.

OKT4:OKT8 ratios of circulating T cells and in vitro suppressor cell function of patients with juvenile rheumatoid arthritis (JRA)

OKT4:OKT8 ratios of circulating T cells and in vitro suppressor cell function of patients with juvenile rheumatoid arthritis (JRA) were studied and correlations were made with clinical characteristics and laboratory variables of disease activity. Suppression of pokeweed mitogen induced immunoglobulin synthesis by OKT4+ and OKT8+ cells was taken as a measure of suppressor cell function. Mean values of OKT4:OKT8 ratios were increased in patients with JRA. A decrease in suppressor cell function correlated with high OKT4:OKT8 ratios but neither abnormality was related to increased disease activity.

Tumor-activated NK cells trigger monocyte oxidative metabolism

We have examined the hypothesis that tumor cells can stimulate a respiratory burst by human natural killer (NK) cells in vitro as measured by luminol-dependent chemiluminescence (CL). Percoll-purified NK cells, containing 40% HNK-1+ cells and less than 1 to 4% esterase-positive contaminating monocytes, can generate a strong CL response after stimulation with the NK-susceptible K562 tumor but not with the NK-resistant P815 tumor cells. Although the response was NK dependent, as shown by depletion with NK-directed monoclonal antibodies (HNK-1, OKT-11, and OKM-1), the cell generating the CL response was not the NK cell. On the basis of several independent experimental approaches the CL response always required the presence of monocytes in the NK preparation. a) Treatment with a monocyte-specific monoclonal antibody (MO2) and complement completely abolished CL. b) The cells producing the CL response were strongly adherent to nylon wool columns (NWC), and large granular lymphocyte preparations containing less than 0.1% esterase-positive cells were inactive. c) NK cells cultured in IL 2-containing medium and tested over several days did not generate CL. d) Optimal numbers of monocytes (less than 1 to 2%) added to a non-CL NWC-purified NK population restored CL, whereas larger or smaller amounts were ineffective. Neither these procedures nor the addition of superoxide dismutase (which completely blocked CL) had any effect on NK lytic activity. We subsequently demonstrated that a factor present in supernatants obtained from NK/K562 incubations, but not from NK or tumor cells alone, could stimulate monocyte CL. We therefore propose that the CL response measured in NK-enriched Percoll fractions originated from contaminating monocytes that were triggered by factor(s) released from tumor-activated NK cells, and that superoxide anion was not required for NK lysis.

Tumor-activated NK cells trigger monocyte oxidative metabolism

We have examined the hypothesis that tumor cells can stimulate a respiratory burst by human natural killer (NK) cells in vitro as measured by luminol-dependent chemiluminescence (CL). Percoll-purified NK cells, containing 40% HNK-1+ cells and less than 1 to 4% esterase-positive contaminating monocytes, can generate a strong CL response after stimulation with the NK-susceptible K562 tumor but not with the NK-resistant P815 tumor cells. Although the response was NK dependent, as shown by depletion with NK-directed monoclonal antibodies (HNK-1, OKT-11, and OKM-1), the cell generating the CL response was not the NK cell. On the basis of several independent experimental approaches the CL response always required the presence of monocytes in the NK preparation. a) Treatment with a monocyte-specific monoclonal antibody (MO2) and complement completely abolished CL. b) The cells producing the CL response were strongly adherent to nylon wool columns (NWC), and large granular lymphocyte preparations containing less than 0.1% esterase-positive cells were inactive. c) NK cells cultured in IL 2-containing medium and tested over several days did not generate CL. d) Optimal numbers of monocytes (less than 1 to 2%) added to a non-CL NWC-purified NK population restored CL, whereas larger or smaller amounts were ineffective. Neither these procedures nor the addition of superoxide dismutase (which completely blocked CL) had any effect on NK lytic activity. We subsequently demonstrated that a factor present in supernatants obtained from NK/K562 incubations, but not from NK or tumor cells alone, could stimulate monocyte CL. We therefore propose that the CL response measured in NK-enriched Percoll fractions originated from contaminating monocytes that were triggered by factor(s) released from tumor-activated NK cells, and that superoxide anion was not required for NK lysis.

Generation of interleukin-2-dependent T cell lines from synovial fluids in rheumatoid arthritis

Synovial fluids from rheumatoid arthritis (RA) patients were found to contain activated T lymphocytes that could be maintained as continuous T cell lines (CTCL) in the presence of the T cell growth factor, interleukin (IL)-2. The CTCL predominantly expressed the OKT8 phenotype and were Ia antigen positive. IL-2-dependent RA CTCL could be maintained in an active dividing state by the presence of RA synovial fluids, whereas IL-2-dependent CTCL from mitogen stimulated PBL failed to respond to the fluids, which were shown to contain IL-2. This suggested that RA CTCL exhibit unique properties not possessed by normal PBL CTCL. The CTCL generated from activated synovial T lymphocyte populations in RA may be used to assess the functions of these cells and their responses to regulatory factors.

The production of immunoregulatory factors by a human macrophage-like cell line. III. The relationship between the lymphoid-specific inhibitor of DNA synthesis and gamma-interferon

Mitogenic stimulation of sublines of the human histiocytic lymphoma, U937, results in the production of an inhibitor of lymphocyte proliferation (IDS-U937). The relationship of IDS-U937 to alpha- and gamma-interferon was examined by several techniques: (1) the antiviral activity of the IDS preparations was determined, (2) the effects of antibodies to interferon on IDS activities, and (3) the comparison of the antiproliferative activities of gamma-IFN and IDS. The relationship of IDS to other macrophage derived inhibitors is also discussed with respect to target cell specificities and modes of action.

Brevin, a serum protein that acts on the barbed end of actin filaments

It has previously been shown that brevin, a relatively abundant serum protein, inhibits salt-induced polymerization of actin and reduces the length of actin filaments in vitro. In this study, we find that in the presence of calcium, brevin inhibits actin polymerization that has been nucleated by spectrin-band 4.1-actin complex from erythrocytes. Brevin also blocks elongation of actin filaments from reconstituted inside-out erythrocyte ghosts. Thus, brevin resembles the cytochalasins in inhibiting actin filament elongation by binding to the rapidly growing end of actin filaments (the barbed end after heavy meromyosin decoration). Brevin, like gelsolin from macrophages and villin from intestinal brush border, also appears capable of severing preformed actin filaments and disrupting filament networks as measured with a low-shear falling ball viscometer.