Protease activity of normal and PHA stimulated human lymphocytes

An assay measuring the release of TCA soluble radioactive peptides from ³H acetylated casein or hemoglobin has been used to demonstrate that human peripheral blood lymphocytes contain a number of proteases, including cathepsin D, a neutral serine protease(s) inhibited by DFP and TLCK and probably a thiol protease(s) as well. We have also found a neutral protease activity bound to the surface of the lymphocyte, but not secreted into the medium which is not inhibited by TLCK. TLCK inhibits blast transformation to PHA under conditions that do not profoundly affect protein synthesis and inhibits the total extractable proteolytic activity of lymphocytes by approximately 25%. Lymphocytes contain one or more proteases that may play a role in blast transformation and other lymphocyte functions.     

Effect of cyclosporin A on human lymphocyte responses in vitro. III. CsA inhibits the production of T lymphocyte growth factors in secondary mixed lymphocyte responses but does not inhibit the response of primed lymphocytes to TCGF

The mechanism whereby Cyclosporin A (CsA) inhibits secondary mixed lymphocyte responses was assessed. CsA added to secondary MLR cultures inhibited proliferation and induction of cytolytic lymphocyte activity. This inhibition was found to be associated with the inhibition of T lymphocyte stimulating growth factor(s) (TCGF) production in the supernatants of secondary MLR cultures. As little as 1.0 micrograms/ml of CsA added to secondary MLR cultures resulted in no measurable TCGF activity. In contrast, moderate doses of CsA (1.0, 2.5 micrograms/ml), which completely inhibited the secondary MLR response to alloantigen, did not inhibit the proliferative and CML response of alloantigen-primed lymphocytes to these stimulating growth factors. Even at high doses of CsA (20 micrograms/ml), substantial levels of proliferation (50% of control response) and CML induction (60% of control response) were observed when the primed cells were exposed to secondary MLR supernatants containing TCGF activity. It was concluded that inhibition of secondary mixed lymphocyte responses by CsA may be due in part to the inhibition of TCGF production rather than the inhibition of the effect of TCGF on mature cytotoxic T lymphocytes.     

Immunosuppressive activity of murine newborn spleen cells. I. Selective inhibition of in vitro lymphocyte activation.

Cell-mediated immune responses to newborn lymphocyte alloantigens were investiated using mitogen activation, mixed lymphocyte reaction (MLR) and cell-mediated lympholysis (CML). Spleen cells from 1- to 5-day-old (C57BL/6 × Balb/c) F₁ mice co-cultured with maternal strain (BALB/c) splenocytes did not affect DNA synthesis of maternal strain cells in the presence of concanavalin A or phytohemagglutinin. Newborn cells did inhibit the lipopolysaccharide response of maternal strain lymphocytes and these cells also depressed DNA synthesis when added to MLR cultures of BALB/c and C57BL/6 spleen cells. Newborn cells expressed poor stimulatory capacity in semiallogeneic MLR and also caused marked inhibition of DNA synthesis when added to semiallogeneic MLR containing BALB/c (responder) and CB6F₁ adult splenocytes (stimulator). The suppression of MLR by neonatal cells persisted for the first 2 weeks of life and was associated with a soluble factor released during culture. The suppressive activity was almost completely abrogated after depleting the T-cells from newborn splenocytes. However, these same cells did not interfere with the in vitro generation of cytotoxic lymphocytes in the CML assay. The selective immunosuppressive properties of newborn spleen cells may be important during pregancy by protecting the immunologically alien fetus from rejection by the mother.     

The effects of electrophoretically "slow" and "fast" alpha-2 macroglobulin on mixed lymphocyte cultures

It has been determined that alpha-2 macroglobulin (alpha 2M) is more suppressive of a mixed lymphocyte response (MLR) when complexed with proteinase than in its "native" state. Other alpha 2M preparations showed a moderate level of MLR suppression, but it is unlikely that this is a result of interaction with cellular proteinases. A panel of other proteinase inhibitors (alpha 1 PI, SBTI, BPTI, TLCK) did not suppress the MLR to the same extent as alpha 2M either when bound with or free from trypsin. A dose-responsive pattern of MLR suppression similar to that observed with purified proteinase-complexed alpha 2M was seen with serum containing proteinase-complexed alpha 2M. The population of cells that apparently conveys the suppressive property is the adherent cells (putative monocytes), which can reduce the MLR almost as well as unfractionated cells when exposed to alpha 2M. Most of these properties of alpha 2M were demonstrable in "serumless" medium with qualitative similarity to the MLR obtained in cultures performed with conventional serum supplemented medium. It was found that alpha 2M-trypsin complexes must be presented at or near culture initiation and remain in contact with the cells for a minimum of approximately 4 hr to have its optimum effect.     

Interactions between neuropeptides and dexamethasone on the mitogenic response of rabbit spleen lymphocytes.

The interactions between vasoactive intestinal peptide (VIP), substance P (SP), a somatostatin analog (SMS 201-995) and dexamethasone have been investigated on the Con A mitogenic response of rabbit spleen cells. The neuropeptide regulatory effects appeared to be time dependent: when added with the Con A mitogen, they inhibited (VIP) or did not modulate (SMS and SP) the rabbit lymphocyte proliferation and did not change the inhibitory effect induced by a dexamethasone preincubation. When added 18 h before the mitogen, they all induced an increase of the proliferative response at high concentration. The mitogenic response observed when adding dexamethasone to lymphocytes previously preincubated in the presence of neuropeptides was not different from control response except with SMS 10(-10) M. The similar lymphocyte responses obtained whatever the neuropeptide suggested that the immunomodulatory effect induced by a neuropeptide preincubation might be mediated by the induction of common effector(s).     

Studies on the regulation of lymphocyte reactivity by normal and activated macrophages.

To determine the potential role of macrophages as regulators of the immune response, the effect of mouse peritoneal macrophages on transforming mouse spleen lymphocytes was investigated. Mitogen and antigen stimulated lymphocyte transformation, as measured by DNA synthesis, was enhanced by all concentrations of normal macrophages tested, but only by low concentrations of activated macrophages. High concentrations of activated macrophages markedly inhibited lymphocyte transformation. This inhibition occurred whether lymphocyte DNA synthesis was measured by incorporation of [³H]TdR or of ³²P. Activated macrophages cultured with lymphocytes within 4 hr of being removed from the peritoneal cavity inhibited lymphocyte transformation. When activated macrophages were cultured alone for 24 or more hours before addition of lymphocytes, enhancement of transformation was noted. Once lymphocytes were exposed to activated macrophages, they could not be induced to undergo transformation in the presence of Con A. Whereas heat-killed activated macrophages, which appeared intact morphologically, lost their capacity to inhibit lymphocyte transformation, macrophages treated with mitomycin C to inhibit DNA synthesis retained this capacity. Syngeneic and allogeneic macrophages had similar inhibitory ability. Supernatants from cultures of many cell types (including normal or activated macrophages, lymphocytes, lymphocytes plus macrophages, and L cells) inhibited [³H]TdR incorporation by both mitogen stimulated lymphocytes and tumor cells. These studies demonstrate the capacity of macrophages to regulate lymphocyte transformation in vitro and suggest a role for these cells as regulators of cell-mediated immunity in vivo.     

Inhibition of the transformation-specific kinase in ASV-transformed cells by N-alpha-tosyl-L-lysyl chloromethyl ketone.

We find that the protease inhibitor N-α-tosyl-L-lysyl chloromethyl ketone (TLCK) inhibits the transformation-specific kinase activity (Collett and Erikson, 1978) associated with p60^src, the avian sarcoma virus (ASV) gene product responsible for the transformation of fibroblasts. TLCK has been shown to induce the phenotypic reversion of ASV-transformed cells to normal (Weber, 1975). Kinase activity was measured in extracts of chick embryo fibroblasts (CEF) transformed by the Schmidt-Ruppin strain of ASV (SR-ASV) with antiserum from rabbits bearing ASV-induced tumors. The immunoprecipitates were incubated with γ-³²P-ATP under conditions in which the phosphorylation of the IgG heavy chain in the immunoprecipitate was directly proportional to the concentration of cell extract. When ASV-transformed CEF were treated with 0.1 mM TLCK, the kinase activity was reduced by 60% after 2 hr and by 80% after 6 hr, and continued to remain low for up to 40 hr when TLCK was present. When TLCK was removed, the kinase activity rose slowly over a period of many hours, suggesting that the enzyme is irreversibly inactivated by TLCK and new enzyme must be synthesized. The effect of TLCK in vivo is concentration-dependent and specific. Other serine protease inhibitors had no effect on kinase activity. At low concentrations (0.03 mM), TPCK produced partial inhibition (≤20%), but at higher concentrations TPCK was extremely toxic to the cells and therefore could not be tested. The inhibition by TLCK was not due to its ability to inhibit protein synthesis since cycloheximide treatment (1 μg/ml) did not significantly reduce kinase activity. TLCK also inhibited kinase activity when added directly to cell extracts, but about 5 times higher concentrations of TLCK were required to produce 50% inhibition. Under these conditions both TLCK and TPCK were comparable inhibitors, whereas PMSF had no effect. Our finding that the inhibition of the kinase by TLCK in vivo parallels the reversion of cell morphology to normal suggests that the kinase has an important role in transformation and offers a biochemical rationale for treatment of tumors with this agent.     

Macrophage-lymphocyte interaction. III. Site of alloantiserum inhibition of T lymphocyte proliferation induced by allogeneic or aldehyde-bearing cells.

Inhibition by anti-Ia sera of guinea pig T lymphocyte proliferation induced by allogeneic macrophages (MLR) and NaIO4 or neuraminidase-galactose oxidase-treated macrophages has been investigated in order to identify the target cell upon which the antisera act. Anti-2 and anti-13 alloantisera were found to inhibit both MLR and aldehydeinduced T cell reactivity when directed against the specificity of the stimulatory macrophage. Little or no inhibition was observed when these antisera were directed against the T lymphocyte specificity when cultures were harvested at the time of peak proliferation. In addition, anti-2 serum was found to inhibit macrophage-lymphocyte rosett formation at 20 hr between neuraminidase-galactose oxidase-treated strain 2 macrophages and strain 13 lymphocytes. These findings demonstrate that inhibition of T cell proliferation can be produced by anti-Ia sera directed against the macrophage and raise the possibility that Ir gene products may function in part at the level of the macrophage.     

Mixed lymphocyte reactions: absence of stimulation by irradiated allogeneic cells

¹³⁷Cs-irradiated mouse spleen cells, in contrast to mitomycin-blocked cells, do not stimulate a mixed lymphocyte reaction (MLR) when cocultured with normal allogeneic lymphocytes. Attempts to find an irradiation dose which blocks the DNA-synthetic capability of alloantigenic cells, but which does not also render them unstimulatory in mixed cultures, have not been successful. Low-level irradiation (100–500 rad) does not completely block mitogen (PHA) reactivity, hence the target cells may be capable of participating in a two-way MLR. High-level irradiation (> 1000 rad), however, thoroughly blocks PHA-stimulated DNA synthesis and eliminates the capacity of these cells to stimulate an MLR. Potentiation of MLR by irradiated cells syngeneic with the reacting cell population was not possible in these experiments. Cell death and lysis in irradiated suspensions occurred during the 72-hr culture period. It is believed that a combination of cell lysis and irradiation-blocked metabolic events normally necessary for the MLR sufficies to explain the poor or nonexistent MLR's obtained in these experiments.     

Inhibition of normal allogeneic lymphocyte mitogenesis by a factor released from human tumor cells in culture

Summary Human tumor and normal cell lines in culture were examined for the release of factors capable of inhibiting lymphocyte blastogenesis. Supernatants from tumor cell cultures of melanoma, carcinoma (lung, colon, breast), sarcoma, and normal fibroblasts inhibited normal lymphocyte response to PHA. Only supernatants from the tumor cell lines C1 (colon carcinoma), 734B (breast carcinoma), and 231 (breast carcinoma) were found to inhibit both PHA and ConA responses significantly. The two breast carcinoma cell lines, 734B and 231, which also were capable of inhibiting lymphocyte responses to PPD and alloantigens, were investigated further. The inhibition of lymphocyte blastogenesis caused by the supernatant of these two cell lines could not be overcome by the addition of added mitogen. Further experiments showed that the inhibition was not due to nutrient deficiencies and the supernatants were not directly toxic to the lymphocyte cultures as judged by trypan blue exclusion.     

Lysozyme-induced inhibition of the lymphocyte response to mitogenic lectins

Both human lysozyme (HL) and hen egg white lysozyme (HEWL) inhibited the proliferative response of peripheral blood lymphocytes to T cell mitogens such as the lectins phytohemagglutinin and concanavalin A. This inhibition was observed both when HL or HEWL was added to the lymphocyte cultures in combination with phytohemagglutinin or concanavalin A and when lymphocytes were pretreated with either lysozyme and extensively washed prior to culture with mitogens. Under both conditions, the effects were strictly dose dependent; the lysozyme concentrations yielding maximal inhibitory effect were 5 micrograms/ml for HL and 1 microgram/ml for HEWL, while both lower and higher concentrations were less effective. Specific antilysozyme rabbit sera completely prevented the inhibitory effects of both HL and HEWL on the proliferative response of lymphocytes to phytohemagglutin or concanavalin A. Chitotriose (a lysozyme inhibitor) caused a strong reduction in the inhibitory effects of the two lysozymes on the lymphocyte response to either lectin. HL and HEWL also were found to markedly inhibit the polyclonal B cell proliferation and differentiation induced by pokeweed mitogen and T cells. A less marked inhibition was also obtained when T cells, but not B cells, were pretreated with HL or HEWL. Again, as in the experiments with T cell mitogens, the effects were dose dependent and 5 micrograms/ml HL and 1 microgram/ml HEWL proved to be the most effective concentrations. The possible mechanisms by which lysozyme inhibits the lymphocyte response to mitogenic lectins are considered and discussed. The enzymatic activity seemed to perform an essential function, as shown by the loss of effect when the heat- or trypsin-inactivated lysozymes were used and by the fact that only the enzymatically active compound, among certain semisynthetic derivatives of HEWL, inhibited the lymphocyte response to the mitogens. However, the cationic properties of the lysozyme molecule appeared to be essential too, since enzymes with a similar specificity of action showed effects similar to those observed with HL or HEWL only when they carried a strong positive charge. It is suggested that lysozyme, which is naturally secreted by monocytes and macrophages, might interact with lymphocyte surface receptor sites and participate in the complex mononuclear phagocyte-lymphocyte interactions and in the modulation of lymphocyte activation.     

Regulation of the human allogeneic proliferative response in vitro

It has previously been shown that presensitized cells in culture medium release suppressor factors (SF) which can inhibit a primary mixed leukocyte reaction (MLA I). This occurs when the presensitized cells are resensitized with an HLA-DR-specific cell, which can be either the primary stimulator or any other DR-identical allogeneic cell. The autologous responders (SF producer cells) and certain allogeneic cells are suppressed, which suggests that restriction takes place. In this paper the effect of preincubation of responder or stimulator cells in SF has been studied: (1) When unprimed responders are preincubated with the suppressor supernates (SF) and tested in MLR I against several stimulators, the cells of the autologous SF producer and certain other allogeneic cells are always inhibited as already observed when SF was added directly to a mixed lymphocyte culture. (2) When the same stimulators are preincubated with the same SF and used as stimulators with the same responders (not preincubated) then inhibition is observed without restriction. This difference in behavior suggests the existence of at least two factors, one acting directly but only on some responders (restricted factor) and the other acting through stimulators on all responders. (3) Filtration of unprimed responders through glass wool (before SF preincubation and coculture with stimulators in MLR I) produces nonadherent T cells which are suppressed more after preincubation with SF than the same cells unfiltrated. This could be due to the existence of a subset of acceptor cells. (4) None of these factors has immunoglobulin characteristics. Their molecular weights are between 40 000 and 70 000 daltons.Abbreviations used in this paper SF suppressor factor - CF control factor - MLR I primary mixed lymphocyte reaction - MHC major histocompatibility complex - MLR II secondary mixed lymphocyte reaction - CML cell-mediated cytotoxicity assay - PHA phytohemagglutinin - ⁵¹Cr chromium 51     

Effect of anti-beta2-microglobulin on antigen and allogeneic lymphocyte-induced proliferation of human lymphocytes.

The effect of anti-beta2-microglobulin (beta2m) on the mixed lymphocyte reaction (MLR), and an antigen-induced proliferative response was studied. Anti-beta2m IgG and Fab' fragments completely inhibited the MLR. Preincubation of stimulator or responder cells with anti-beta2m suggested that the major effect of anti-beta2m may be on the responder cell population. A clear-cut effect on responder cells was demonstrated by showing that anti-beta2m completely inhibited a MLR in which the stimulator population was a beta2m negative lymphoblastoid cell line. Anti-beta2m also inhibited PPD-induced proliferation of sensitized lymphocytes. The kinetics of this inhibition indicated that anti-beta2m added within the first 18 hr of stimulation was effective in inhibiting the proliferative response. These data are discussed in light of the hypothesis that beta2m may be a subunit of an antigen receptor on T cells.     

Progressive loss in vitro immune response with tumor growth.

Peripheral blood lymphocytes from rats carrying a transplantable hepatoma were cultured in the presence of phytohemagglutinin (PHA), concanavalin A (ConA) or dextran sulfate (DS) at various times after tumor cell inoculation or after its surgical removal. Mitogen-induced lymphocyte transformation, measured by tritiated thymidine incorporation, declined as the tumor size increased, especially when cells were cultured in autologous serum. The response to PHA and ConA declined prior to the response to DS. This inhibition could not be removed by extensive washing of the cells, alteration of serum concentration, time of incubation or mitogen dose. Culture for 24 hr prior to the addition of high doses of mitogen resulted in partial restoration of the PHA and ConA, but not DS, responses. Previously inhibited responses also returned when the tumor was surgically removed. Spleen cells from animals with large tumors were also inhibited.     

Measles virus-induced suppression of lymphocyte reactivity in vitro

Measles virus (Edmonston strain B), in various multiplicities of infection, was added to human lymphocytes which were cultured in medium containing fetal bovine serum. Live measles virus was found to cause an almost complete inhibition of [³H]-thymidine incorporation in lymphocytes cultured in the presence of phytohemagglutinin, pokeweed mitogen, tuberculin purified protein derivate (PPD), or allogeneic lymphocytes. Analysis of cell size in the lymphocyte cultures revealed that blast transformation was inhibited as well. Measles virus, inactivated by heat or ultraviolet irradiation, did not cause inhibition. The inhibitory effect of measles virus was only measurable in the initial stages of culture; when added later, i.e., 24 hr before measuring [³H]-thymidine incorporation, it had no effect. The diminished reactivity of measles virus-infected lymphocytes cannot be explained by cytopathologic effects or by altered kinetics of lymphocyte transformation. When lymphocytes were cultured at 39 °C the extent of virus-induced suppression was significantly reduced. Very small amounts of pooled normal human serum, as well as IgG, prepared from the serum of a patient with subacute sclerosing panencephalitis, were able to prevent the inhibitory effect of measles virus.     

The role of protease in streptolysin S formation

Production of streptolysin S by streptococci was found to be inhibited by treatment with protease inhibitors, tosylphenylalanine chloromethyl ketone (TPCK), tosyllysine chloromethyl ketone (TLCK), or phenylmethylsulfonyl fluoride (PMSF), even in the presence of the inducer oligonucleotides. Other protease inhibitors, antipain, leupeptin, or pepstatin were found to have little or no effect. Trypsin reversed the effect of TPCK or TLCK. The reversal was dependent upon the amount of added trypsin and the incubation time at 37 degrees C, suggesting that a protease activity was involved in the hemolysin formation. The effect of trypsin was not observed if chloramphenicol was also added, suggesting that a precursor of streptolysin S was processed as it was synthesized and released into medium as the active hemolysin, by the concerted action of a protease and inducer oligonucleotides. Experiments with the subcellular fractions of streptococci indicated that the streptolysin precursor was localized in the insoluble fraction and the "processing" protease in the supernatant fraction.     

Inhibition of LH-induced and spontaneous meiotic maturation in mouse oocytes by N alpha-tosyl-L-lysine chloromethylketone

The effect of N alpha-tosyl-L-lysine chloromethylketone (TLCK), an inhibitor of trypsin-type proteases, on luteinizing hormone (LH)-induced and spontaneous meiotic maturation and follicular production of cAMP in mice was determined. When follicle-enclosed mouse oocytes were incubated with LH (1 micron/ml), they underwent the breakdown of the germinal vesicle (GVBD). TLCK (0.02-0.5 mM) inhibited LH-induced GVBD in folliculated oocytes. The concentration (0.5 mM) of TLCK that inhibited LH-induced GVBD did not significantly suppress LH-induced cAMP production by follicle cells. The effect of TLCK on spontaneous maturation in cumulus cell-enclosed and denuded oocytes was also determined. TLCK strongly inhibited spontaneous maturation in denuded oocytes only if it was added to the incubation medium for 1-3 h before oocytes were liberated from the follicular tissue. The inhibition of oocyte maturation by TLCK was significantly greater in cumulus cell-enclosed oocytes than in denuded oocytes, either with or without preincubation with TLCK. These results suggest that trypsin-type protease in oocytes participates in the process of meiotic maturation in mouse oocytes.     

Supernatant derived from a human hepatocellular carcinoma cell line (PLC/PRF/5) activates a population of T-suppressor cells

Harvest fluid derived from a primary hepatocellular carcinoma cell line (PLC/PRF/5) inhibited the incorporation of 3H-thymidine into PHA-activated human lymphocytes. A similar effect was observed when lymphocytes were pre-incubated with the tumour supernatant and washed prior to mitogen activation. Not only did the tumour supernatant inhibit 3H-thymidine incorporation by mitogen-activated lymphocytes, but it also inhibited production of the lymphokine leucocyte inhibitory factor (LIF). In experiments designed to establish whether a component of the tumour harvest fluid was activating a population of suppressor cells, normal mononuclear (MN) cells were treated with the PLC/PRF/5 or embryonic fibroblast supernatant for 48 h, after which they were washed and added to normal mitogen-activated lymphocyte cultures. Only cells pretreated with the PLC/PRF/5 supernatant suppressed mitogenesis. The cell responsible for the suppressor effect was a T cell, which after a further 24 h in culture liberated a suppressor factor responsible for inhibiting lymphocyte function. Although the nature of the factor/s in the PLC/PRF/5 supernatant responsible for activation of the T-suppressor cell population is unknown, it is suggested that this mechanism may be important in protecting the tumour from the immune response.     

Reversal of macrophage-augmented MLR reactivity by tumor-induced splenic suppressor T cells and their soluble factor(s)

Augmenting concentrations of macrophages or their supernatants failed to reverse T-cell hyporeactivity in tumor-bearing mice (TBM). Serial passaging over nylon wool columns depleted TBM spleen cells of a mildly adherent tumor-induced suppressor cell and restored mixed lymphocyte reaction (MLR) reactivity to the purified TBM T-cell population. The tumor-induced suppressor cell was extensively plated to remove macrophages and characterized as a T cell by its anti-Thy 1 serum sensitivity. This suppressor T cell, when added to normal T cells, abrogated all enhancing effects caused by addition of macrophages. Suppressor T-cell inhibition was non-contact dependent, since suppressor T-cell supernatants inhibited MLR activity in T cells treated with enhancing concentrations of macrophage supernatants. Thus it appears that tumor-induced T-cell debilitation is a reversible phenomenon, mediated not by macrophages but by soluble factor(s) from a nonphagocytic, mildly adherent, suppressor T cell.