Monocyte function in mixed lymphocyte reactions

Subpopulations of human peripheral blood lymphocytes were isolated by sequential separation techniques. The stimulating and responding capacity of these cells together with the T-cell population remaining after the removal of other populations was studied in one-way allogeneic mixed lymphocyte culture. Incorporation of [³H]thymidine was used as a measure of response. Monocytes, present in the stimulating or responding cell population, were necessary for lymphocyte response. T cells stimulated responding T-cell populations containing monocytes but not B cells. Stimulation by T cells could be inhibited with DRW antisera. Response was also inhibited by sera detecting DRw antigens on the monocytes of the responding cell population. It is concluded that monocytes play an important functional role in mixed lymphocyte reactions. In addition, it appears that the combination of anti-DRw sera and monocytes influences mixed lymphocyte reactions by an active process in that inhibition of response cannot be explained entirely by blocking DRw determinants.     

Detection of HLA-DRw (Ia-like) antigens on human T lymphocytes grown in tissue culture.

Human T lymphocytes that proliferate in the presence of conditioned medium from PHA-stimulated allogeneic peripheral blood cells were shown to express IPA antigens after the 8th culture day. Ia antigens as detected by xenogeneic antisera were present on 80 to 90% of the cultured cells which were also strongly reactive with xenogeneic antisera defining a human T cell antigen and formed E rosettes. Control cultures with PHA or no conditioned medium expressed T cell but not Ia antigens. These cultured T cells also express the same HLA-DRw determinants as the B cells of the donor they were derived from. Absorption of xenogeneic Ia, and HLA-DRw alloantisera with cultured T cells completely removed the reactivity of these sera for enriched peripheral blood B lymphocytes from normal donors.     

Cell-mediated cytotoxicity against HLA-D-region products expressed in monocytes and B lymphocytes. I. Blocking by Unlabelled cells and inhibition by antisera

Cytotoxic effector cells against HLA-D-region produts were generated in cultures with HLA-A- and B-matched, HLA-D-mismatched stimulating cells. Monocytes from unrelated donors sharing HLA-D/DR antigens with the primary stimulator were used as target cells. Lysis of target cells was inhibited by addition of unlabelled monocytes having the same HLA-D/DR antigens. Inhibition of cytotoxicity was also observed with unlabelled B cells, but T lymphocytes had little effect. The distribution of the target antigens, therefore, fits the known distribution of the products of HLA-D. In other experiments, a human alloantiserum specific for HLA-DRw3 was found to inhibit cellular cytotoxicity specific for HLA-D/DRw3. Lysis by HLA-D/DRw3-specific effector cells was not inhibited by sera against HLA-DRw2 or DRw7 or by antibodies against HLA-B8 using HLA-B8 positive, DRw3 positive targer cells. A xenogeneic serum against human Ia antigens, produced in rabbits, blocked cytotoxicity directed at DRw2, DRw3 and DRw4. These results suggest that cell-mediated cyctotoxicity was directed against HLA-D/DR or very closely associated determinants.     

Monoclonal antibodies that inhibit activation and proliferation of lymphocytes. I. Expression of the antigen on monocytes and activated lymphocytes

It has been shown previously that HBJ127 and HBJ98 monoclonal antibodies raised against a human bladder cancer cell line, and B3 monoclonal antibody against a rat bladder cancer cell line recognized unique cell surface antigens abundant in proliferating cells of the corresponding species. Distribution of the antigens and kinetics of the appearance on human and rat lymphoid cells were examined by means of flow cytometry. Rat macrophages and human peripheral blood monocytes were stained strongly with the B3 and HBJ127 monoclonal antibodies, respectively. With regard to lymphocytes, the expression of the B3-defined antigen on rat lymphocytes was found to have a negative correlation with the maturation of the lymphocytes; the antigen was most abundant in bone marrow cells, less abundant in thymocytes, and least abundant in spleen, lymph node, and peripheral blood lymphocytes. Similarly, the HBJ127-defined antigen on human peripheral lymphocytes was negligible. On activation with Con A or alloantigens, however, both rat and human T lymphocytes did strongly express these antigens. Activation of human or rat B cells with lipopolysaccharide also resulted in the augmented expression of these antigens. Kinetics studies revealed that the antigen expression was readily manifested within 12 hr on activation of rat or human T cells with Con A, was augmented progressively with culture time, and reached a plateau within 36 hr. This somewhat earlier appearance of these antigens apparently preceded the manifestations of the IL 2 receptor (Tac antigen) and the augmented DNA synthesis. The B3-defined antigen on Con A-stimulated T cells was more rich on the lymphocytes in S and G2/M phases than those in G1 phase, and the expression was not significantly affected by the addition of hydroxyurea, but was moderately inhibited by the addition of sodium butylate. These results suggest that the appearance and expression of the B3-defined antigen and probably also those of the HBJ127/HBJ98-defined antigen are correlated with lymphocyte activation and subsequent progression through the cell cycle.     

Coexpression of T4 and T8 on peripheral blood T cells demonstrated by two-color fluorescence flow cytometry

Using two-color fluorescence flow cytometry, we were able to detect the presence of small numbers of T4+T8+ cells (about 3%) in freshly isolated peripheral T cell populations derived from normal healthy donors. Coexpression of T4 and T8 was predominantly found on large blastlike cells and appeared to be related to activation. Stimulation of peripheral T cells with concanavalin A (Con A) for 5 days resulted in the generation of up to 60% of T4+T8+ cells. Coexpression was accompanied by a twofold increase in the number of T8 antigenic sites per cell. The T4+T8+ cells in lectin-stimulated cultures expressed high levels of the activation antigens T9, T10, and the IL-2 receptor but lacked T6, an antigen found on a majority of stage II thymocytes. Coexpression of T4 and T8 appeared to be a transitory process, because prolonged culture of T cells in the absence of lectin resulted in the loss of the T4+T8+ phenotype. Our data suggest that T cell activation in peripheral blood results in the generation of a T4+T8+ cell population which is distinct from previously described thymic and peripheral blood cells. Because T4 and T8 molecules may interact directly with MHC antigens, coexpression of these molecules may have an important role in immune function.     

Cell-mediated cytotoxicity against HLA-D-region products expressed in monocytes and B lymphocytes

Cytotoxic effector cells against HLA-D-region products were generated in cultures with HLA-A- and B-matched, HLA-D-mismatched stimulating cells. Monocytes from unrelated donors sharing HLA-D/DR antigens with the primary stimulator were used as target cells. Lysis of target cells was inhibited by addition of unlabelled monocytes having the same HLA-D/DR antigens. Inhibition of cytotoxicity was also observed with unlabelled B cells, but T lymphocytes had little effect. The distribution of the target antigens, therefore, fits the known distribution of the products ofHLA-D. In other experiments, a human alloantiserum specific for HLA-DRw3 was found to inhibit cellular cytotoxicity specific for HLA-D/DRw3. Lysis by HLA-D/DRw3-specific effector cells was not inhibited by sera against HLA-DRw2 or DRw7 or by antibodies against HLA-B8 using HLA-B8 positive, DRw3 positive target cells. A xenogeneic serum against human Ia antigens, produced in rabbits, blocked cytotoxicity directed at DRw2, DRw3 and DRw4. These results suggest that cell-mediated cyctotoxicity was directed against HLA-D/DR or very closely associated determinants.     

In vitro-isolated human cytotoxic T-lymphocyte clones detect variations in serologically defined HLA antigens

T cells of two donors, JR (HLA-A23, 29; B7,7; G; DRw5) and HG (HLA-A2, 23; B40, w44; Cw4), were stimulated with cells from an HLA homozygous lymphoblastoid cell line JY (HLA-A2, 2; B7,7, C-, DRw4, 6) and cloned by limiting dilution after the third stimulation. Two cytotoxic T-cell (CTL) clones, JR-2-16 (from donor JR) and HG-31 (from donor HG), were used for detailed studies. The results of a panel study using lymphocytes from HLA-typed individuals and a study with two HLA recombinant families indicate that the antigens recognized by the CTL clones JR-2-16 and HG-31 were highly associated with HLA-A2 and HLA-B7, respectively. Blocking studies with a monoclonal antibody recognizing a framework determinant on HLA-A, -B and-C antigens and a monoclonal antibody reacting with HLA-A2 support the notion that JR-2-16 and HG-31 interact with the HLA-A2 and the HLA-B7 antigens per se. However, these clones did not recognize the HLA-A2 and HLA-B7 of all donors typed for these antigens, suggesting that the HLA-A2 and HLA-B7 antigens of these particular donors are variants of the serologically defined HLA antigens. These results indicate that in vitro-derived human CTL clones detect variations in the serologically defined allospecificities and can be used as reagents to elucidate the polymorphism of HLA antigens further.Abbreviations used in this paper: CTL cytotoxic - T lymphocytes - BSA bovine serum albumin - PHA phytohemagglutinin - Con A concanavalin A.     

Studies on the mechanism of lymphocyte- mediated cytolysis. VIII. The use of con A to delineate a distinctive killer T cell subpopulation.

Alloimmune spleen cells (C57BL/6 anti P815), but not normal spleen cells, lyse syngeneic (EL4) target cells in the presence of Con A. Con A dependent cytotoxicity was mediated by T cells and required the continued presence of lectin. Cytolysis in the presence of a succinylated derivative was equivalent to that seen with the parent Con A molecule. In contrast to previous reports of Con A dependent cytolysis, however, we conclude that lysis is not primarily caused by directly cytotoxic T cells. The reasons for this conclusion are: 1. Removal of directly cytotoxic cells by adsorption on P815 monolayers did not alter the Con A dependent cytolysis of EL4 cells; 2. Populations in which no direct T killers were demonstrable (e.g., spleen cells harvested 5 days after alloimmunization) lysed both P815 and EL4 cells in the presence of Con A; and 3. Con A dependent cytolysis, but not direct cytotoxicity, could be induced by culturing normal C57BL/6 spleen cells for 4 days with a sonicated extract of P815 cells. We hypothesize that the cell "activated" to lyse targets in the presence of Con A is a T cell which has differentiated lytic potential following alloantigenic stimulation, but has either insufficient density or affinity of antigen receptors to serve as a directly cytotoxic cell. The role of Con A is viewed as 2-fold: i) to "bridge" killer and target cell, and ii) to "activate" the effector.     

Cyclosporin A does not prevent expression of Tac antigen, a probable TCGF receptor molecule, on mitogen-stimulated human T cells

Results of recent studies indicated that a monoclonal anti-Tac antibody might recognize the receptor sites or closely related structures for T cell growth factor (TCGF) on activated human T cells. In the present study, we examined the effect of cyclosporin A (CsA) on the expression of Tac antigen by mitogen-stimulated T cells. CsA inhibited the proliferative response of T cells to Con A and PHA in a dose-dependent manner. Both Con A- and PHA-induced cellular proliferation were decreased to about 10% of controls at 5 micrograms/ml of CsA. When T cells were stimulated with these mitogens, many of them expressed Tac antigen on their surfaces, assessed by the immunoperoxidase method. The appearance of Tac-positive cells occurred earlier than a rise of cellular DNA synthesis. Characteristically, CsA showed no inhibitory effect on the expression of Tac antigen by mitogen-stimulated T cells, even at a relatively high concentration of 5 micrograms/ml, whereas the expression of other "activation" antigens reactive with monoclonal anti-Ia, OKT9, or OKT10 antibodies by T cells was blocked completely by CsA. Morphologically, the majority of Tac-positive cells in culture with mitogens alone showed the characteristics of blastoid cells; Tac-positive cells in the culture containing CsA mainly consisted of medium-sized cells, indicating these cells probably accumulated at a stage of partial activation. T cells, once stimulated with Con A or PHA for 3 days whether in the presence or in the absence of CsA, were able to absorb TCGF activity from TCGF-containing media similarly. In addition, T cells, even stimulated in the presence of CsA with these mitogens for 24 hr, were capable of responding to TCGF with the same grade of proliferation as did T cells stimulated with mitogen alone. CsA showed no appreciable inhibition in a TCGF-dependent proliferation of such prestimulated cells. These functional properties of activated T cells might be correlated with their ability to express Tac antigen. These experimental findings present some evidence that CsA might not prevent the expression of probable functional receptor sites for TCGF in mitogen-dependent activation of human T cells.     

The proliferative response of cloned Peyer's patch switch T cells to syngeneic and allogeneic stimuli

We previously defined a concanavalin A (Con A)-induced cloned T cell population in Peyer's patches (PP) that causes sIgM-bearing B cells to switch to sIgA-bearing B cells. In the present study we show that such IgA-specific switch T cells proliferate when exposed to syngeneic stimulator cells, i.e., the switch T cells are autoreactive. Detailed study of this phenomenon disclosed that both B cells and macrophages were capable of causing switch T cell proliferation, and in both cases, stimulation was enhanced by preactivation of the stimulator cells with lipopolysaccharide (LPS). In addition, fresh T cells can act as stimulators, but only if preactivated with Con A. Finally, it was clearly shown in blocking studies with the use of various antibodies directed at class II MHC specificities that class II MHC antigens were the stimulatory determinants. These studies suggest that IgA-specific switch T cells arise in PP as a result of autologous cell-cell interactions with activated (antigen-stimulated) B cells, macrophages, or T cells.     

Genetic analysis of Ia determinants expressed on Con A-reactive cells.

Pretreatment of mouse lymphoid cells with anti-Ia sera and C abrogated the proliferative responses of these cells to Con A. Studies were carried out with several anti-Ia reagents and intra-H-2 recombinant mouse strains to map the I subregion(s) whose products are expressed on Con A-reactive cells. Treatment with a (B10.A X A)F1 anti-B10 reagent and C abrogated the ability of BALB/c cells to respond to Con A. Absorption studies on this reagent demonstrated that Con A-reactive cells express Ia determinants coded by the I-A subregion. The results with two additional reagents, B10.A(4R) anti-B10.A(2R) tested on B10.BR cells and (B10 X D2.GD)F1 anti-B10.D2 absorbed with B10.A cells and tested on BALB/c cells, demonstrated that Con A-reactive cells also express Ia determinants encoded to the right of I-A. Several antisera and strain combinations were evaluated in which the antisera could contain antibodies specific for products of genes encoded by the I-J subregion, but the results were inconclusive. These data demonstrate that there are at least two different I subregions, one in I-A and one to the right of I-A, that code for antigens expressed on Con A-reactive cells.     

B-Lymphoid cell lines derived fromHLA-D homozygous donors

Multiple lymphoid cell lines were derived from 35HLA-D homozygous donors by EB-viral transformation of B lymphocytes. The expression of Ia-like alloantigens (HLA-DR) was studied by microcytotoxicity and by absorption with alloantisera exchanged through the Seventh Histocompatibility Workshop. B-lymphoid lines expressed the same specificities as normal B lymphocytes. Workshop antisera representing DRw1, DRw2, DRw3, and DRw7 gave well-defined typing patterns with cell lines derived from donors of corresponding D-locus specificities. A more complex reaction pattern was seen for antisera representing DRw4, DRw5, and DRw6. The available reagents could not discriminate between lines from donors homozygous for Dw4, Dw10, or D-KH. All lines studied, except for those from one donor homozygous for a unique D-locus determinant (D-SPO), could be assigned one of the provisional DRw specificities.The advantage of obtaining multiple cell lines from a single donor was evident. One line could not be typed by microcytotoxicity because it was lysed in all human sera tested, and some other lines gave weak cytotoxic reactions. Absorption studies, however, did indicate similar expression of DRw antigens on these lines. The availability of multiple lines from the same donor circumvented these difficulties.     

Alloreactive T cells from individual soft agar colonies specific for guinea pig Ia antigens. II. Cellular and molecular requirements for optimal proliferative responses

We have investigated the cellular and molecular requirement for optimal proliferative responses of several alloreactive T cell lines that were derived from individual soft agar colonies and were specific for guinea pig Ia antigens. Optimal proliferation of several colonies was observed in cultures containing purified allogeneic macrophages and growth factor(s) present in supernatant fluids of Con A-activated T cells (Con A-S). Significant proliferative responses of these alloreactive T cell colonies were also routinely detected in cultures only supplemented with unfractionated irradiated allogeneic peritoneal exudate cell (PEC). The T cell component of the stimulator cell population was crucial for these responses by producing necessary growth factor(s) endogenously in the culture. Thus, 2 signals, allogeneic Ia antigens and growth factor(s), were required for optimal proliferative responses of these alloreactive T cell colonies. Furthermore, macrophage-associated Ia antigen was more efficient than B cell-associated Ia for these responses. The requirement for allogeneic Ia antigen was not absolute, since the colonies could easily be expanded when the cultures were supplemented with irradiated syngeneic PEC and the T cell mitogens, Con A or PHA. The effect of the mitogen was mediated via the T cells in the irradiated PEC, since removal of the T cells from these PEC markedly reduced the responses. Thus, it is likely that a nonspecific signal(s) presumably from T cells can promote proliferation of alloreactive T cell colonies in the absence of allogeneic Ia antigen. These results suggest 2 mechanisms of activation of these alloreactive T cells.     

Antibody-dependent cellular cytotoxicity mediated by murine lymphocytes activated in recombinant interleukin 2

The incubation of murine splenocytes in recombinant interleukin 2 (RIL 2) gives rise to lymphokine-activated killer (LAK) cells that can lyse fresh, NK-resistant tumor cells but not normal cells in 4-hr 51Cr-release assays. Lysis by this IL 2-activated cell population was enhanced up to 100-fold by prior reaction of target cells with specific antisera reactive with antigens on the target cells. This antibody-dependent cellular cytotoxicity (ADCC) also resulted in lysis of fresh normal target cells, which are not usually susceptible to LAK lysis. The ADCC was evident after 24 hr of incubation of splenocytes in RIL 2, but peak lytic activity was reached after 3 to 4 days of incubation. The concentrations of RIL 2 needed for the in vitro activation of the effectors in order to attain maximal ADCC was between 100 and 3000 U/ml and parallel the IL 2 concentrations required to generate LAK cells. ADCC mediated by IL 2-activated splenocytes was completely blocked by anti-FcR monoclonal antibodies. Although antisera directed against MHC antigens were used in most experiments, anti-B16 monoclonal antibodies have also shown the ability to induce ADCC mediated by RIL 2-activated syngeneic and allogeneic cells. Treatment of the precursor splenocyte populations with anti-asialo GM1 and complement eliminated the direct LAK activity and the antibody-dependent cytotoxicity, suggesting that both direct and indirect tumor cell lysis may be caused by the same effector cell. ADCC mediated by LAK cell populations represents another possible mechanism for the in vivo therapeutic effects of these cells.     

Concanavalin A triggers T lymphocytes by directly interacting with their receptors for activation

Anti-HLA-DR antibodies did not inhibit concanavalin A-(Con A) induced T cell proliferation or the generation of suppressor cells capable of inhibiting immunoglobulin synthesis in autologous mononuclear cells after pokeweed mitogen stimulation. Nylon-wool purified T cells (pretreated with anti-HLA-DR antibody and C) exposed to Con A acquired responsiveness to interleukin 2 (IL 2) and were able to absorb this growth factor, whereas nonlectin-treated cells did not respond to IL 2 and could not absorb it. In the presence of interleukin 1 (IL 1), Con A stimulated the synthesis of IL 2 in purified OKT4+ lymphocytes but not OKT8+ cells. However, in the absence of IL 1, neither resting OKT4+ nor Con A-treated OKT4+ cells produced IL 2. Con A by itself did not directly stimulate macrophages to synthesize IL 1, although it could do so in the presence of OKT4+ but not OKT8+ lymphocytes. In addition, Con A induced proliferation of purified T cells provided IL 1 was supplied to the cultures. Cyclosporin A rendered Con A-treated T cells unresponsive to IL 2, made lectin-stimulated OKT4+ lymphocytes unable to respond to IL 1, and inhibited the synthesis of IL 2. Furthermore, this drug abrogated the Con A-stimulated synthesis of IL 1 by acting on OKT4+ lymphocytes and not on macrophages. Finally, cyclosporin-A suppressed the proliferative response and the generation of suppressor T cells induced by Con A. The following are concluded: 1) HLA-DR antigens do not seem to play any role in the triggering of T cells by Con A, and macrophages participate in lectin-induced activation of T cells mainly by providing IL 1. 2) Cyclosporin-A inhibits activation of T cells by interfering with the mechanism by which Con A stimulates T lymphocytes. 3) Con A triggers T lymphocytes by directly interacting with their receptors for activation.     

CD4+CD45RA+ and CD4+CD45RA- T cell subsets in man maintain distinct function and CD45RA expression persists on a subpopulation of CD45RA+ cells after activation with Con A.

We have previously shown that Con A-induced suppressor T cells belong to the CD45RA+ subset. After unseparated T cells are activated with Con A, CD45RA expression increases to a maximum (Day 2), and then decreases significantly, but does not disappear entirely (Day 9), while CD29 expression increases steadily. In the present study, we examined the fate of these cell surface molecules on isolated CD4+CD45RA+ and CD4+CD45RA- cells following activation with Con A, and their relationship to the regulatory functions of these subsets. After activation of CD4+CD45RA+ cells with Con A, CD45RO and CD29 antigen expression rapidly increases (greater than 90%). While CD45RA expression is downregulated, approximately 40% of the cells continue to express low-density CD45RA in a stable fashion through Day 21. Despite these phenotypic changes, cells originally CD45RA+ continue to suppress IgG synthesis and provide only minimal B cell help. Furthermore, when cells originally CD45RA+ were sorted on the basis of continued presence, or loss of CD45RA antigen 14 days after activation, both populations demonstrated potent suppression and minimal help. In contrast, after activation with Con A, CD4+CD45A- cells maintain stable phenotype and provide significant help and minimal suppression. Immunoprecipitation of the CD45RA antigen from Day 14 activated CD4+CD45RA+ cells confirms the continued presence of the 205-kDa isoform, but reveals a significant decrease in the 220-kDa isoform. These results suggest that after activation with Con A, cells originally CD45RA+ remain functionally distinct from cells originally CD45RA-, and that CD45RA antigen persists on a subpopulation of CD45RA+ cells after activation with Con A.     

Requirement for an Ia-bearing accessory cell in Con A-induced T cell proliferation.

Pretreatment of murine lymphoid cells with anti-Ia and C abrogated the proliferative response of these cells to Con A, but not to PHA. Reconstitution experiments demonstrated that T cell-enriched populations failed to restore Con A responsiveness and that T cell-depleted populations were more effective in restoring responsiveness to Con A. In particular, a population of 1000 R resistant, glass-adherent, non-T spleen cells was capable of completely restoring responsiveness to Con A when added in numbers as low as 4% of cultured cells. These splenic adherent cells were found to express Ia determinants encoded by at least two genes: one in I-A and the other in I-B, I-J, and/or I-E/C, and it was demonstrated that determinants encoded in these two regions were expressed on the same cell. These results demonstrate that non-T accessory cells may be the Ia+ cells entirely responsible for the anti-Ia and C-induced abrogation of T cell proliferative responses to Con A.     

Mitogenic Activity of a Water-Soluble Adjuvant (Bu-WSA) Obtained from Bacterionema matruchotii

Butanol-extracted water-soluble adjuvant (Bu-WSA) obtained from Bacterionema matruchotii was cultured with peripheral blood mononuclear cells (PBM) in the presence of sub- and/or supra-optimal mitogenic concentrations of concanavalin A (Con A). The addition of Bu-WSA resulted in increased tritiated thymidine incorporation above that produced by Con A alone. Bu-WSA by itself is not mitogenic for PBM and in fact produced a decrease in thymidine uptake compared to the control. We investigated the response of subpopulation(s) of PBM to Bu-WSA, Con A and a mixture of Bu-WSA and Con A. Separation of PBM into purified T cells, B cells and macrophages showed that cell-cell cooperation of T cells with B cells or macrophages is necessary for the observed synergistic effect of Bu-WSA with Con A. A marked increase in thymidine incorporation by the mixture of T and B cell populations occurred, while only a small amount of thymidine was incorporated when the B cell population was absent. Mitomycin treatment revealed that the response could be ascribed to the T-cell response with a B-cell helper effect. Moreover, Con A and Bu-WSA appeared to act on the same T cell population. This model may provide unique information about the activation of human peripheral blood T cells compared with the activation of these cells by other mitogens.     

Characterization of lymphocyte responsiveness in early experimental syphilis. I. In vitro response to mitogens and Treponema pallidum antigens

Lymphoid cells from spleens and lymph nodes of rabbits infected with T. pallidum respond by proliferation to concanavalin A (Con A) and T. pallidum antigens. Spleen cell responsiveness to treponemal antigens appears 6 days after infection, is 100 to 600 fold higher than the response of uninfected control rabbits, and is maintained throughout the 31-day observation period. Specifically responding cells in the inguinal and popliteal lymph nodes of infected animals are demonstrable on day 10, and the magnitude of the response increases throughout the observation period. Specific responsiveness to T. pallidum antigens in vitro is enhanced in purified T cell populations and is abolished by treatment with goat anti-rabbit thymocyte serum and complement. The response of spleen and lymph node cells to Con A is unaffected during syphilitic infection. These results are consistent with a role for T cell-mediated specific immunity to treponemal antigens early after infection and do not support a hypothesis of depressed cellular immunity during syphilitic infection.     

Inhibition of modulation of thymus-leukemia antigens by concanavalin A.

When incubated at 37 °C in medium containing antibodies specific for thymus-leukemia (TL) antigens, viable cells bearing these antigens become resistant to the cytolytic effects of guinea pig complement, a process termed antigenic modulation. Antibody-induced membrane redistribution of the TL antigens, detected by indirect immunofluorescence, occurs with a similar pace. When high concentrations of concanavalin A (Con A) were included with antibodies in the incubation medium, TL antigenic modulation as well as antigen patching and capping were markedly inhibited, similar to effects of Con A on membrane immunoglobulin redistribution with murine spleen cells. Colchicine antagonized the inhibition by Con A suggesting the involvement of microtubules. In parallel experiments high concentrations of Con A failed to alter the quantity of TL antigen expression or its rate of change with time during incubation in cognate antisera. These results support the hypotheses that (a) generalized alterations in membrane receptor mobility may be induced by ligand binding to the cell membrane, and (b) under certain conditions stable interactions occur between normally independent cell surface antigens.