Veto cell H-2 antigens: veto cell activity is restricted by determinants encoded by K, D, and I MHC regions

Responder cells from primary syngeneic and allogeneic one-way mixed-lymphocyte cultures (MLC) specifically inhibit the development of cytotoxic T lymphocytes (CTL) directed against the major histocompatibility complex (MHC) antigens of the MLC responder cells. This special kind of suppressor activity is known as veto suppression. Ia+ cells with veto activity obtained from H-2 recombinant mouse strains were shown to downregulate alloantigen (class II)-specific helper activity for class I-specific CTL development in a primary MLC provided that the veto cells expressed the same I-E alpha subregion as the MLC stimulator cells. The veto-induced suppression of allo-help was prevented by the addition of supernatant from concanavalin A-stimulated spleen cells (Con A-SN) and was inhibited considerably by very high amounts of recombinant interleukin-2 (IL-2). In the presence of Con A-SN, CTL precursors recognizing either the K end or the D end of the veto cell MHC were found to be inactivated. Thus, our results indicate that MLC responder cells include active veto cells expressing Ia region-encoded restriction elements for allospecific T helper cells, as well as K- or D-encoded restriction elements for allospecific T cytotoxic cells.     

Induction and characterization of minor histocompatibility antigens. Specific primary cytotoxic T lymphocyte responses in vitro

A definite cytotoxic activity was developed in a BALB/c (H-2d) anti-DBA/2 primary mixed leukocyte culture (MLC), which received interleukin 2 (IL-2) on day 3 of culture. This cytotoxic activity was minor histocompatibility antigens (MIHA)-specific at the stimulator level, and was not developed in a syngeneic (BALB/c anti-BALB/c) MLC. The addition of IL-2 on day 3 of culture was crucial; no or very weak cytotoxic activity was developed in MLC receiving IL-2 on day 0 or on both day 0 and day 3. Only appropriate MIHA-allogeneic tumor cells were lysed as the target of the cytotoxic activity. The cytotoxic activity seemed MIHA-specific also at the target level; it lysed tumor cells of DBA/2 mouse origin but not those of BALB/c (syngeneic) origin. Phenotypes of the cytotoxic effector cell were Thy-1+ Lyt-2+. We concluded from these results that MIHA-specific cytotoxic T lymphocytes (CTL) were generated in the MIHA-allogeneic primary MLC. In this newly developed system, we studied genetic and antigenic requirements for primary anti-MIHA CTL responses in vitro. We demonstrated; among spleen cells (SC) of seven B10 H-2-congenic strains only SC of B10.D2 strain whose major histocompatibility complex (MHC) (H-2d) was compatible with the responder MHC effectively stimulated responder BALB/c (H-2d) SC for an anti-MIHA (DBA-C57BL-common) CTL response. Similarly, only SC of two out of seven C x B recombinant inbred strains (C x B.H and C x B.D), which were compatible at the MHC with responder SC, activated responder BALB/c SC for the response. The possibility that cells responding to H-2 alloantigens suppressed the anti-MIHA response was ruled out. Additional experiments showed that compatibility at the H-2K-end or the H-2D-end of the MHC was sufficient for a definite anti-MIHA response. These provided formal evidence that primary anti-MIHA CTL responses in vitro were MHC-restricted at the stimulator level. We then showed that sonication-disrupted SC or Sephadex G-10 column-passed nonadherent SC failed to stimulate responder SC for a primary anti-MIHA CTL response, whereas G-10-passed nonadherent SC responded well to adherent stimulator cells. Further study demonstrated that Ia+ adherent cells were the most active cell type as stimulator. Finally, we confirmed that the primary anti-MIHA CTL responses to adherent stimulator cells was MHC-restricted.     

Lymphocyte responses to syngeneic antigens. I. Enhancement of the murine autologous mixed lymphocyte response by polyethylene glycol

The normally weak murine T-cell proliferative response against autologous non-T stimulator cells (the autologous mixed lymphocyte culture (MLC) was enhanced markedly by inclusion of the hydrophilic polymer, polyethylene glycol (PEG), into the culture medium. Potentiation of the autologous MLC was indicated on the basis of increased [³H]TdR incorporation by responding cells, as well as by the numbers of viable cells recovered from mixed cell cultures. PEG is not a polyclonal activator of T and/or B lymphocytes, since nylon wool nonadherent lymphoid cells (T cell-enriched fraction), nylon wool adherent cells (B cell-enriched fraction) and T cell-deficient “nude” spleen cells were not stimulated into DNA synthesis when cultured separately with PEG. Inclusion of 4% PEG into the culture medium was found to optimally enhance autologous MLC, although concentrations between 2 and 5% also significantly elevated responsiveness. At a responder/stimulator ratio of 1:2, autologous MLC yielded peak [³H]TdR incorporation after 5 days of culture. At lower ratios (1:1 and 2:1), however, Δ cpm of autologous MLC continued to increase over a culture period of 7 days. Enhanced responsiveness in the presence of PEG was observed in strains of mice representing a variety of H-2 haplotypes, indicating that at least the potential for autoreactivity of this type is a naturally occurring and widespread characteristic of murine species. An absolute requirement for purified T responder cells was necessary in the autologous MLC, since unseparated lymphoid cell responder LN or spleen cells demonstrated marked proliferation when cultured alone in medium containing PEG. The proliferation of T cells to autologous non-T cells within the same unseparated lymphoid cell preparation appears to be responsible for this phenomenon. Ia antigens expressed by the stimulator cells are involved in the induction of T-cell response, since anti-Ia sera added directly to the cultures inhibited the autologous MLC, but did not affect other T-cell responses to alloantigens or mitogens. Despite the marked proliferation observed in the autologous MLC performed in the presence of PEG, there was no generation of cytotoxic effector cells. Thus, PEG does not appear to add, or alter determinants on stimulator cells to an extent that they are recognized as foreign by precursor cytotoxic T cells. Although the mechanism of enhancement of autologous MLC by PEG is not totally defined, it appears, at least functionally, to promote cellular interactions that occur normally between T cells, B cells, and macrophages. In this respect, PEG will be a powerful and useful probe to dissect the cellular interactions that take place in autologous responses.     

H-2K/H-2D and Mls and I region-associated antigens stimulate helper factor(s) involved in the generation of cytotoxic T lymphocytes

This study examines the antigen that stimulate production or release of a soluble helper factor(s) involved in development of cytotoxic T lymphocytes (CTL). Antigens associated with the Mls locus, I and K/D regions of the MHC were all capable of stimulating responder cells in MLC to produce helper factor. These supernatant fluids were all capable of providing "help" for the generation of cytotoxic T lymphocytes in MLC in which spleen cells are stimulated by allogeneic heat-treated thymocytes or splenocytes. Previous reports from our laboratory as well as others have shown that heat-treated cells do not stimulate a cytotoxic response. Heat-treatment of Mls, I, and H-2K/H-2D region incompatible stimulatory cells in MLC eliminated their ability to induce responder cells to produce helper factor, suggesting this is the mechanism whereby heat-treatment reduces the ability of cells to stimulate cell-mediated lympholysis (CML). The inability of supernatant fluids, from MLCs in which heat-treated cells were the stimulators, to assist in the generation of cytotoxic T cells did not appear to be the result of any suppressive factor induced by such treatment. Further, the antigens that stimulate pre-killer cells appear functionally distinct from those heat labile antigens (Mls, I, H-2K/H-2D associated) that stimulate helper factor production since heat-treated allogeneic cells served as stimulators of cytotoxicity provided helper activity was added to the MLC.     

Inhibition of stimulation in murine mixed lymphocyte cultures with an alloantiserum directed against a shared Ia determinant.

Pools of high titered alloantisera were raised by immunizing (B10.A/SgSn X A/WySn)F1 mice with C57BL/10Sn(B10) spleen cells. This serum (F1 anti-B10), when added to one-way mixed lymphocyte cultures (MLC), inhibited stimulation of B10.A splenic responders by both B10 and B10.D2/nSn irradiated, splenic stimulators. The B10 stimulation was suppressed approximately 85% whereas the mean suppression of B10.D2 stimulation was approximately 60%. In the ofrmer case, the serum contained antibodies reactive with multiple major histocompatibility complex determinants on the stimulator cells. In the latter case, the cytoxic reactivity of the serum was directed principally against an I region-associated determinant Ia.8) shared by B10 and B10.D2 and coded for by a gene(s) in the I-A subregion. The magnitude of the suppression of the response to B10.D2 cells (60%) was similar to the reduction in stimulation observed when the Ia.8 difference was eliminated genetically by using (B10 X B10.A)F1 responder cells against irradiated B10.D2 stimulators. Ihhibition of MLC by this antiserum was a function of reactivity with stimulator and not responder cells. Although some pools of F1 anti-B10 antiserum produced partial inhibition of the responder cell in a B10.D2 vs B10.Ax MLC combination, the results were inconsistent and not correlated with the anti-Ia.8 cytotoxicity titers. In addition, an F1 anti-B10 antiserum pool, which consistently failed to inhibit the responder cell, nevertheless inhibited both irradiated B10.D2 and (B10.A X B10.D2)F1 cells from stimulating B10.A responder cells. However, this same antiserum did not inhibit stimulation of B10.D2 responder cells by the (B10.A X B10.D2)F1 stimulators. Thus, the binding of antibodies to the non-stimulating antigens on the F1 stimulator cell did not interfere with the capacity of the appropriate stimulating antigens to cause stimulation. All of these results are consistent with the hypothesis that Ia allo-antigens are the major stimulating determinants of I region-associated MLC reactions.     

Nature of the antigenic complex recognized by T lymphocytes. IV. Inhibition of antigen-specific T cell proliferation by antibodies to stimulator macrophage Ia antigens.

We have previously demonstrated that nonimmune guinea pig T lymphocytes could be specifically sensitized with TNP-modified allogeneic macrophages after eliminating the alloreactive T cells with bromodeoxyuridine (BUdR) and light treatment. This procedure allowed the unique opportunity to use anti-Ia sera directed against the Ia antigens of only the stimulator macrophages or responder T cells to determine against which cell type anti-Ia would block TNP-specific stimulation. It was found that the TNP-specific DNA synthetic response of BUdR and light-treated T cells stimulated with TNP-modified allogeneic macrophages was totally eliminated by anti-Ia sera directed solely against the allogeneic stimulator macrophage. In contrast, anti-Ia sera directed only against the responder T cells had no effect on their response to TNP-modified allogeneic macrophages. These findings indicate that macrophage Ia antigens are required for efficient T cell-macrophage interactions and raise the possibility that T cell Ia antigens may not be required for collaboration with macrophages. This latter possibility was substantiated by experiments in which we show that treating T cells with anti-Ia sera and complement to remove the Ia-positive cells either before or after priming, or both, had no effect on their ability to be primed and restimulated with TNP-modified macrophages.     

Regulation of the in vitro presentation of minor lymphocyte stimulating determinants by major histocompatibility complex-encoded immune response genes

Activation of murine B lymphocytes in a splenocyte stimulator population with affinity-purified goat anti-mouse IgD (G alpha M delta) antibody was previously shown by this laboratory to enhance the presentation of strongly stimulatory major histocompatibility complex (MHC) and minor lymphocyte-stimulating (Mlsa,d) determinants in a primary mixed lymphocyte reaction. In the present study, the G alpha M delta treatment of murine splenocytes was employed to enhance the detection of the weakly stimulatory non-MHC Mlsc determinant in order to study the role the MHC might play as a restricting element for the recognition of these minor antigens in a primary mixed lymphocyte reaction. Indeed, enhanced T cell proliferation to Mlsc determinants presented on G alpha M delta-treated splenocytes was observed when the responder and activated H-2-compatible stimulator cell shared certain MHC haplotypes. High responsiveness was associated with the H-2a,k,j,p haplotypes, intermediate responsiveness was associated with the H-2f,g haplotypes and low responsiveness was associated with the H-2b,s haplotypes. (Low X high responder)F1 T cells preferentially responded to the Mlsc determinants presented on G alpha M delta-treated stimulator cells of the F1 or parental high responder H-2 haplotype. When mitomycin C instead of irradiation was used to inactivate normal (non-IgD-treated) splenocytes, a similar preferential response of T cells to Mlsc determinants presented on stimulator cells of a high responder H-2 haplotype was also observed. The inability of G alpha M delta-treated splenocytes of the low responder haplotype to elicit substantial levels of T cell proliferation across an Mlsc difference could not be attributed to the failure of these stimulator cells to become activated by the anti-Ig antibody. In addition, co-culture experiments could not identify the poor T cell response to Mlsc determinants presented on certain MHC haplotypes as being caused by the induction of nonspecific suppressor cells. Presentation of Mlsc determinants caused by transgene product complementation was detectable in F1 mice derived by crossing one parent that had the Mlsc non-MHC genes and a poorly permissive H-2 haplotype with a parent that expressed a permissive H-2 haplotype but lacked the Mlsc non-MHC genes.(ABSTRACT TRUNCATED AT 400 WORDS)     

Stimulator cell requirements for allospecific T cell subsets: specialized accessory cells are required to activate helper but not cytolytic T lymphocyte precursors

Murine cortisone-resistant thymocytes were separated by staining with monoclonal anti-Lyt-2 antibody and FMF into Lyt-2- and Lyt-2+ subsets in order to analyze the nature of stimulator accessory cells required to activate each of these functionally distinct T cell subpopulations. The Lyt-2- fraction was able to proliferate but not to generate cytotoxic cells when stimulated by irradiated allogeneic spleen cells. Fractionation of the stimulator population showed that low numbers of dendritic cells and splenic macrophages, but not equivalent numbers of whole spleen cells or peritoneal macrophages, were able to stimulate the Lyt-2- population. On the other hand, the Lyt-2+ population, which showed little if any proliferation in response to irradiated spleen cells, contained all the precursors of cytolytic T lymphocytes. In contrast to the highly specific stimulator requirement of the Lyt-2- fraction, allospecific cytotoxic cells were generated from Lyt-2+ cells by any alloantigen-bearing stimulator cell provided interleukin 2 was present. This was confirmed by limiting dilution analysis: alloreactive CTL-P frequencies in spleen and thymus were not influenced by the nature of the stimulator cell. These data collectively indicate that heterogeneous Ia+ accessory cells are required to stimulate helper but not cytolytic T cell precursors.     

Prethymic nylon wool-passed bone marrow cells, substituting for helper T cells, can augment the generation of cytotoxic T lymphocytes from their precursors.

Nylon wool-passed bone marrow (NW-BM) cells treated with anti-Thy.1 monoclonal antibody and complement were added to a mixed lymphocyte culture which contained a limiting number of lymph node cells, as responder cells, and a sufficient number of mitomycin-c-treated allogeneic spleen cells as stimulator cells. NW-BM cells of the same MHC haplotype as responder cells enhanced the generation of allo-specific cytotoxic T lymphocytes (CTL) not only at a relatively high dose (3 x 10(3) cells/well) of responder cells, but also at an extremely dilute dose (1 x 10(3) cells/well). NW-BM cells which had a third-party MHC haplotype, a haplotype different from both responder and stimulator cells, also enhanced the generation of CTL at relatively high doses, but not at low doses, of responder cells. NW-BM cells which had MHC haplotypes identical with those of responder cells induced CTL from helper T cell-depleted responder cells, but NW-BM cells which had the third-party haplotype did not. These results showed that the enhancing effects of NW-BM cells of the same MHC haplotype as responder cells might be due to a specific helper effect and the enhancing effect of NW-BM cells of the third-party haplotype might be due to a nonspecific filler effect, which only conditioned the cultured cells. It was also found that, to exhibit the helper effect, NW-BM cells had to possess MHC class II, but not MHC class I, molecules in common with CTL precursors. This study showed that in the induction of CTL, prethymic NW-BM cells had a capability comparable to that of mature helper T cells.     

Cell types involved in cytotoxicity induced by heated cells and inhibition of this cytotoxicity by anti-human B cell sera.

We have studied the induction of cytotoxic activity in human peripheral blood lymphocytes by heated allogeneic cells. By separating T and B cells from the responder and stimulator cell populations we found that cytotoxic cells are generated in responder T cell populations by both T and the B stimulator cells. Rabbit antisera to a membrane glycoprotein complex (33,000 and 27,000 m.w. by SDS-gel electrophoresis) isolated from a human B cell line were utilized to explore further the nature of the effector cells in this type of cytotoxicity. This antiserum, present during the 6-day-culture period, blocked generation of cytotoxic effector cells. Depletion of cells bearing the B cell antigen from the responder cell population by anti-B cell serum and complement (C) eliminated cytotoxicity. Furthermore, heated cell-induced cytotoxicity was blocked by simply pretreating the responder or the stimulator cell populations with anti-B cell serum in the absence of C. Apparently the human lymphocyte that functions as the effector cell in heated cell-induced cytotoxicity bears the Ia-like antigen that might be important in triggering this type of cytotoxicity.     

A permanent human cytotoxic T-cell line with high killing capacity against a lymphoblastoid B-cell line shows preference for HLA A,B target antigens and lacks spontaneous cytotoxic activity

The optimal conditions for the generation of highly cytotoxic human T lymphocytes (CTL) in vitro against a lymphoblastoid B-cell line (JY) in primary and secondary mixed lymphocyte cultures (MLC) were investigated. Variation of the stimulator:responder (S:R) cell ratio influenced both the specific cytotoxicity and the spontaneous cytotoxicity as well as the recovery of the responder cells. T lymphocytes of donor JR (HLA A23,29; B7,7; DRw5) were stimulated with JY (HLA A2,2; B7,7; DRw4,6) in primary and secondary MLC at S:R ratios of 1:50 and 1:10, respectively, since stimulations at these S:R ratios resulted in the highest specific cytotoxicity against JY, the lowest spontaneous cytotoxicity against K562 and Daudi, and in a good recovery of the responder cells. From these T-lymphocyte cultures an exponentially growing CTL line (JR-2) was obtained by weekly stimulations with irradiated JY cells at a S:R ratio of 1:1. After 2 months of culturing the growth rate of the JR-2 cells declined, but could be restored by the addition of conditioned medium, containing T-cell growth factor (TCGF). Irradiated JY cells or TCGF alone were insufficient to maintain proliferation. JR-2 cells were strongly cytotoxic for JY (50% lysis was obtained at an effector:target ratio of 1:2) but the cytotoxic activity against a classical target cell for spontaneous cytotoxicity (K562) was negligible. The cytotoxic activity of JR-2 cells against JY could be inhibited by a monoclonal antiserum W6/32, which recognizes all HLA A, B, and C specificities, and by a monoclonal antiserum directed against β2 microglobulin, whereas monoclonal anti-Ia antisera showed no inhibition. JR-2 cells lysed fresh HLA A2-homozygous lymphocytes more efficiently than HLA A2-heterozygous lymphocytes, whereas the latter were better killed than HLA A2-negative lymphocytes.     

The necessity for T cell help for human tonsil B cell responses to pokeweed mitogens: induction of DNA synthesis, immunoglobulin, and specific antibody production with a T cell helper factor produced with pokeweed mitogen.

Human B lymphocytes obtained from tonsils do not proliferate when stimulated with pokeweed mitogen. A soluble factor produced from T cells cultured with pokeweed mitogen stimulates B cells to synthesize DNA and differentiate into immunoglobulin producing cells. This PWM produced supernatant induced a PFC response to SRBC. The T cell supernatant activity is produced within 12 hr of stimulation in the presence of serum and without a requirement for T cell division. Optimal stimulation of B cells occurred at 7 to 9 days of culture. This helper factor activity eluted postalbumin from a column of Sephadex G-200. Insolubilized pokeweed mitogen was not mitogenic for B cells. The continuous presence of the lectin in culture was not required for B cell proliferation or for immunoglobulin synthesis.     

Functional significance of the Fc receptor on mixed lymphocyte culture-activated T blasts.

Fc receptor (FcR)-carrying blast cells were separated from nonFcR blast cells after priming in primary mixed lymphocyte culture (MLC) by erythrocyte-antibody rosetting and by 1-g velocity sedimentation. Both types of blast cells were cytotoxic to relevant allogeneic target cells in vitro. The FcR-positive and FcR-negative blasts were then plated on a feeder layer syngeneic to the primary MLC responder cells. After feeder layer culture both types of cells reverted into secondary small lymphocytes. When restimulated with the original stimulator cells, both types of secondary lymphocytes produced the relevant secondary cell-mediated lysis responses. Thus no functionally dissimilar subclasses of secondary T lymphocytes can be distinguished in the MLC-stimulated T-cell population on the basis of the FcR.     

Differentiation of NK-like cells from OKT3-, OKT11+, and OKM1+ small resting lymphocytes by culture with autologous T cell blasts and lymphokine

NK-like cells have been generated in vitro from a resting lymphocyte population of PBMC by 8 days culture with mitomycin C-treated autologous T cell blasts and lymphokine. The responder lymphocyte population was purified to the extent that it lacked classical NK cells, and lacked the precursors of MLC-derived NK-like cells and of lymphokine-activated killer cells. The NK-like cells were not generated when the responder lymphocytes were cultured with either T cell blasts or lymphokine alone. Thus, at least two signals are required for their activation. Metabolically inactive T cell blasts plus lymphokine were effective in stimulating the generation of NK-like cells, suggesting that a membrane determinant on the T cell blasts was involved in activation. The phenotype of the NK-like cells and their precursors was analyzed by monoclonal antibody and complement treatment. The phenotype of both precursor and effector cells was OKT3-, OKT11+, and OKM1+, with a distinct pattern of reactivity with OKT8 and Leu-7 for each individual donor tested. The NK-like cells were morphologically large granular lymphocytes, and they killed a variety of target cells. These studies show that signals provided by autologous T cell blasts and lymphokine are essential in triggering the differentiation of NK-like cells from appropriately purified resting lymphocytes. This mechanism of activation could occur in vivo, leading to the generation of NK cells subsequent to an antigen-specific T cell response.     

In vitro analysis of allogeneic lymphocyte interaction. IV. Dual recognition of B cell-associated Mls locus and I-region determinants by a helper allogeneic effect factor (AEF) generated across a minor H locus disparity.

A helper allogeneic effect factor (AEF) was produced across an incompatibility at the minor histocompatibility loci. This AEF is genetically restricted in its activity since it helps B cells only of the stimulator haplotype and of haplotypes that share both an Mls and I-region identity with the stimulator haplotype. The I-region genes involved here map to the I-A and/or I-C subregions. An anti-LyM immunoadsorbent column but neither an anti-H-2 nor an anti-Ia column absorbed AEF helper activity. It is suggested that the activation of T helper cells by a positive allogeneic effect across a minor H locus difference and their genetically restricted interaction with allogeneic B cells may in part be due to the acquisition by alloactivated T cells of stimulator cell-derived LyM and/or Mls determinants. The data presented indicate that helper T cells recognize Mls locus alloantigens in the milieu of self Ia antigens.     

Immune response to the p-azobenzenearsonate (ABA)-GAT conjugate. II. Hapten-specific T cells induced with ABA-GAT in GAT responder X nonresponder F1 hybrids are restricted to the nonresponder haplotype

Immunization of mice with the ABA-GAT conjugate stimulates GAT-specific T helper cells in GAT-responder animals and ABA-specific helpers in nonresponders. Unexpectedly, immunization of (responder X nonresponder) F1 mice, which have the GAT-responder phenotype, leads to the recruitment of both ABA- and GAT-specific clones of T helper lymphocytes. The GAT-reactive population is restricted to the haplotype of the responder parent (Iak), whereas ABA-specific T cells are mostly restricted to the nonresponder one (Ias). This is demonstrated by the ability of monoclonal antibodies to parental la antigens to inhibit T cell proliferation to GAT or ABA-Tyr in vitro. Consistently, ABA-GAT-primed F1 T cells can only activate nonresponder B cells to proliferate in the presence of ABA-Tyr and responder B lymphocytes in the presence of GAT. Furthermore, F1 T cells seem to recognize both ABA and GAT epitopes only in association with molecules encoded by the I-A subregion. Analysis of ABA-specific F1 T cell lines generated by in vitro stimulation with ABA-Tyr or ABA-GAT demonstrates a competition between GAT- and ABA-specific T cells present in the hybrid T cell repertoire and restricted to the same parental I-Ak molecule. The results indicate that F1 macrophages can present both ABA and GAT epitopes to T cells in association with the two parental and hybrid Ia determinants. It seems unlikely that the absence of GAT-specific T cells restricted to the nonresponder I-A in the F1 is due to suppressor T cells. Thus, the competition model that we propose, to explain the selective F1 T cell response to ABA-GAT, leads us to believe that GAT nonresponder animals may lack clones capable of recognizing, with a high affinity, I-As + GAT.     

Regulation of the cytotoxic activity of alloreactive cytotoxic T lymphocytes by helper cells and lymphokines

The cytotoxic activity of alloreactive cytotoxic T lymphocytes (CTL) was maintained and augmented by transferring cells from a 5-day mixed lymphocyte culture MLC into a host culture (HC) containing indomethacin, freshly explanted normal spleen cells, and peritoneal cells which were syngeneic to the MLC cells. The MLC cells used in the transfer experiments were generated by culturing untreated H-2b splenic responders with irradiated H-2d stimulators, or were generated by culturing Lyt-2-depleted H-2b splenic responders with irradiated H-2d stimulators. The allo-CTL were found to be derived from the donor MLC (first culture) when unfractionated MLC cells were transferred into a host (second) culture and incubated for 5 days. In contrast, the allo-CTL were derived from host culture cells when Lyt-2-depleted MLC cells were transferred and the combined cultures incubated for 5 days. In the former case, the augmentation of MLC-derived cytotoxicity did not result from nonspecific expansion of all donor T cells; instead it was mediated by lymphokine(s), distinct from IL-2, produced by helper T cells generated in host culture, which appeared to selectively expand the antigen-specific CTL or to increase the cytotoxic activity of these CTL. The helper T cells were Thy-1+, L3T4+, and Lyt-2-. These findings indicate that antigen-nonspecific help was provided by helper cells or helper factors (lymphokines) generated in the host culture, which maintained and augmented the cytotoxic activity of the fully generated allo-CTL. This helper effect was also seen in the induction of primary allo-CTL responses which could be generated with fewer stimulating cells and with a stronger cytotoxic response at different R/S ratios tested. The generation of allo-CTL in second culture following transfer of Lyt-2-depleted MLC cells to host cultures appears to have involved antigen carryover from the MLC; however, antigen carryover alone was not sufficient. It appears that in the absence of Lyt-2+ suppressor T cells, antigen-specific help might be generated in donor cultures (Lyt-2-depleted MLC) which promoted or recruited the generation of antigen-specific CTL in host culture.     

Characterization of a serum inhibitor of MLC reactions. III. Specificity: HL-A-related antibodies.

A mixed leukocyte culture (MLC)-inhibitory serum from a healthy multipara, JH, has been characterized with regard to the specificity of its inhibitory antibody. When added directly to MLC, JH serum will inhibit most combinations. However, when lymphocytes intended as responder or stimulator cells in MLC were preincubated with this serum, the specificity narrowed considerably. Four groups of lymphocyte donors were recognized, depending upon whether their lymphocytes were inhibited as responders, as stimulators, as both, or as neither. Absorptions of inhibitory activity, followed by assay of the absorbed sera in pretested MLC combinations, yielded reliable data for determining which donors' cells shared pertinent antigens. An association of MLC inhibition by JH serum with the HL-A types of the involved lymphocytes was observed and these relationships are summarized in Table 4. The three HL-A specificities identified, W19, W29, and 12, correspond with the HL-A typing of the husband of the serum donor. Various cell types absorbed relevant inhibitory activity (against responder and stimulator functions) in the following order of efficiency: LCL cells, B lymphocytes, T lymphocytes, fibroblasts, and erythrocytes. When the above three HL-A specificities were removed by absorption, the serum was no longer inhibitory in any combinations. Whether the inhibitory activity of JH serum is directly related to anti-HL-A antibodies or to antibodies against closely related MLR determinants will depend to a large extent upon the degree of linkage disequilibria found between W19, W29, and 12 antigens and the MLR locus.     

Lipopolysaccharide-induced immunomodulation of the generation of cell-mediated cytotoxicity. I. Suppression of the development of cytotoxic lymphocytes

Bacterial lipopolysaccharide from a variety of Gram-negative organisms suppresses the development of cytotoxic killer cells in the murine MLC. Cytotoxic T lymphocytes were generated in vitro by incubating BALB/c responder spleen cells with irradiated C57BL/6 stimulator cells for 5 days in mixed lymphocyte culture (MLC). The addition of LPS at the initiation of MLC suppressed killing of 51Cr-labeled target cells in a dose-dependent manner. LPS was active only during the afferent phase of CMC, since it did not interfere with the efferent phase of the assay. Furthermore, timed addition and timed removal studies suggested that the presence of LPS during the first 48 hr of MLC was critical for maximal suppression of CMC. Lipid A extracted from LPS, which had been shown to be highly suppressive when added to the sensitization phase of the CMC assay, was also inhibitory. Moreover, when LPS was added to MLC in the presence of tritiated thymidine, the proliferative activity of the responder cells increased markedly after 72 hr of culture. These data suggest that LPS, a known B cell mitogen, can modulate the complex sequence of cellular interactions that leads to the generation of cell-mediated cytotoxicity.     

In vitro immunization. Effect of growth and differentiation factors on antigen-specific B cell activation and production of monoclonal antibodies to autologous antigens and weak immunogens

The antigen-specific activation of murine nonimmunized B lymphocytes subsequently used in hybridization experiments has been investigated by using phylogenetically conserved antigens or autologous immunogens. This in vitro immunization was supported by B cell growth and differentiation factors derived from phorbol myristate acetate-stimulated EL-4 thymoma cells and mixed lymphocyte cultures (MLC). A filter immuno-plaque assay was used to evaluate the effect of different activation procedures on the number of antigen-specific plaque-forming cells (PFC). We first determined the requirement for MLC-derived lymphokines in the in vitro immunization. An optimal number of antigen-specific PFC was obtained when using 33 to 50% of the supernatant from a 48-hr MLC to support the activation. B cell growth and differentiation factors derived from EL-4 cultures were then tested for their abilities to potentiate the number of PFC by using both unseparated spleen cells and highly purified Ig-positive B cells as target cells. The combination of lymphokines found in supernatants from 25% EL-4 thymoma culture and 33% MLC yielded the highest number of PFC when used to support an in vitro immunization. This optimal factor preparation was used to determine the kinetics (4 to 7 days) and the dose response (0.01 to 10 micrograms antigen/ml) of antigen-specific B cell activation before using the immunized splenocytes as parental cells in cell fusion experiments. Mouse albumin and hemoglobin, actin (25 micrograms/ml), RNA polymerase II (5 micrograms/ml), as well as syngeneic mouse serum were used to immunize BALB/c spleen cells in vitro. We obtained antigen-specific PFC by using all of the different immunogens, including syngeneic mouse serum, and the in vitro immunized cells were then used in hybridization experiments. The specific efficiencies of each fusion that made use of cells immunized with mouse albumin, hemoglobin, syngeneic mouse serum, actin, or RNA polymerase II were 12, 31, 33, 52, and 22%, respectively, which illustrated the apparent lack of immune tolerance found when the immunization was performed in culture.