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.     

Correlation of mixed lymphocyte reactivity and skin graft rejection in nonhuman primates.

One-way mixed lymphocyte culture (MLC) reactivity and skin graft rejection were investigated to assess immune competence and histocompatibility in the baboon, the cebus monkey, and the cotton-topped marmoset. Adequate and comparable cell-mediated immunity was demonstrated. MLN reactions revealed strong histocompatibility differences among the three primate species and stimulating alloantigens for unrelated individuals of each species. Xenogeneic skin grafts survived nine days and allogeneic grafts, an average of 11 days. These systems appear readily applicable for assessing histocompatibility in nonhuman primates.     

Synergistic interactions between lymph node and thymus cells in response to antigenic differences limited to selected regions of the H-2 complex.

Thymus and lymph nodes from the A.TL recombinant line were utilized as sources of responding cells in MLR (mixed lymphocyte response) assays to MHC-determined (major histocompatibility complex) antigenic differences. Cells from both sources were stimulated to proliferate by antigenic determinants controlled by the H-2K region alone, H-2D region and the H-2I-H-2S regions. Nylon-fiber-adherent splenic cells from each of the stimulating cell strains stimulated T-cell-dependent responses. Synergistic interactions between A.TL thymus and lymph node cells were initiated by antigenic products limited to single H-2 regions. Antigenic differences determined within the H-2I region were not required for synergistic responses to H-2K-controlled products or for the generation of cytotoxic killer cells to H-2D-associated antigens. The H-2I-region-associated products also were very effective in stimulating T-cell synergy. These data demonstrate that the two responsive T-cell subpopulations can both be stimulated by alloantigens coded within a single known H-2 region.     

Syngeneic mixed lymphocyte reaction in mice: strain distribution, kinetics, participating cells, and absence in NZB mice.

Co-culture of mouse spleen nonadherent (T-enriched cells with mitomycin C-treated unfractionated syngeneic spleen cells resulted in increased DNA synthesis in the responding T cells. The kinetics of this syngeneic mixed lymphocyte reaction (SMLR) showed that peak DNA synthesis occurred on day 5 of culture compared to day 4 for conventional mixed lymphocyte reaction (MLR). Anti-T cell antiserum plus complement treatment of the responding cell population abolished the reaction, and similar treatment of the stimulator population enhanced SMLR. These studies indicate that SMLR represents the response of T cells to non-T cells. Studies on the generation of cytotoxic T lymphocytes (CTL) in parallel cultures of T cells activated by syngeneic or allogeneic spleen cells showed no cytotoxicity of SMLR-activated cells for either PHA- or LPS-induced blasts but did show a good CTL response of allo-activated cells to both targets. Studies on the strain distribution of SMLR revealed that NZB mice manifested poor or no stimulation in SMLR whereas all other strains tested exhibited strong SMLR. This defect in NZB mice may be pathogenetically related to the autoimmune disease that develops in these mice.     

Xenogeneic mixed leucocyte response

Xenogeneic mixed leucocyte cultures composed of human, chimpanzee, baboon, goat, sheep, pig, and dog cells were set up with a variety of plasma culture supplements. The characteristics of the human leucocyte response to xenogeneic cells was similar to its response to allogeneic cells. Peak response to xenogeneic stimulation occurred on the same culture day as the peak response to allogeneic stimulation. Similar numbers of xenogeneic and allogeneic cells produced peak stimulation of cells from any one individual. There was, however, a wide variation in the response of human lymphocytes to both allogeneic and xenogeneic cells. A factor in the plasma supplement specific for responding or stimulating cells inhibited the mixed leucocyte response in some combinations and could be removed by absorption techniques.     

Alteration of the antigenicity of human lymphocytes by plant lectins and short-term tissue culture.

Human lymphocytes studied after being placed in culture for 1–6 wk progressively lost stimulating ability, i.e., lymphocyte defined antigens, when tested in one way mixed lymphocyte culture (MLC) but retained several other identifiable membrane components as well as the capacity to respond to mitogenic stimuli. Lymphocytes placed in culture with motogenic doses of PHA and Con-A after 1 and 2 wk strongly stimulated autologous responding fresh lymphocytes, but the MLC response of allogeneic fresh lymphocytes to stimulating lectin treated cells was even lower than the response to stimulating allogeneic cultured lymphocytes. The HL-A antigens on lectin treated cells or on lymphocytes through 6 wk in culture were clearly identifiable. Assays for T cell rosettes and B cell surface immunoglobulin showed both cell types to be present in numbers equal to fresh lymphocytes for up to 5 wk after culturing. However, the Fc receptor site on B cells was lost from cultured lymphocytes at the same time that MLC stimulation was lost. It is concluded that plant lectins can unmask new mitogenic sites on the cell surface as well as mask or delete existing sites, and that culturing lymphocytes for 1–6 wk will produce somewhat similar modulations. Modulation of surface membrane components by tissue culture or lectins may, therefore, have a profound effect in altering transplantation immunogenicity.     

Induction of suppressor cells in autologous mixed lymphocyte culture (AMLC) in humans

T cells stimulated for 6-7 days in autologous mixed lymphocyte culture (AMLC) showed suppressive effects when added to fresh mixed cultures where autologous lymphocytes (A) were stimulated by Mitomycin C-treated allogeneic lymphocytes (Xm), in a ratio of A:Xm:AMLC-activated cells of 1:1:0.5. Both cytotoxic and proliferative activities in second cultures, as assayed after 6 days of incubation, were significantly inhibited (percentage suppression of cytotoxic activity observed in 17 experiments was 75.3 +/- 22.4; percentage suppression of proliferation was 60.6 +/- 18.2). Suppressor cells (SC) generated in AMLC were Mitomycin C sensitive and nonspecific in their action; not only A/Xm but also X/Am and X/Ym cultures were suppressed to the same extent. AMLC-Activated cells showed a considerable degree of proliferation in response to alloantigens but failed to express any cytotoxic activity against autologous or allogeneic phytohemagglutinin blasts. Thus, the inhibitory effect observed in this system is not due to cytotoxic elimination of responding or stimulating cells in the second culture but rather reflects a true regulatory (suppressive) mechanism.     

Restriction by the major histocompatibility complex of antigen-induced T lymphocyte proliferation in new inbred guinea pig strains.

Employing new inbred guinea pig strains, JY 1, JY 2 and JY 3, established in this Institute in addition to strains 2 and 13, the authors investigated histocompatibility restriction in macrophage-T lymphocyte interaction. These five strains are known to possess distinct major histocompatibility complex (MHC) gene profiles (1, 2). This fact was supported by our results concerning the mixed leukocyte reaction (MLR) and cytotoxicity test with alloantisera. Using various combinations of T lymphocytes and peritoneal exudated cells (PECs) from these strains, in vitro proliferative responses of T lymphocytes from BCC-immune animals to PPD-pulsed normal PEC were tested. Successful activation of T cell response was observed not only in syngeneic combinations but also in allogeneic combinations among strains JY 1, JY 3 and strain 13 which share common Ia antigens detected by strain 2 anti-strain 13 alloantiserum. Because JY 1 and JY 3 seem to share a common B antigen differing from strain 13, it was suggested that identification in the I region of MHC is sufficient for effective antigen-presentation by the macrophage. Although a part of Ia is shared, no T lymphocyte activation was observed in the combination between JY 2 and JY 1 or JY 3, whereas strong MLR occurred in these allogeneic combinations. At the present stage of the study, it can be said that disparity in the part(s) of Ia antigens which is responsible for strong MLR cannot lead to effective T cell-macrophage interaction. These results support the concept that functional activation of primed, proliferating T lymphocyte requires the participation of gene products of macrophages coded for by the I region in MHC. By employing JY 1, JY 2 and strain 2, which appear to possess distinct B and Ia antigens, it was shown that the T lymphocyte and macrophage interactions essential for mitogen-induced T lymphocyte proliferation are not restricted by histocompatibility.     

Regulation of immune response in allogeneic mixed spleen cell cultures. I. Influence of I-region on the generation of suppressor cells

The immune responses of allogeneic mixed spleen cell cultures (MLC) to the T-dependent antigen, SRBC, and to the T-independent antigen, DNP-PAA, were investigated. The immune response to DNP-PAA in MLC with certain strain combinations was always suppressed as compared with the expected PFC response calculated from the PFC responses of the individual strains. This suppression was eliminated by treating the spleen cells with RAMB antiserum plus complement before the incubation of the MLC with DNP-PAA. It can be concluded that the suppression in the PFC response to the T-independent antigen DNP-PAA in MLC is due to the generation of suppressor T-cells. The PFC response to the T-dependent antigen, SRBC, in MLC showed either suppression, no change, or rarely augmenation, suggesting that the allogeneic mixed spleen cell cultures can generate both suppressor and helper T cells and that the balance between helper and suppressor activity regulates the PFC response to a T-dependent antigen. Suppressor activity was also generated in a one-way MLC, but the degree of suppression depended upon which of the two strains was responding. Similar amounts of thymidine were incorporated in the one-way MLR irrespective of which strains was responding. Thus, the extent of proliferation in one-way MLR is not related to the degree of suppressor activity generated. The results further indicate that a difference between two strains in the I-C, S, and G regions of the major histocompatibility complex is required to generate suppressor activitiy that can depress the response to a T-independent antigen, MLC between strains differing in K, I-A, I-B, I-J, I-E, and D regions generate little or no suppressor activity in this system.     

Isogeneic and allogeneic lymphocyte interactions may be controlled by cell surface immunoglobulin tropism.

A study of allogeneic MLC (mixed lymphocyte culture) and two types of isogeneic MLC has been conducted in which subsets of B-cells were serologically removed from pools prior to using the remainder as stimulator cells. Cellular division in the two types of ILC (isogeneic lymphocyte culture) was found to be triggered by lymphocytes with IgG₁ on their surfaces. In contrast, the stimulator cells in ALC (allogeneic lymphocyte culture) possessed membrane-bound IgG_2A and/or possibly IgG_2B. Splenic T-cells were incapable of stimulating replication of splenic or lymph nodal T-cells in the absence of B-cells. Splenic T-cell preparations served as weak stimulators of other allogeneic T-cells but only when B-cells, either isogeneic or allogeneic to the stimulator T-cells, were present. We propose that stimulation in the MLC occurs in two distinct steps. First, immunoglobulins on cell surfaces may function to bring appropriate subsets of cells together. Next, antigenic recognition occurs that results in blastogenesis. Furthermore, the tropism or attraction that certain immunoglobulins have for some cell types may determine which subsets of cells participate in allogeneic and which take part in isogeneic MLC.     

HLA class l specific t lymphocyte clones with dual alloreactive functions

Four human T lymphocyte clones exhibiting proliferative responses to class I HLA antigens were isolated from an in vitro mixed lymphocyte culture (MLC). Three clones expressed the Leu-2⁺3^– phenotype and demonstrated proliferation in response to HLA-B8, while the fourth clone expressed the Leu-2^–3⁺ phenotype and proliferated in response to HLA-A2. These clones were also cytotoxic towards cells bearing the same target antigens. Blocking studies utilizing monoclonal antibodies demonstrated that proliferation was triggered by determinants on the class I molecule itself, and these determinants appear to be spatially close to those which determine serologic allospecificity. These findings support the concept that the class I molecules themselves are the weak MLC stimulating determinants previously mapped to the HLA-A and B regions of the major histocompatibility complex.Abbreviations used in this paper B-LCL B-lymphoblastoid cell line - cpm counts per minute - FCS fetal calf serum - HS human serum - ³H-TdR tritiated thymidine - IL-2 interleukin-2 - IL2-CM interleukin-2 containing conditioned medium - MHC major histocompatibility complex - MLC mixed lymphocyte culture - MoAb monoclonal antibody - PBL peripheral blood mononuclear leukocytes - PLT primed lymphocyte test     

Blocking of MLC stimulation by anti-Ia sera: studies with the virus plaque assay.

The development of congenic mouse strains identical at the H-2K and H-2D loci but differing by I-region associated (Ia) determinants has permitted an association to be established between Ia determinants and stimulation in mixed lymphocyte culture reactions (MLR). The present experiments were undertaken to establish whether the Ir-coded control of MLR operated at the level of recognition or of stimulation. Reciprocal MLR were established between A.TH and A.TL mouse spleen cells in the presence or absence of anti-Ia sera directed either at determinants of the stimulating or responding cells. The number of T cells responding was assessed by the virus plaque assay. Anti-Ia sera directed against the responding cells were no more inhibitory of the MLR than normal mouse serum. In contrast, anti-Ia sera directed against determinants of the mitomycin-treated stimulating cells markedly inhibited activation of T cells in the MLR.     

Differential allo-response of murine thymocytes to H- 2 K region different recombinants and to H-2Kb mutants

Thymocytes used as responding cells in a mixed leukocyte culture with x-irradiated splenic stimulating cells generate highly significant proliferative and cytotoxic responses when responding and stimulating cells differ by the entire H-2 complex. On the other hand, when the genetic difference between responding and stimulating cells is only a K region, very little, if any, proliferative response is detectable and no cytotoxic response is found. In contrast, when responding and stimulating cell donors differ by a spontaneous mutation in the K region of the H-2 complex, as found in B6.C-H-2ba, B6-H-2bd and B6.C-H-2bf, highly significant proliferative and cytotoxic responses can be obtained. These results, thus, argue that the H-2 mutants cannot, with regard to their relationship to the parental strain, be readily equated with a K region difference as defined in the recombinant inbred strains.     

Human immunodeficiency disease: impairment of cellular interactions leading to abnormal mediator production in mixed lymphocyte culture reaction.

Leukocyte migration inhibitory factor (LMIF) production in mixed lymphocyte culture (MLC) reactions is the result of cellular interactions based on two separate phenomena: the capacity of lymphocytes to stimulate in MLC, and the capacity of lymphocytes to respond in MLC. Puromycin-treated lymphocytes are capable of stimulating allogeneic cells for LMIF production, but are unable to respond with synthesis of LMIF (one-way MLC-LMIF test). We have studied the stimulating and responding capacity of lymphocytes from patients with different immunodeficiency syndromes in a one-way MLC-LMIF assay. Lymphocytes from patients known to have qualitative and quantitative defects of T cell or B cell functions (Hodgkin's disease, mycosis fungoides, thymoma, chronic lymphatic leukemia) were found to respond poorly as measured by mediator production although their stimulating fuction was frequently retained. Patients with advanced solid tumors often had both MLC-stimulating and responding functions depressed. There was no apparent correlation between mitogen response and MLC-induced LMIF responses or between MLC proliferative response (as measured by thymidine incorporation) and mediator production. Studying of stimulatory and responding capacity of lymphocytes in the MLC-LMIF assay provides a new tool for assessing immunocompetence and allows for in vitro evaluation of cellular interactions that may play an important role in vivo.     

LY-2+ effectors cytotoxic for syngeneic tumor cells: generation by allogeneic stimulation and by supernatants from mixed leukocyte cultures

The present study was aimed at gaining insight into means by which stimulation of mouse spleen cells with allogeneic normal cells in mixed leukocyte cultures (MLC) can result in the generation of effector cells cytotoxic for syngeneic tumor or transformed cells. Stimulation of lymphocytes from BALB/c or C3H mice for 5 days with cells from mice of every allogeneic strain tested, in medium containing mouse serum and lacking xenogeneic serum, resulted in the activation of effectors cytotoxic for syngeneic cells transformed spontaneously or by SV40, polyoma or adenovirus. In each experiment, all of the syngeneic transformed cell lines, as well as clones derived from these lines, were lysed to the highest degree by effectors obtained from the same culture, and therefore stimulated with cells from the same allogeneic strain. Although the particular allogeneic sensitizing strain that induced the highest cytolytic activity varied between experiments, effectors obtained from the culture with the highest cell recovery always exhibited the greatest cytotoxicity against all the syngeneic transformed cells and clones. Lysis was mediated predominantly by Ly-2+ effectors; total lytic units of cytotoxicity recovered after treatment with monoclonal anti-Ly-2 antibody and complement (C) were reduced by 85 to 90% compared to cells treated with C alone. Lysis of syngeneic tumor cells by the allosensitized effectors in cytotoxicity assays was not inhibited by the addition of unlabeled "blocking" lymphocytes from the allogeneic strain used for sensitization. In addition, it was found that lymphocytes cultured without stimulating cells for 5 days in medium supplemented with supernatants from secondary MLC that are known to contain high levels of lymphokines, mediated high levels of cytotoxicity on all the transformed cells tested, but lacked detectable cytotoxic activity for syngeneic or allogeneic Con A blasts. The MLC supernatant-activated effectors that lyse the transformed cells are phenotypically CTL, because treatment with anti-Ly-2 and C reduced lytic activity by approximately 75%. Taken together, these findings suggest that the generation in MLC of Ly-2+ effector cells cytotoxic for syngeneic transformed cell lines might not be due, in some cases, to lymphocyte responses to particular alloantigens on the stimulating cells that are cross-reactive with "alien" histocompatibility antigens on transformed cells, but rather is due to effector cell activation by lymphokines produced during allogeneic stimulation.     

Absence of a significant mixed lymphocyte reaction in a marsupial (Monodelphis domestica)

Previously we reported preliminary results suggesting that the marsupial Monodelphis domestica fails to exhibit a mixed lymphocyte reaction with allogeneic lymphocytes. To test whether this observation is simply a matter of a response too weak to detect, but capable of being augmented by immunization, we performed mixed lymphocyte culture tests on 23 of these animals that had been immunized with lymphocytes. Despite the fact that all recipients were sensitized to the lymphocytes of the donors, none of the animals had a substantial mixed lymphocyte response. Significant stimulation was noted with the mitogen concanavalin A; thus, the T cells were immunologically competent. It seems likely that the failure of this species to exhibit a significant mixed lymphocyte response is due to T cells whose ontogeny differs from that of the T cells of eutherian mammals.     

Identical genetic control of MLC reactivity to different MHC incompatibilities,independent of production of and response to IL-2

The inbred strain STS/A exhibits a higher proliferative response in the mixed lymphocyte culture (MLC) to stimulator cells of all 11 tested inbred mouse strains with 10 different major histocompatibility complex (MHC) haplotypes, as well as to stimulation with IL-2 than does the strain BALB/cHeA. However, alloantigen-stimulated BALB/c cells produce more IL-2 than STS/A cells. To study the genetic basis of these differences, we used 20 recombinant congenic strains (RCS) of the CcS/Dem series. Each of these CcS/Dem RC strains contains a different subset of about 12.5% of genes from the STS/A strain and the remaining approximately 87.5% of BALB/c origin genes. As a result the multiple non-linked genes responsible for phenotypic differences between BALB/c and STS/A became separated into different CcS/Dem strains. The strain distribution pattern (SDP) of high or low MLC response of individual CcS/Dem strains to stimulator cells of four different strains was almost identical, indicating that differences in responsiveness, rather than the alloantigenic difference itself, determine the magnitude of the response, and that the responsiveness to different alloantigens is largely controlled by the same genes. The SDP of IL-2 stimulation was different from that of MLC responsiveness. The differences in the proliferative responses observed among individual CcS/Dem strains were not due to differences in numbers of CD3⁺, CD4⁺ or CD8⁺ cells or to the observed differences in IL-2 production, and hence they likely reflect genetically determined intrinsic properties of T cells. These results show that a set of non-linked genes controls proliferative responses in MLC irrespective of the MHC haplotype of the stimulator cells, and that stimulation with IL-2 and production of IL-2 are controlled by different subsets of genes. Since the genomes of all RCS are extensively characterized by microsatellite markers, they can be used to map the genes controlling proliferative responsiveness to stimulation with alloantigens and IL-2.     

The allogeneic effect: M-locus differences substitute for differences in the H-2 major histocompatibility complex.

The primary immune response against sheep red blood cells in T cell-deficient spleen cell cultures from nude mice was tested in the absence and presence of allogeneic spleen cells. The allogeneic spleen cells differed either in regard to the major histocompatibility complex (H-2) or only with respect to the M-locus. Surprisingly the M-locus different spleen cells were almost as efficient in enhancing the anti-sheep red blood cell response in nude cultures as were the cells differing on the complete H-2 complex. Evidence is presented that AKR anti-theta serum sensitive T cells are responsible for the M-locus-dependent effect edscribed. This effect is shown to be mediated by a factor released from actived T cells stimulated in M-locus different mixed lymphocyte cultures. Since almost identical parameters have been observed in both the M-locus-dependent situation as in the "classical" allogeneic situation we concluded that an allogeneic effect can be induced by T cells responding to a complete set of the major histocompatibility complex (H-2) as well as to lymphocyte-activating determinants (M-locus) alone.     

Antigen-specific xenogeneic CTL activity in the Syrian hamster

Previous studies of the Syrian hamster have demonstrated a lack of cytotoxic T lymphocyte (CTL) activity in vaccinia virus-infected animals. Our laboratory has reexamined CTL activity in both the classical inbred strains, MHA, CB, and LSH, as well as the recently inbred strain MIT. Primary and secondary CTL specific for the immunizing antigen have been detected after in vitro culture in MIT but were not demonstrable in the classical strains. Only lymph node cells of the responding animal demonstrated this activity, spleen cells being phenotypically devoid of such a response. Identification of the cell responsible for cytolysis as a T cell was demonstrated by nylon wool nonadherence, specificity on Con A blasts, and the lack of surface immunoglobulin, as demonstrated by cell-sorter analysis.     

3H-thymidine paper strip modification of the lymphocyte transformation test. III. Whole blood lymphocyte mixed culture using a cryopreserved stimulating cell mixture

In comparison to the classical mixed lymphocyte culture (MLC) method a MLC technique using whole blood cultures of responding cells and a pool of prepared stimulating cells from 10 healthy blood donors is described. The reproducibility of cryopreservation of stimulating lymphocytes was proven by means of cell electrophoresis.