Immune dysfunction associated with graft-vs-host reaction in mice transplanted across minor histocompatibility barriers. II. Reversible defect in T-dependent antibody responses

B cell and Th cell functions were assessed in mice undergoing a graft-vs-host reaction (GvHR) in response to minor histocompatibility Ag by using the plaque-forming cell (PFC) response to the T-independent Ag TNP-Brucella abortus and the T-dependent Ag TNP-SRBC. Bone marrow plus spleen cells from B10.D2 mice were transplanted into lethally irradiated B10.D2 (syngeneic recipient) or H-2d-compatible BALB/c (allogeneic recipient) to produce a chronic form of GvHR. BALB/c recipients of an allogeneic transplant demonstrated a marked and proportional lymphoid depletion of the spleen with normal percentages of B cells, T cells, and CD4+ and CD8+ T cell subsets. Mice with GvHR made normal numbers of PFC/10(5) spleen cells in response to the T-independent Ag, but a significantly depressed number of PFC/10(5) spleen cells to the T-dependent Ag compared with normal B10.D2 mice and with irradiated B10.D2 recipients of syngeneic B10.D2 marrow plus spleen cells. Mice undergoing the minor Ag GvHR made significantly larger numbers of PFC/10(5) spleen cells after secondary immunization with TNP-SRBC compared with controls. In vitro assays demonstrated that B cells from mice with GvHR responded to T help from normal B10.D2 mice and that T cells from mice with GvHR provided help to normal B cells after in vivo immunization. These data demonstrate that radiation chimeras with GvHR in response to minor histocompatibility Ag have relatively normal B cell function and an apparent defect in T helper cell function that is reversible by immunization with appropriate Ag.

Minor transplantation antigens: their role in shaping the T cell repertoire

Minor transplantation, or histocompatibility (H), antigens are the targets of host-versus-graft (hvg) and graft-versus-host (gvh) reactions that occur when organs or tissues are exchanged between members of the same species who, although genetically not identical, are matched for their major histocompatibility complex (MHC) encoded transplantation antigens. Genes encoding minor H antigens map outside the MHC, on a number of different chromosomes. Whilst gvh and hvg reactions against individual minor H antigens are relatively weak, certainly in comparison with such reactions against MHC antigens, the presence of multiple minor H differences (the situation encountered in man) gives rise to very vigorous reactions that can endanger the survival of graft or host, or both. This is the pathological role of minor H antigens and, indeed, it was this role which was first designated to the MHC antigens, before their physiological role as guidance molecules for T lymphocytes was discovered. Recently, a potential physiological role for minor H antigens has been uncovered by the finding that the presence of certain minor H alleles in mice leads to removal in the thymus (negative selection) of all those T cells expressing a particular T cell receptor (TCR) gene. Such cells therefore never reach the periphery, where they might otherwise give rise to autoimmune reactions. The T cell repertoire is thus moulded by at least some minor H antigens, which may therefore be regarded as non-MHC immune response genes. Furthermore, T cell receptor usage by T cells specific for allogeneic minor H antigens appears not to be representative of T cell receptor usage in the peripheral pool.(ABSTRACT TRUNCATED AT 250 WORDS)

The mechanism of graft-host-tolerance in murine radiation chimeras transplanted across minor histocompatibility barriers

A better understanding of the mechanism(s) involved in graft-host-tolerance following allogeneic bone marrow transplantation is needed to develop new strategies to prevent graft-versus-host disease (GVHD). Based on previous studies, mainly in MHC-mismatched donor-recipient pairs, three hypotheses have been proposed: clonal deletion, active suppression and lack of adequate antigen-presenting cells. Our goal was to identify the mechanism(s) by which tolerance is achieved and maintained in radiation chimeras transplanted across minor histocompatibility barriers. Healthy (B6----LP) chimeras were obtained following injection of 10(7) C57BL/6 marrow cells to irradiated (9.5 Gy) LP hosts and used experimentally 100 days after chimerization. The tolerance state of (B6----LP) chimeras could not be abrogated after i.v. transfer of 5 x 10(7) donor-type spleen cells alone or with repeated i.p. injection of host-type antigen-presenting cells. No GVHD was observed when 10(7) marrow cells plus 5 x 10(7) spleen cells from (B6----LP) chimeras were injected to irradiated LP recipients. Chimera spleen cells suppressed GVHD when adoptively transferred to LP recipients of a C57BL/6 graft. These results suggest that in this model the presence of suppressor cells is both necessary and sufficient to maintain graft-host-tolerance.

Cellularly defined minor histocompatibility antigens are differentially expressed on human hematopoietic progenitor cells

Previously, five CTL lines directed against minor histocompatibility (mH) antigens designated HA-1-5 have been established from peripheral blood of patients after allogeneic bone marrow transplantation (BMT), and have been characterized using population and family studies. All cell lines showed specific HLA class I-restricted lysis of PHA-stimulated peripheral blood target cells from donors positive for the particular mH antigens. After 4 h of incubation of the mH antigen HA-3-specific CTL line with bone marrow cells from HA-3+ donors, complete class I-restricted inhibition of colony growth of the hematopoietic progenitor cells was observed even at low E/T ratios, indicating that the HA-3 antigen is strongly expressed on hematopoietic stem cells. Therefore, this antigen may be a target structure in the immune-mediated rejection of the hematopoietic graft in case of incompatibility for this determinant between donor and recipient in allogeneic BMT. In contrast, incubation of bone marrow cells with the antigen-specific anti-HA-1, -2, -4, and -5 CTL lines did not result in growth inhibition of the hematopoietic progenitor cells tested. After a prolonged incubation time and using a very high E/T ratio, progenitor cells from HA-2+ or HA-5+ donors were killed to some extent by the anti-mH-specific CTL lines, although the growth inhibition observed was minor and variable. Our results show that mH antigens are differentially expressed on human hematopoietic progenitor cells. Therefore, only some of these antigens may be targets in immune-mediated rejection of the bone marrow graft.

Cytotoxic T lymphocyte responses to minor H-43 alloantigens in H-43a and H-43b mice. Both anti-H-43b and anti-H-43a CTL activities are generated exclusively in the context of the same H-2Kb restriction element

We have previously demonstrated that anti-H-43a CTL response of H-43b responder mice was exclusively restricted by self H-2Kb (Kb) but not by the other nine self MHC class I alleles from independent origins, i.e., Kbml,d,k,s and Db,d,k,q,s. In the present study, we verified that Kf,q,r and Df,r alleles could also not serve as restricting class I elements in the CTL response to H-43a alloantigen. Another notable observation made in the earlier study was the fact that, in H-43 incompatibility of the alternative combination, H-43a mice were incapable of generating CTL activity against H-43b alloantigen. However, by means of employing new in vivo immunization procedures, we discovered that some but not all genetically identical H-43a responder mice could mount anti-H-43b CTL response restricted by self Kb. Again, no anti-H-43b CTL activity could be generated in the context of self Kk, Kj, Db or Dk molecules. Although the number of class I alleles we examined is still limited, these results indicate that antigenic fragments derived from the processed H-43a and H-43b alloantigens possess an indistinguishable epitope (agretope), and that such agretope either interacts only with the privileged Kb molecules or allows to bestow the immunogenic conformation of allodeterminants on the fragments solely in the context of the restricting Kb element.

Neonatal tolerance induction to Mlsa. II. T cells induce tolerance to Mlsa

We have investigated the ability of murine T cell lines to induce neonatal tolerance to Mlsa (minor lymphocyte stimulating). Mlsb mice were injected within 24 hr of birth with MHC (major histocompatibility complex) identical T cell lines generated by culturing responders from Mlsa strains with stimulators from Mlsb strains. Injected mice were tested at 6 to 8 weeks of age for responses in either primary mixed leukocyte reaction or IL-2 limiting dilution analysis. Mlsa specific responses by injected tolerant mice relative to noninjected controls were reduced by 92-98% in MLR and by 2- to 10-fold in IL-2 LDA. In contrast, responses against third-party MHC antigens by either the injected or the noninjected mice were identical. Fifty percent of all mice injected with the T cell lines were tolerant to Mlsa. These results strongly suggest that murine T cells express the Mlsa gene product.

Genetic aspects of the blood transfusion effect

The genetic requirements for the induction of the blood transfusion effect have been investigated in a genetically well-defined model. The survival of fully vascularized, heterotopic murine cardiac allografts was measured after a single preoperative transfusion of blood from mice selected to share MHC and/or minor histocompatibility (miH) antigens with the organ donor. The effect of a transfusion from a donor unrelated to the heart donor (third-party transfusion) on allograft survival was also determined. Five strain combinations were used for these experiments. The results obtained illustrate a number of important aspects of the blood transfusion effect in this model: (1) Donor-specific blood transfusion, where MHC and miH were shared by the blood donor and the organ donor, always induced prolonged graft survival. (2) The sharing of the whole MHC (H-2) by the blood donor and organ donor was found to be sufficient to prolong allograft survival in the five fully allogeneic strain combinations tested. (3) The sharing of miH antigens only was not sufficient to induce prolonged cardiac allograft survival. Special cases were identified showing that several factors could interact to potentiate the action of miH antigens in the induction of the blood transfusion effect. (4) Transfusion with blood from a third-party donor was effective in some strain combinations. In one recipient, blood from several third-party strains of mice, sharing neither MHC nor miH antigens with the organ donor, induced prolonged graft survival. We suggest that the mechanism by which third-party blood has a beneficial effect on graft survival is through crossreaction(s) between the blood donor and the organ donor. The results obtained in this study fit very well with one model for the cellular mechanism by which the transfusion effect may be mediated. This may be the means by which blood from randomly selected donors has a beneficial effect on graft survival in clinical transplantation.

Minor histocompatibility antigen H-Y is expressed on human hematopoietic progenitor cells

Polymorphic minor transplantation antigens probably play an important role in immune mediated graft rejections of bone marrow transplants. Mapping of these antigens on hematopoietic progenitor cells (HPC) is important since these antigenic determinants may serve as target structures in the rejection process, and it ultimately opens the possibility to match for these antigens. Using a cell-mediated cytotoxicity assay with H-Y-specific cytotoxic T lymphocytes as effector cells, a dose-dependent growth inhibition up to 100% of myeloid (CFU-GM), erythroid (BFU-E) and multipotential (CFU-GEMM) HPC of male donors was obtained, indicating expression of the H-Y antigen on these progenitor cells. In contrast, inhibition of relatively mature erythroid and myeloid progenitor cells was only 40-50%, indicating that the recognition of the H-Y antigen diminished during maturation of erythroid and myeloid HPC. Our results show that the H-Y antigen can be recognized on HPC as a target for cytotoxic T cell responses. This may be important in graft rejection of male donor bone marrow grafts by female recipients.

Genetic analysis of the presentation of minor lymphocyte stimulating determinants. I. Combined importance of MHC and non-MHC influences

In the course of studying the MHC restriction of minor lymphocyte stimulating (Mls) determinants, we observed that variation in the ability to present Mlsc determinants occurred with stimulator cells from different mouse strains that express the same class II MHC restricting elements; for example, one Iad-bearing strain, C3H.HTG, presented this non-MHC moiety, whereas another, C3H.OH, could not. As another example, the prototype Mlsb nonstimulatory H-2d stimulator cell, BALB/c, was shown to encode Mlsc even though it failed to trigger proliferation across this non-MHC barrier. In contrast, H-2d-compatible DBA/2 stimulator cells were capable of eliciting detectable levels of unprimed responder T cell proliferation across an Mlsc difference. Even when the BALB/c H-2d haplotype was replaced with the fully permissive H-2K halplotype, these BALB.K stimulator cells presented Mlsc (but not MHC) less effectively than H-2K-compatible C3H/HeJ stimulator cells. Analysis of the Mlsc-presenting capacity of stimulator cells obtained from (BALB.K x C3H) F1 x BALB.K first backcross and (BALB.K x C3H)F2 animals indicated that non-MHC-control influencing stimulatory ability of this non-H-2 Ag was multigenic. In addition, the capacity of DBA/2 to present Mlsa determinants more effectively than MHC-identical LT/ChReSv stimulator cells may indicate that the presentation of this Mls specificity is also influenced by non-MHC Ir genes. Thus the Mls phenotype of an animal should be considered the combined result of an Mls structural gene, the MHC haplotype, and multiple non-H-2 regulatory influences.

Failure of intravenously infused spleen cells bearing a minor histoincompatibility to delay rejection of skin grafts bearing additional antigens

Intravenous infusions of spleen cells bearing single minor H antigens have been shown to induce an antigen-specific prolongation of survival of subsequently applied skin grafts bearing the infused antigen. In this report it is shown that i.v. infusion of spleen cells bearing only H-Y as an alloantigen fails to prolong the survival of subsequently applied skin grafts bearing H-Y and additional H antigens. In contrast, others have shown that the i.v. infusion of alloantigen-bearing cells can inhibit DTH reactions, CTL generation, or organ allograft rejection directed against additional alloantigens, provided they are present in the challenge inoculum or graft together with the i.v.-infused antigens. Several possible reasons for the discrepancy between the results with skin grafts, and the results of others using different assays of responsiveness to H antigens are examined.

T cell recognition of Mlsc. I. Influence of MHC gene products in Mlsc-specific T cell recognition

Monospecific T cell clones have been proven to be powerful tools for the characterization of T cell recognition in many Ag-specific as well as allo-specific T cell responses. In this report, in order to elucidate the mechanism of T cell recognition of minor stimulating locus Ag (Mlsc) determinants, Mlsc-specific cloned T cells were employed together with primary T cell responses to clarify the role of MHC-gene products in Mlsc-specific T cell recognition. The results indicated that T cells recognize Mlsc determinants in conjunction with I-region MHC gene products. Moreover, certain MHC haplotypes (e.g., H-2a and H-2k) appear to function efficiently in the "presentation" of Mlsc, whereas other haplotypes (e.g., H-2b and H-2q) function poorly if at all in presenting Mlsc. Experiments with the use of stimulators derived from F1 hybrids between the low stimulatory H-2b, Mlsc strain, C3H.SW, and a panel of Mlsb, H-2-different or intra-H-2 recombinant strains strongly suggested that expression of E alpha E beta molecules on stimulators plays a critical role for Mlsc stimulation. The functional importance of the E alpha E beta product in Mlsc recognition was further demonstrated by the ability of anti-E alpha monoclonal antibody to inhibit the response of cloned Mlsc-specific T cells. Inhibition of the same Mlsc-specific response by anti-A beta k antibody suggests that the A beta product may also play a role in T cell responses to Mlsc.

Neonatal thymus provides all the information required for tolerance induction against all the non-thymic organ-specific minor histocompatibility antigens

Using our original "in vivo MLR" technique, we demonstrated that B10.D2 cells grafted into irradiated (DBA/2 x B10.D2)F1 mice (H-2d/H-2d) were stimulated to divide by the whole non-H-2 minor histocompatibility antigens (MiHA) of the DBA/2 background in each organ where these MiHA are expressed. When B10.D2 cells were grafted into N7 mice (generation descending from six successive backcrosses with B10.D2 after an initial cross DBA/2 x B10.D2) which had kept 1/64 of the DBA/2 genetic background, a lack of correlation between the levels of stimulation in the different organs of the same mouse was demonstrated. We established that the number of expressed MiHA lies between 7 and more than 100, depending on the organ, and that the organ specificity is a feature of the expression of these MiHA. Furthermore, using a different technique, we demonstrated that B10.D2 T cells can acquire a specific tolerance state towards the whole DBA/2 antigen background throughout maturation and differentiation in a fully syngeneic environment with the exception of a neonate-(DBA/2 x B10.D2)F1 grafted thymus. We concluded, therefore, that all information corresponding to the adult- and organ-specific MiHA is available in the neonatal thymus. Three working hypotheses are proposed to reconcile the two lines of results.

Antigraft responses to the H-28c antigen by B6 and B6D2F1 mice

The survival of minor H antigen-bearing skin grafts from donors congenic with C57BL/6 (B6) was compared in B6, B6D2, and AB6 hybrid recipients. In a case singled out for further study, B6 mice were found to reject HW110 skin (H-28c antigen) rapidly, whereas B6D2 mice rejected HW110 skin much more slowly and variably. Both major histocompatibility complex (MHC)-linked and non-MHC genes appeared to affect the survival of HW110 strain skin grafts on B6 and B6D2 recipients. Results of several experiments appear to rule out the sharing of H-28c epitopes between donors and recipients as an explanation for the relatively poor response of B6D2 mice to HW110 skin grafts. Experiments involving bone marrow chimeras produced by the reciprocal exchange of bone marrow between irradiated B6 and B6D2 mice suggest that bone marrow-derived donor cells and non-bone-marrow-derived host cells each contribute to the immune response phenotype with respect to the H-28c antigen. An attempt was made to determine whether B6D2 mice that failed to reject HW110 strain skin grafts possessed suppressor cells specific for the H-28c antigen. Spleen cells from poorly responsive B6D2 mice failed to suppress the rejection of HW110 skin grafts when assayed in immunodeficient mice that were provided with cells from immune B6D2 donors that were highly responsive to HW110 skin grafts.

Effector mechanism in rejection of allografts expressing an isolated minor histocompatibility disparity. Importance of cytotoxic T lymphocytes in the rejection of H-43a allografts by H-43b mice

To explore effector mechanisms in allograft rejection, we transplanted skin grafts (SG) across a single minor histocompatibility locus (H-43) using mouse strains carrying the H-43b allele as SG recipients and those carrying the H-43a allele as SG donors. Recipients' spleen cells (SC) were assayed at various intervals for 200 days for anti-H-43a cytotoxic T lymphocyte (CTL) responsiveness, as well as delayed-type hypersensitivity (DTH) responsiveness. When H-43a SG from C3H.SW mice were transplanted to H-43b CWB mice, two thirds of the recipients rejected the SG, and recipients' SC showed marked self-H-2Kb-restricted anti-H-43a CTL responsiveness until the end of the observation period. In contrast,H-43aSG transplanted to H-43b (B10.BRxCWB)F1 (BWF1) mice survived in almost all of the BWF1 recipients. The anti-H-43a CTL responsiveness of the recipients' SC was evident until day 40 but thereafter started to wane and eventually disappeared. Notably, BWF1 mice whose self-H-2Kb-restricted anti-H-43a CTL precursors had been primed by prior injection with H-43a SC rejected H-2Kb-bearing H-43a CSW SG but not H-2k, H-43a C3H/HeN SG. In contrast, an anti-H-43a DTH response was not induced in any of the CWB and BWF1 recipients, including CWB recipients who rejected the H-43a SG. Since it has been well documented that anti-H-43a CTL are restricted solely by self-H-2Kb, the results in this study indicate that self-H-2Kb-restricted anti-H-43a CTL are responsible for rejection of H-43a allografts by H-43b recipient mice.

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.

MHC-unrestricted T-cell cytotoxicity against tumour cells

F9 embryonal carcinoma cells (EC) grow as tumours in their strain of origin, 129/Sv, but can be rejected by mouse strains differing at the H-2 and/or non-H-2 loci. The presence of H-2 class I and/or minor H antigens on F9 and other EC cells is implied by (i) the rejection of EC cells by mice immunized with appropriate H-2 class I transfectants, and (ii) the ability of appropriate EC cells to prime mice for second-set in vivo skin-graft rejection responses to H-Y, and secondary MLC responses to multiple minor H antigens. However, EC cells express no H-2 class I antigens in vitro, and for in vivo rejection by T-cell responses directed either at allogeneic class I molecules or at minor H antigens restricted by self class I molecules, one would need to postulate that EC cells growing in vivo could express sufficient class I antigens for recognition by T cells. In the course of investigating this question, we found evidence for class I expression but also evidence for an additional antigen(s), shared by EC and tumour cells and recognized in a non-MHC-restricted manner.

Histological changes of bile duct in experimental graft-versus-host disease across minor histocompatibility barriers. II. Electron microscopic observations

Electron microscopic features of intrahepatic bile ducts of experimental mouse graft-versus-host disease (GVHD) across minor histocompatibility barriers were studied for 14 months after transplantation. In GVHD mice, the bile duct epithelial layer was consistently infiltrated by lymphoid cells and often accompanied by polymorphonuclear leukocytes, monocytes and rarely by plasma cells. The epithelial cells in close contact with and in the vicinity of these infiltrated cells showed a variety of degenerative changes, including darkness of the cytoplasm and the nucleus with shrunken, irregular contours, increase in the amount of endoplasmic reticulum and number of mitochondria, and formation of intracytoplasmic vesicles and diverticula, cytoplasmic blebs, and apoptopic bodies. Lymphocytes were in close contact with epithelial cells through a number of point-contacts and located in the lateral intercellular spaces and/or between the basement membranes and the epithelial cells. The localization of infiltrating lymphocytes beneath the epithelial cells with conspicuous detachment from the basement membranes strongly suggested a link with subsequent epithelial cell injury and death. The lymphoid cells had irregular cytoplasmic projections which occasionally extended into spaces created by retractions of the epithelial cell membranes, reflecting an activation of the lymphocytes. These findings support the notion that the bile duct lesions in GVHD across minor histocompatibility barriers are mediated by specifically sensitized lymphocytes against epithelial cell membrane antigens. From our previous finding that a large majority of the infiltrating lymphocytes had a phenotype of helper/inducer T cells, a putative role of these lymphocytes in the induction of the bile duct lesions is discussed.

Time-response studies of the cellular immune response to cell membrane antigens

It was the objective of these experiments to study the time-related changes in the responsiveness of the cellular elements of the immune system following contact with single non-H-2 or multiple H-2 histocompatibility antigens. The reactivity of spleen cells from mice that received injections of spleen cells bearing H-1c, H-3c, H-13a, or H-2b cell membrane alloantigens was characterized at intervals following antigen contact. Spleen cells taken from mice not receiving injections showed no in vitro proliferative or cytolytic responsiveness to cells bearing individual non-H-2 antigens; after in vivo antigen contact with single non-H-2 antigens there was an interval of specific cellular unresponsiveness followed by alternating periods of responsiveness and unresponsiveness. The duration of the unresponsiveness immediately following injection correlated with the strength of the injected antigen--specifically, the stronger the antigen, the shorter the period of unresponsiveness. The data indicate fluctuation in the level of helper T lymphocyte activity, as well as cytotoxic T lymphocyte activity. In contrast, in vitro responsiveness elicited by H-2b antigens with and without prior in vivo antigen contact was of a similar magnitude, and both persisted at a relatively constant level. Suppressor mechanisms were not studied. Of particular interest was the observation that in vivo contact with non-H-2 antigens resulted in suppression of spleen cell production of IL-2 in response to lectin stimulation and fluctuation in the magnitude of the primary response of cytotoxic T lymphocytes to H-2 antigens.

Cytotoxic T lymphocyte response to minor H-43a alloantigen in H-43b mice. Privileged H-2Kb restriction to the response is not due to immunodominance or epistatic effect but due to Ir gene function of H-2Kb itself

Previous study demonstrated that anti-H-43a cytotoxic T lymphocyte (CTL) response of H-43b CWB (H-2b) stain carrying non-major histocompatability complex (MHC) genes of C3H and F1 strains raised by crossing CWB with various H-43b strains was restricted exclusively by self H-2Kb (Kb). In the present study, newly produced C3W strain (H-2k, H-43b), which is H-43-congenic to C3H/HeN (H-2k, H-43a), was used as H-43b mice, and possibility of immunodominance of Kb was examined. No anti-H-43a CTL response could be induced in C3W strain and F1 strains raised by crossing C3W with other H-43b strains not carrying Kb. Thus, the possibility of immunodominance of Kb over the other MHC class I alleles could not be supported. We also examined possibility of epistatic effect of I region genes and non-MHC genes on the Kb restriction. (C3W x C57BL/6)F1(I-Ak/b) and (C3W x B6.CH-2bm12)F1(I-Ak/bm12)mice showed equally anti-H-43a CTL response restricted exclusively by self Kb, and (C3W x B10.MBR)F1(Ik/k) mice also showed anti-H-43a CTL response restricted solely by self Kb. Cold target competition experiments demonstrated that H-43b C57BL/10 or A.BY mice, which do not have non-MHC genes of C3H mounted anti-H-43a CTL response restricted solely by self Kb. Thus, no relation of I region genes or non-MHC genes to the Kb restriction was shown. All the results indicate that H-43b mouse strains, including F1, can not achieve anti-H-43a CTL response unless they carry Kb allele. Notably, (C3W x C57BL/6)F1 mice mounted self Kb-restricted anti-H-43a CTL response, whereas (C3W x B6.CH-2bm1)F1 mice carrying mutated Kb could not mount anti-H-43a CTL response at all. These findings indicate strongly that Kb itself is classical Ir gene of anti-H-43a CTL response and directs self Kb restriction of the response.