Kidney transplantation between congenic versus standard inbred strains of rats: I The significance ofH-1 and non-H-1 gene differences

Concepts of “antigenic strength” in organ transplantation have been evaluated in relation to orthotopic kidney allografts inH-1 congenic strains of rats. Untreated recipients reject fully allogeneic kidneys possessing singleH-1 differences as acutely as kidneys displaying multiple histocompatibility differences. Heterozygozity for H-1 specificities as well as for H-1 plus non-H-1 specificities (semiallogeneic kidneys) favors long term survival (autoenhancement), especially when the specific immune response genes of the recipient lead to reduced reactivity. In active enhancement, the transplantedH-1 congenic kidneys, devoid of additional weak antigens, retain prolonged functional integrity. Weak non-H-1 antigens substantially influence the successful establishment of specific enhancement in an adverse way, either as additive immunogens or as target sites for the effector arm of the rejection response.     

IFN-gamma alters the pathology of graft rejection: protection from early necrosis

We studied the effect of host IFN-gamma on the pathology of acute rejection of vascularized mouse heart and kidney allografts. Organs from CBA donors (H-2k) were transplanted into BALB/c (H-2d) hosts with wild-type (WT) or disrupted (GKO, BALB/c mice with disrupted IFN-gamma genes) IFN-gamma genes. In WT hosts, rejecting hearts and kidneys showed mononuclear cell infiltration, intense induction of donor MHC products, but little parenchymal necrosis at day 7. Rejecting allografts in GKO recipients showed infiltrate but little or no induction of donor MHC and developed extensive necrosis despite patent large vessels. The necrosis was immunologically mediated, since it developed during rejection, was absent in isografts, and was prevented by immunosuppressing the recipient with cyclosporine or mycophenolate mofetil. Rejecting kidneys in GKO hosts showed increased mRNA for heme oxygenase 1, and decreased mRNA for NO synthase 2 and monokine inducible by IFN-gamma (MIG). The mRNA levels for CTL genes (perforin, granzyme B, and Fas ligand) were similar in rejecting kidneys in WT and GKO hosts, and the host Ab responses were similar. The administration of recombinant IFN-gamma to GKO hosts reduced but did not fully prevent the effects of IFN-gamma deficiency: MHC was induced, but the prevention of necrosis and induction of MIG were incomplete compared with WT hosts. Thus, IFN-gamma has unique effects in vascularized allografts, including induction of MHC and MIG, and protection against parenchymal necrosis, probably at the level of the microcirculation. This is probably a local action of IFN-gamma produced in large quantities in the allograft.     

The genetic control of the immune response to murine histocompatibility antigens

The genetic control of the immune response to H-4 histocompatibility alloantigens is described. The rejection of H-4.2-incompatible skin grafts is regulated by anH-2-linkedIr gene. Fast responsiveness is determined by a dominant allele at theIrH-4.2 locus. TheH-2 ^b ,H-2 ^d , andH-2 ^s haplotypes share the fast response allele;H-2 ^a has the slow response allele. Through the use of intra-H-2 recombinants, we have mapped theIrH-4.2 locus to theI-B subregion of theH-2 complex; theH-2 ^h4 ,H-2 ¹⁵, andH-2 ^t4 haplotypes are fast responder haplotypes. These observations suggest that the strength of non-H-2 histocompatibility antigens is ultimately determined by the antigen-specific recipient responsiveness.     

Review lecture. Immunology of H-Y antigen and its role in sex determination

H-Y was originally discovered as a transplantation antigen that caused female mice of certain inbred strains to reject skin from otherwise identical males. The ability to make the skin graft rejection response and, in vitro, cytotoxic T cell responses against H-Y is controlled by genes within the major histocompatibility complex, H-2, and by non-H-2 genes. H-Y belongs to a class of weak transplantation antigens characterized by an inability to elicit responses under many conditions. Although genetic factors are very important in determining responsiveness, their action can be modified by immunization procedures. H-Y has been proposed as the differentiation signal that causes the formation of the testes from the undifferentiated gonad in the developing embryo. This hypothesis has been explored by using a series of mice whose karyotype and phenotypic sex are paradoxical.     

H-2 Effects on cell-cell interactions in the response to single non-H-2 alloantigens

Mice expressing mutant H-2Kb alleles were tested for their ability to generate cytotoxic effector T-cells specific for the non-H-2 histocompatibility alloantigen H-4.2. Cytotoxic effectors specific for H-4.2 are preferentially restricted by the Kb allele. Mutant Kb alleles were observed to differentially regulate the magnitude of the H-4.2-specific cytotoxic effector response. Mice expressing the Kbm5, Kbm6, Kbm7, and Kbm9 alleles generated cytotoxic T-cells to the same level as mice expressing the wild-type Kb allele. Kbm8 and Kbm11 responders generated intermediate levels of effectors, whereas Kbm1, Kbm3, and Kbm10 responders did not generate detectable levels of cytotoxic effectors. Kbm4 responders produced high levels of H-4.2-specific cytotoxic effectors that were variably reactive with wild-type Kb antigens with no H-4.2. The ability to generate H-4.2-specific effectors generally correlated with (1) the ability of mutant Kb molecules to present H-4.2 to wild-type Kb-restricted effectors, and (2) the position of the respective amino acid interchanges on the Kb molecule. Mutations that altered the amino acid sequence in the vicinity of the disulfide bond in the C1 domain had the greatest deleterious effects on Kb-controlled responsiveness to H-4.2. The only exception was the Kbm11 intermediate responder, which differs from Kbm3 in both responsiveness and in a single amino acid interchange. Therefore, the amino acid sequence in the vicinity of the disulfide bond in the C1 domain plays a prominent role in determining the H-4.2-specific immune response potential. These observations are the first to clearly demonstrate association between particular MHC gene product, amino acid sequences and immune responsiveness.     

Immunodominance in the T cell response to multiple non-H-2 histocompatibility antigens. IV. Partial tissue distribution and mapping of immunodominant antigens

The immunization of C57BL/6 responder mice with spleen cells from H-2-matched BALB.B donors, which differ by multiple non-H-2 histocompatibility (H) antigens, results in the generation of cytotoxic T lymphocytes (CTL) that are specific for only a limited number of immunodominant antigens. Previous analysis of the genes encoding these dominant antigens has not mapped these genes to any of the non-H-2 H loci defined by congenic strains. It would have been expected that the histogenetic techniques employed for congenic strain selection would have preferentially identified the "strongest" H antigens. Therefore, we have investigated the possibility that immunodominant antigens do not belong to the class of non-H-2 H antigens encoded by genes mapping to H loci defined and mapped by congenic strains. The first experiments were aimed at identifying antigens that were expressed by independently derived inbred strains and were cross-reactive with the immunodominant cytotoxic T cell target (CTT-1) antigen of BALB.B. Strong cross-reaction with the C3H.SW (H-2b) strain was observed; the C3H gene encoding this antigen was mapped with BXH recombinant inbred strains. Contrary to the mapping of the CTT-1 gene to chromosome 1 in BALB.B, the C3H gene was shown to map to either chromosome 4 or chromosome 7. This result indicates that identical, or at least extensively cross-reactive, non-H-2 antigens may be encoded by genes mapping to independently segregating loci in different inbred strains. The tissue distribution of immunodominant antigens was approached by determining the reactivity of CTL specific for these antigens with either lymphoid-derived or fibroblast-derived targets. These CTL effectively lysed lymphoblast and lymphoid tumor targets but did not lyse an SV40-transformed fibroblast line that was shown to be efficiently lysed by CTL specific for non-H-2 H antigens defined by congenic strains. Therefore, it was concluded that immunodominant antigens detected by B6 anti-BALB.B CTL have a restricted tissue distribution in comparison to non-H-2 H antigens defined by congenic strains. The implications of these results for our understanding of the origin and heterogeneity of non-H-2 cell-surface antigen recognized by effector T cells are discussed.     

Antigen-induced suppression: The role of Class I major histocompatibility antigens

The role of Class I major histocompatibility (MHC) antigens in the induction of specific suppression of graft rejection has been investigated. Two experimental transplantation models have been used - fully vascularized heterotopic cardiac allografts in the mouse and fully vascularized orthotopic renal allografts in the rat. Preparations of cells expressing Class I MHC antigens, for example highly purified preparations of rat erythrocytes or platelets or mouse L cells (H2k) transfected with the D locus Class I gene of the b haplotype, LDb-1 cells, were used to pretreat recipients prior to transplantation. The function of the allograft was monitored in order to assess any beneficial effects induced by Class I MHC antigens. The results obtained implicate Class I MHC as important in the induction of specific immunosuppression of vascularized allograft rejection.     

MHC and non-MHC genes regulate elimination of lymphocytic choriomeningitis virus and antiviral cytotoxic T lymphocyte and delayed-type hypersensitivity mediating T lymphocyte activity in parallel

The course of systemic infection with lymphocytic choriomeningitis virus was studied in mouse strains differing in the MHC or non-MHC background. Virus clearance rates differed significantly between H-2 identical strains as well as between congenic strains differing in the H-2L subregion, indicating that both H-2 and non-H-2 genes may influence the elimination of this virus. Differences in virus spread prior to appearance of the immune response could not explain the observed differences in clearance rate. On the other hand, inefficient clearance always correlated with low T cell responsiveness measured in terms of virus-specific cytotoxicity and delayed-type hypersensitivity, whereas no correlation was found with regard to NK cell activity and antiviral antibody response. Analysis of F1 progeny between H-2 identical high and low responder strains showed that low responsiveness with regard to all three parameters was recessive, indicating that natural tolerance is not the mechanism explaining non-MHC dependent low responsiveness in this system. The implications of these findings are discussed with specific reference to the role of MHC genes in controlling resistance to infectious diseases.     

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)     

Murine responses to (Tyr-Glu-Ala-Gly)n: II. H-2 and non-H-2 gene effects

Mice of the H-2^b haplotype responded to the sequential polymer poly(Tyr-Glu-Ala-Gly) in the in vitro T-cell proliferative assay, irrespective of whether they were homozygous or heterozygous at the H-2^b locus. The antibody responses of the H-2^b congenic mice to this polymer were variable, with A.BY and BALB.B showing responses better than those of C57BL/6 and C57BL/10 strains. The antibody responses of the F₁ progeny of (responder × nonresponder) strains of mice to this polymer are generally lower than the responder parents. F₁ mice with C57BL/10 background were the poorest responders. Studies with F₂ mice and backcross progenies of selective breeding of high and low antibody responder (C57BL/6 × BALB/c) F₁ to high responder C57BL/6 mice indicated that both non-H-2 genes and H-2 gene dosage effects influenced the magnitude of the humoral antibody responses. Animals having low responder non-H-2 background and only half the dosage of the responder immune response genes has greatly diminished antibody responses.     

Specific prolongation of MHC class II disparate skin allografts by in vivo administration of anti-IFN-gamma monoclonal antibody

In vivo rejection of MHC class II disparate skin allografts has been thought to involve IFN-gamma-induced expression of MHC class II alloantigens because less than 3% of skin epidermal cells express MHC class II alloantigens constitutively. In our study we directly tested this hypothesis by examining the effect of in vivo administered anti-IFN-gamma mAb on rejection of MHC class II disparate skin allografts, and comparing its effect on rejection of MHC class I disparate skin allografts placed on the same individual mice. We found that anti-IFN-gamma mAb blocked the rejection of MHC class II disparate skin allografts, but had no effect on the rejection of MHC class I disparate skin allografts. These results demonstrate that endogenously produced IFN-gamma is critical for rejection of MHC class II disparate skin allografts, but not for rejection of MHC class I disparate skin allografts. Thus, this study strongly supports the concept that MHC class II rejection responses require IFN-gamma induced MHC class II expression on keratinocytes of the allograft.     

Genetic control of immune responses to the 18-kDa protein of Mycobacterium leprae. Different TH1 subsets may be involved in proliferative and delayed-type hypersensitivity responses.

In vitro and in vivo responses to the 18-kDa protein of Mycobacterium leprae have been analysed in different strains of mice. Lymphocytes from BALB/cJ (H-2d), BALB.B (H-2b), B10.BR (H-2k), and B10.M (H-2f) mice primed with 18-kDa protein yielded high T cell proliferative responses, while those from C57BL/10J (H-2b) mice yielded lower responses. Both H-2 and non-H-2 genes contributed to the magnitude of responsiveness. F1 mice from high and low responder strains showed high responsiveness to the 18-kDa protein. Supernatants from lymph node cell cultures prepared from 18-kDa protein-immunised BALB/cJ, B10.BR, and C57BL/10J mice contained IL-2 but no IL-4, indicating that activated T cells from both high and low responder mice were of a TH1 phenotype. Cell cultures from low responder C57BL/10J mice produced less IL-2 than those from high responders. The low responsiveness to the 18-kDa protein in proliferative assays might be due to a low frequency of antigen-specific T cells in the C57BL/10J mouse strain. BALB/cJ, C57BL/10J, and F1 (BALB/cJ x B10.BR) mouse strains were tested for in vivo DTH reactions to the 18-kDa protein. All strains, including C57BL/10J, were high DTH responders. Although DTH effector cells and 18-kDa protein-specific proliferative T cells belong to the TH1 subset, our data comparing high and low responder status indicate that distinct TH1 subpopulations are stimulated in response to the 18-kDa protein of M. leprae.     

Primary and secondary delayed-type hypersensitivity to minor histocompatibility antigens in the mouse.

Immunization of mice with viable allogeneic H-2-compatible spleen cells can induce a persistent state of delayed-type hypersensitivity (DTH) to these alloantigens, as measured with the footpad swelling test. Boosting of such mice, 2–4 months after priming, induced a typical secondary-type DTH reactivity. The capacity of secondary DTH to non-H-2 alloantigens could be adoptively transferred from primed mice into irradiated syngeneic hosts by means of nylon wool-nonadherent, Thy-1.2⁺ spleen cells. Vinblastine treatment of the donor mice did not affect the adoptive DTH responsiveness. These results suggest that a population of long-lived T memory cells contributes to secondary-type DTH responsiveness to non-H-2 alloantigens. The phenomenon of persistent DTH is discussed in the light of these results. The hypothesis is put forward that persistent DTH is dependent on the continuous antigen-driven differentiation of long-lived, recirculating T memory cells into nonrecirculating, functionally short-lived DTH effector cells.     

Allosensitization induced suppression of various murine tumors: role of non-H-2 antigens in antitumor immunity

Presence of alloantigens on various murine tumors was tested by tumor rejection in allosensitized Swiss mice. The results indicated the presence of alloantigen on immunogenic tumors like chemically induced fibrosarcoma (FS), ascitic sarcoma 180 (S 180) and immunogenic variant of lymphosarcoma (LS-A) in Swiss mice, while these antigens could not be detected by this procedure on spontaneous lymphosarcoma (LS). Allosensitization with skin graft was found to offer quantitatively higher antitumor resistance than the allosensitization achieved by allogeneic lymphocytes. Antitumor effect was not seen when tumor cells were inoculated earlier than day 3 of grafting. Further, host immunosuppression with whole body irradiation up to day of 3 of skin grafting abrogated the antitumor effect. H-2 compatible and non-H-2 incompatible skin graft sensitization of host could offer resistance against both S 180 and LS-A. Further, tumor immune mice rejected H-2 compatible, non-H-2 incompatible skin graft significantly earlier.     

Influence of the H-2 u haplotype on immune function in F1 hybrid mice

Recently we reported that antigen-primed T cells from (H-2 ^u × H-2 ^s)F₁ and (H-2 ^u × H-2 ^q)F₁ mice responded poorly in vitro to antigen in the context of antigen-presenting cells of the non-H-2 ^u parent. It was suggested that this effect might be due to unbalanced expression of parental antigens in the F₁ hybrid with the result that the non-H-2^u A antigens were greatly reduced or absent in these mice. If this were the case, non-H-2^u Ia-A cells might be expected to stimulate a mixed lymphocyte reaction (MLR) when cultured with Fl responder cells. When tested, (SJL × PL)F₁ responder cells reacted strongly to SJL stimulator cells. There was no significant reaction to PL stimulator cells. The use of major histocompatibility complex (MHC) congenic mice showed the stimulatory antigens to be associated with the MHC. The MLR could be blocked significantly by monoclonal A-specific antibody of the appropriate specificity. When a monoclonal antibody reactivewith a private epitope associated with A^s was used to probe for the presence of A^s on the surface of (SJL × PL)F₁ spleen cells, no antigen could be detected, indicating loss or alteration of this antigen. These findings suggest that an alteration of the expression of the parental A^s molecule may be responsible for this phenomenon.Abbreviations used in this paper APC antigen-presenting cells - BSS balanced salt solution - CTL cytotoxic T lymphocyte - IL-2 interleukin-2 - MHC major histocompatibility complex - MLR mixed lymphocyte reaction - T₂ suppressor T lymphocyte     

Rejection of skin allografts by CD4+ T cells is antigen-specific and requires expression of target alloantigen on Ia- epidermal cells

The effector mechanism of skin allograft rejection has been characterized as Ag specific, rejecting cells that express the target alloantigen but sparing those that do not. However, the rejection of MHC class II disparate skin grafts, in which very few cells (Langerhans cells) actually express the target Ia Ag could conceivably proceed by either one of two distinct rejection mechanisms. One possibility is that Ia- cells are destroyed by a sequence of events in which CD4+ T cells, activated by Ia+ LC, elaborate soluble factors that are either directly cytolytic or that recruit and activate non-specific effector cells. The alternative possibility is that activated CD4+ T cells elaborate soluble factors which induce Ia expression on Ia- cell populations, and that these Ia+ cells are subsequently destroyed by effector cells specific for the induced Ia alloantigens. We found that rejection of Ia+ LC was not of itself sufficient to cause rejection of skin grafts, indicating that skin allograft rejection is contingent on the destruction not only of LC but of other graft cell populations as well. We then investigated whether CD4+ T cells rejected allogeneic skin grafts in an antigen specific fashion. To do so, we engrafted immunoincompetent H-2b nude mice with trunk skin grafts from B6----A/J allophenic mice because such skin is composed of mutually exclusive cell populations expressing either H-2a or H-2b histocompatibility Ag, but not both. The engrafted mice were subsequently reconstituted with H-2b CD4+ T cells. The CD4+ T cells destroyed keratinocytes of A/J origin but spared keratinocytes of B6 origin, even though neither cell population constitutively expresses target IAk alloantigen. The targeted rejection of A/J keratinocytes but not of B6 keratinocytes indicates that the target Ia alloantigen must have been induced on Ia- A/J keratinocytes, rendering them susceptible to destruction by anti-Iak-specific CD4+ effector cells. These data demonstrate that CD4+ T cell rejection of skin allografts is mediated by Ag-specific CD4+ cytolytic T cells and hence, requires the induction of target Ia alloantigens on epidermal cells within the graft.     

Alloreactive T cell responses and acute rejection of single class II MHC-disparate heart allografts are under strict regulation by CD4+ CD25+ T cells

Skin but not vascularized cardiac allografts from B6.H-2bm12 mice are acutely rejected by C57BL/6 recipients in response to the single class II MHC disparity. The underlying mechanisms preventing acute rejection of B6.H-2bm12 heart allografts by C57BL/6 recipients were investigated. B6.H-2bm12 heart allografts induced low levels of alloreactive effector T cell priming in C57BL/6 recipients, and this priming was accompanied by low-level cellular infiltration into the allograft that quickly resolved. Recipients with long-term-surviving heart allografts were unable to reject B6.H-2bm12 skin allografts, suggesting potential down-regulatory mechanisms induced by the cardiac allografts. Depletion of CD25+ cells from C57BL/6 recipients resulted in 15-fold increases in alloreactive T cell priming and in acute rejection of B6.H-2bm12 heart grafts. Similarly, reconstitution of B6.Rag(-/-) recipients with wild-type C57BL/6 splenocytes resulted in acute rejection of B6.H-2bm12 heart grafts only if CD25+ cells were depleted. These results indicate that acute rejection of single class II MHC-disparate B6.H-2bm12 heart allografts by C57BL/6 recipients is inhibited by the emergence of CD25+ regulatory cells that restrict the clonal expansion of alloreactive T cells.     

In vivo priming of mouse CTL precursors directed to product of a newly defined minor H-42 locus is under a novel control of class II MHC gene

In a previous study, we discovered a new mouse minor histocompatibility antigen encoded by a locus at 8.5 cM apart from the H-2 complex, and we have since named the locus H-42. One allele of H-42, which is named H-42a, had been elucidated, but the other alleles, which we tentatively named H-42b, have not been elucidated. In the present study, we explored MHC control on the anti-H-42a cytotoxic T lymphocyte (CTL) responsiveness in H-42b mice. In vivo immunization (i.v. injection) of H-42b mice with 5 to 30 X 10(6) spleen cells (SC) bearing allogeneic H-42a antigen but carrying H-2 complex (mouse MHC) matched with the H-42b mice failed to prime anti-H-42a CTL but induced stable and specific anti-H-42a CTL unresponsiveness, i.e., tolerance, in the H-42b recipient mice. In contrast, H-2 heterozygous H-42b F1 mice injected with SC bearing H-42a alloantigen on either of the parental H-2 haplotypes were effectively primed to generate anti-H-42a CTL. Exploration of the region or subregion in the H-2 complex of H-42a donor SC that should be compatible with H-42b recipient mice for the induction of their anti-H-42a CTL tolerance demonstrated that the compatibility at I region, most probably I-A subregion, but not at K, S, or D region, determined the induction of the tolerance. MHC class II compatible H-42a skin graft (SG) to H-42b mice, however, consistently primed the anti-H-42a CTL in the H-42b recipients. These results were discussed in several aspects, including uniqueness of MHC class II control on the CTL response to minor H-42a antigen, possibility of inactivation of responding anti-H-42a precursor CTL or helper T cells in H-42b mice by encountering the veto cells present in MHC class II-matched H-42a SC population, and significance of the present observations as a mechanism of CTL tolerance to self-components.     

MHC alloantigens elicit secondary,but not primary,indirect in vitro proliferative responses

The relative contributions of direct and indirect pathways of allorecognition to graft rejection remain controversial. Recent reports suggest that the indirect pathway may play a prominent role in both acute and chronic allograft rejection. Such studies suggest that MHC-derived allopeptides are more immunogenic than those derived from minor histocompatibility or other nominal Ags. The aim of this study was to characterize the immunogenicity of MHC alloantigens in MHC-defined miniature swine via primary and secondary MLR culture assays. APCs were selectively depleted from either responder or stimulator cell populations to specifically analyze direct and indirect proliferative responses, respectively. Radio-resistant cytokine secretion and subsequent backstimulation of responder cells was eliminated by using stimulators that were either lysed or unresponsive to the responder MHC haplotypes. When the effect of backstimulation was eliminated from MLR culture assays, indirect proliferative responses were not observed among naive responders. Only after in vivo priming of responder animals could indirect proliferation be detected. These data do not refute the potential importance of indirect allorecognition in graft rejection. However, they suggest that MHC-derived alloantigens behave similarly in vitro to minor histocompatibility Ags, with comparable immunogenicity. These data also suggest that the MLR culture assay does not accurately reflect the importance of indirect mechanisms that have previously been reported in experimental models of graft rejection. A greater understanding of the indirect pathway and the associated immunogenicity of MHC allopeptides has the potential benefit of enabling the development of therapeutic interventions to prevent or halt allograft rejection.     

Two distinct high immune response phenotypes are both controlled by H-2 genes mapping K or I-A

Murine responses to immunization with 2, 4, 6-trinitrophenyl (TNP) conjugated to autogenous mouse serum albumin (MSA) in complete Freund's adjuvant (CFA) are controlled by a gene(s) in the K or I-A region of H-2 complex. High immune responses of both H-2d and H-2b mice have been mapped to this region of the major histocompatibility complex. No modifying effects were observed from genes to the right of I-A in either responder haplotype. High responsiveness controlled by Kb or I-Ab is inherited with complete or partial recessivity, depending on the route of immunization and the sex of the responder. However, high responsiveness controlled by Kd or I-Ad is inherited dominantly. This unusual pattern of inheritance of immune responsiveness to TNP-MSA is consistent with the genetic mapping to K or I-A. TNP-MSA-specific T-cell reactivity following immunization with TNP-MSA in vivo was examined utilizing a T-cell-dependent proliferation assay in vitro with cells obtained from high or low responder mice. Genetic mapping and mode of inheritance in this assay for antigen-specific T-cell reactivity corresponded with results obtained from a plaque-forming cell (PFC) assay measuring antibody production by B cells. Both the proliferative and PFC responses are probably under the same Ir gene control. Both gene dosage effects and Ir-gene-product interaction could influence the generation of specific immune responsiveness in F1 hybrids between high and low responders to TNP-MSA.