A third class I major histocompatibility complex antigen encoded by a gene in the D region of the H-2 d haplotype recognized by cytotoxic T lymphocytes

The D region of the H-2 ^d haplotype contains five class I genes: H-2D ^d , D2 ^d , D3 ^d , D4 ^d and H-2L ^d . Although previous studies have suggested the presence of D-end encoded class I molecules in addition to H-2D^d and H-2L^d, segregation of genes encoding such molecules has not been demonstrated. In this report we have used cãtotoxic T lymphocytes (CTL) to examine the D region of the H-2 ^d haplotype for the presence of additional class I molecules. CTL generated in (C3H × B6.K1)F₁ (K ^k D ^k , K ^b D ^b ) mice against the hybrid class I gene product Q10^d/L^d expressed on L cells cross-react with H-2L^d but not H-2D^d molecules, as determined by lysis of transfected cells expressing H-2L^d but not H-2D^d. Although H-2L^d-specific monoclonal antibodies (mAb) completely inhibit H-2L^d-specific CTL from killing B10.A(3R) (K ^b D ^d L ^d ) target cells, only partial inhibition of anti-Q10 CTL-mediated lysis was observed, suggesting the presence of an additional D-end molecule as a target for these latter CTL. To identify the region containing the gene encoding the Q10 cross-reactive molecule, we show that anti-Q10 CTL lyse target cells from a D-region recombinant strain B10.RQDB, which has H-2D ^d , D2 ^d , D3 ^d , D4 ^d , and H-2D ^b but not the H-2L ^d H-2 ^d , and H-2L ^d (including D2 ^d , D3 ^d , and D4 ^d , lacks this anti-Q10 CTL target molecule. Together, these data demonstrate that a class I gene mapping between H-2D ^d and H-2L ^d encodes an antigen recognozed by anti-Q10 CTL. A likely candidate for this gene is D2 ^d , D3 ^d or D4 ^d .     

Antigen-specific helper T cells recognize determinants encoded in the H-2D region of the H-2 gene complex

Observations have frequently been interpreted as showing that the helper T cells which collaborate with alloantigen-specific cytotoxic T-cell precursors can only recognize antigens encoded in the I region of the H-2 gene complex. An experimental system is described here that allows analysis of the recognition repertoire of these helper cells. CBA helper T-cell precursors can be primed in vitro to antigens encoded in the H-2 ^b gene complex. These helpers can then be tested for the existence of a subset of helper cells which recognize antigens encoded in the D region of H-2 ^b haplotype. CBA thymocytes were used as a source of cytotoxic T-cell precursors that respond poorly in the absence of exogeneous helper activity. The source of alloantigen was varied by using irradiated spleen cells from various (BALB/c × recombinant)F₁ hybrid mice as stimulator cells. When the stimulator cell bears BALB/c determinants recognized by the cytotoxic T-cell precursor and also bears only the D region antigens of the H-2 ^b haplotype, an anti-BALB/c cytotoxic response is generated only if the anti-H-2^b helper population contains cells able to recognize H-2D^b. A positive cytotoxic response was obtained, indicating that helper cells are not limited to recognition of I region antigens and can efficiently recognize antigens encoded in the D region of the H-2 gene complex. This was confirmed by the demonstration of helpers specific for H-2D^d. We were unable to detect any evidence for Ia-restricted recognition of the H-2D alloantigens, suggesting that, as for cytotoxic T lymphocytes (CTL), helper cell recognition of class I alloantigens is an unrestricted event.     

Family organization of mouse H-2 class I genes

The H-2 complex of the mouse contains numerous class I genes of unknown function. These genes are here classified into families according to homology in the exons encoding the variable domains. There are one major and at least five minor families, whose members are partly clustered and partly interspersed on the mouse chromosome. DNA sequences show that not only Tla and Qa-2 but also other minor-family genes have intact coding domains. These may be expressible genes of novel types.     

A bovine class I major histocompatibility complex molecule plus a Theileria parva antigen resembles mouse H-2Kd

Two BoT2+, BoT8+ cytotoxic T cell clones were generated from peripheral blood of a steer immunized with the intracellular protozoan parasite Theileria parva. Both cytotoxic T cell clones appeared to be restricted by the same major histocompatibility complex (MHC) molecule and were specific for the immunizing parasite clone. However, one of the two clones also recognized uninfected mouse cell lines carrying the H-2d haplotype. Inhibition of cytotoxicity with monoclonal antibodies specific for polymorphic determinants on H-2 molecules confirmed that this CTL clone recognized the H-2Kd MHC molecule. These results extend to the bovine system observations in other species that foreign MHC mimics self MHC plus antigen.     

Organization and structure of the Qa genes of the major histocompatibility complex of the C3H mouse: implications for Qa function and class I evolution.

We have determined the structure and organization of the entire Qa family of class I genes from the major histocompatibility complex of the C3H mouse. Restriction maps of overlapping lambda and cosmid clones reveal that there are only five Qak genes: Q1k, Q2k, Q4k, Q10k and a Q5/9 hybrid, presumably generated by unequal homologous recombination. The resulting deletion of Q6-Q9 is consistent with the Qa-2null phenotype of this mouse strain. We have sequenced the Qak genes, and predict that each may encode a class I molecule with a structure comparable with that proposed for the transplantation antigens. Furthermore, these Qa products should be able to bind peptides and interact with appropriate T-cell receptors. Interestingly, in comparing Qak and H-2k sequences, we find limited evidence of interlocus gene conversion between Qa and H-2 loci, suggesting that the Qa genes are not likely to serve as a reservoir of genetic information for the generation of H-2 diversity within this haplotype.     

Teratocarcinoma transplantation antigens are encoded in the H-2 region

Evidence is presented for the existence of teratocarcinoma transplantation antigens (Gt) encoded within the H-2 complex and present also on adult tissues. It has not been possible to separate these Gt loci from H-2 by recombination, and Gt factors map to each end of the H-2 complex. Previous reports indicating separation of all Gt loci from H-2 are reinterpreted. One class of such apparent recombinants has been shown to result from the outgrowth of tumor variants in mice of resistant genotype.Aspects of this work were presented at the 10th Cold Spring Harbor Conference on Cell Proliferation, September 1982.     

Genomic analysis of the H-2 complex region associated with mouse t Haplotypes

Naturally occurring t haplotypes suppress recombination over a region of mouse chromosome 17 that includes the H-2 complex. Each of these t haplotypes is associated with a specific set of H-2 alleles and can be placed into one of a limited number of complementation groups. Genetic studies have demonstrated the existence of a basic homology in genomic organization among all t haplotypes. We used an H-2 cDNA probe to investigate, at the molecular level, possible relationships among the H-2 regions of different t haplotypes. We identified a family of t haplotype-specific restriction fragments that carry DNA sequences homologous to the H-2-like genes. Surprisingly, the H-2-defined restriction patterns from all five complete t haplotypes analyzed are highly homologous, even though H-2 gene products expressed are antigenically distinct. These data lead to two major conclusions. First, all t haplotypes were derived from a small number of closely related ancestors. Second, the H-2 complex region associated with each primordial t chromosome has been maintained within at least the five present-day t haplotypes analyzed here. Hence the H-2 complex is an integral component of naturally occurring t haplotypes.     

H-2 class I antigen expression on mouse teratocarcinoma cell lines

Immunity against PCC3 teratocarcinoma cells (129, H-2 ^b) was induced in allogeneic (C3H, H-2 ^k) mice by preimmunization with L cells (C3H, H-2 ^k) expressing cosmid-introduced K ^b or D ^b genes, but not with nontransfected L cells. In addition, the growth of PCC3 cells in sublethally irradiated (C3H × B6-H-2 ^bm1)F₁ and (C3H × B6-H-2 ^bm13 )F₁ mice bearing the K ^bm1 and D ^bm13 mutations, respectively, was either prevented, stopped, or delayed in comparison with the (C3H × B6)F₁ (k × b) mice, which failed to reject the PCC3 cells. The teratocarcinoma line OC15S was exceptional because it reacted specifically with K^b- and D^b-specific (but not I^b-specific) alloantisera, and because K^b- and D^b-specific antibodies could be absorbed by OC15S cells. The subpopulation of OC15S cells bearing the ECMA-7 antigen characteristic for embryonic carcinoma (EC) cells was isolated by the fluorescence-activated cell sorter and was shown to react specifically with K^b- and D^b-specific antisera. These experiments show that teratocarcinoma cells express antigens similar or identical to the K-and D-region products of differentiated cells. The lack of expression of class I antigens is thus neither a condition nor a consequence of the pluripotentiality of the EC cells. The exact nature of the major histocompatibility complex antigens on EC cells has yet to be established using the methods of molecular biology and biochemistry.     

A histocompatibility region (H-2IC) in theIC region of theH-2 complex of the mouse

Skin graft rejection in congenic pairs of mice differing only at theH-2 complex appears to be influenced by at least 3 genes (H-2K, H-2D, H-2I); we now describe a fourth,H- 2IC: Grafts transplanted across anIC difference are sometimes rejected. TheI-C regions of three differentH-2 haplotypes (d,k,s) were studied in different combinations, and variable patterns emerged: (a)IC ^d : B10.S(7R) show delayed or no rejection of first B10.S(9R) grafts, but grafts to immunized recipients were usually rejected in 20 days; (b)IC ^k : in two combinations (A.AL A and B10.HTT B10.S[9R]) first grafts were rejected by day 30, although grafts to immunized mice showed a different pattern. In the third combination (B10.HTTB10.S[7R]) first grafts were retained but immunized mice rejected their grafts, (c)IC ^s : B10.S(9R) regularly reject B10.S(7R) first grafts, but immunized mice retain their grafts. In two other combinations first grafts were retained but grafts to immunized recipients were rejected; while in a third combination rejection did not occur at all. The background of the recipient appeared to be important in determining the variable pattern of rejection, and there is evidence for a similarity of the H-genes inIC ^s andIC ^k , and inIC ^k andIC ^p . Graft rejection occurred independently of known differences in Ia specificities, indicating thatH-2IC and the genes determining Ia specificities are probably different, although when grafts were performed in the presence of known la differences, graft rejection usually occurred.