How polymorphic are class II loci of the mouse H-2 complex?

Polymorphism and estimation of the number of MhcCyca class I and class II genes in laboratory strains of the common carp (Cyprinus carpio L.)

Restriction fragment length polymorphisms (RFLPs) have been identified in the Mhc of the carp (MhcCyca) using class I (Cyca-Z) and class II (Cyca-YB) specific probes. The K1-5 and K2-1 probes were obtained as PCR products after amplification of genomic DNA from a European carp using primers deduced from genomic sequences, and were shown to be 90% and 80% similar to Cyca-Z exon 3 and Cyca-YB exon 2 sequences, respectively. Six carp strains of different geographical origins and genomic status were studied. In homozygous gynogenetic carp strains the class I probe K1-5 hybridized to 9-12 fragments, whereas the class II probe K2-1 hybridized to 3-5 fragments. Thus, the Cyca consists of multiple class I and class II genes. The level of polymorphism of the Cyca genes of the strains studied was calculated as the percentage of polymorphic fragments among the total number of fragments observed, and was shown to be 70% for class I and 40-66% for class II genes. In addition, a possible correlation was investigated between a serologically defined locus K, which was demonstrated previously to incorporate class I-like characteristics, and molecular genotyping using the class I probe. Two gynogenetic families, which were serologically typed K1 and K2 homozygous, also differed in their RFLPs using a class I probe. This would suggest that the K locus is part of the Cyca complex.

Determinants of the B-cell response against a transgenic autoantigen

The failure to induce self-tolerance of simian virus 40 large tumor antigen (T antigen) expressed in the pancreatic beta cells of transgenic mice results in an autoimmune response against this protein and the cells that synthesize it. In every transgenic mouse with delayed onset of T-antigen expression and consequent nontolerance, B cells, T cells, and macrophages are attracted to and infiltrate the pancreatic islets. In contrast, the incidence, onset, and intensity of the B-cell response to produce anti-T-antigen autoantibodies vary considerably with genetic background. Thus the initial attraction of lymphocytes to the cells synthesizing a non-self antigen can be separated from the activation of a B-cell response against it. Haplotypes of the major histocompatibility complex (MHC) differentially influence the character of the autoimmune response, with H-2d and H-2k conferring a high incidence of humoral autoimmunity. Additional non-MHC linked genes are also implicated in control of the B-cell response.

New evidence for trans-species evolution of the H-2 class I polymorphism

A serological survey using alloantisera specific for the H-2 class I antigens in Japanese wild mice. Mus musculus molossinus, revealed a high frequency of the H-2Kf antigen. This antigen has also been found in European wild mice, M. m. domesticus and M. m. musculus. In this survey, the H-2Kf antigen was characterized through the use of ten newly isolated monoclonal antibodies raised against cells of a Japanese wild mouse, and by Southern blot analysis using an H-2K locus-specific probe which hybridizes with the 3' end of the gene. The serologically identified H-2Kf antigens revealed several minor variations in reactivities to the monoclonal antibodies. However, all the antigens examined could be clearly separated into two types with respect to the restriction fragment length polymorphism (RFLP) pattern. The first type, found together with a single, characteristic RFLP pattern, was always associated with the presence of reactivity to one particular monoclonal antibody MS54. The second type, found to represent different RFLP patterns, is associated with the absence of reactivity to MS54. This concordance between the presence of an antigenic determinant and a particular RFLP was observed not only within Mus musculus subspecies but also in a different species: M. spretus, carrying the same antigenic determinant, gave an identical RFLP to that of the other MS54-positive Mus musculus subspecies. The data suggest that the antigenic determinant specific for MS54 is an ancient polymorphic structure which has survived the long period of diversification of Mus species (approximately 2-3 million years) without alteration, and is associated with a stable DNA structure at the 3' end of the H-2K gene.

Genetic characterization of FLA, the cat major histocompatibility complex

The major histocompatibility complex (MHC) of the domestic cat (termed FLA) has been refractile to genetic and serological definition largely because of repeated failure to detect cytotoxic antibodies in multiparous cats or to elicit antibody following allogeneic lymphocyte immunization. We have developed a protocol for producing cytotoxic alloantisera in the cat following rejection of multiple surgical skin grafts. Of 59 cats subjected to grafting, 13 produced lymphocytotoxic antisera which had varying specificities among a panel of outbred cat cells. A population cluster analysis of the 13 alloantisera permitted the identification of six clusters of overlapping FLA specificities. Serological analysis of cells from 12 cat kindreds led to the definition of 24 allogeneic haplotypes, which segregate as a single Mendelian complex. Feline FLA antisera were characterized as class I or class II specific by immunoprecipitation of FLA gene products on lymphocyte cell surfaces. Abundant antigenic polymorphisms for both class I and class II MHC determinants were discovered, a result consistent with precedence in other species and the common expectation of the adaptive value of MHC variation. Development of feline MHC typing reagents and the definition of haplotypes for the cat hold promise for experimental analysis of valuable feline models for virus-induced immune deficiencies.

Characterization of the MHC class II region in cattle. The number of DQ genes varies between haplotypes

The organization of the major histocompatibility complex (MHC) class II region in cattle was investigated by Southern blot analysis using human probes corresponding to DO, DP, DQ, and DR genes. Exon-specific probes were also employed to facilitate the assessment of the number of different bovine class II genes. The results indicated the presence of single DO beta and DR alpha genes, at least three DR beta genes, while the number of DQ genes was found to vary between MHC haplotypes. Four DQ haplotypes, DQ alpha 1 beta 1 to DQ alpha 2 beta 4, possessed a single DQ alpha and a single DQ beta gene whereas both these genes were duplicated in eight other haplotypes, DQ alpha 3 beta 5 to DQ alpha 9 beta 12. No firm evidence for the presence of bovine DP genes was obtained. The same human probes were also used to investigate the genetic polymorphism of bovine class II genes. DQ alpha, DQ beta, DR alpha, DR beta, and DO beta restriction fragment length polymorphisms (RFLPs) were resolved and in particular the DQ restriction fragment patterns were highly polymorphic. Comparison of the present result with the current knowledge of the class II region in other mammalian species suggested that the DO, DP, DQ, DR, and DZ subdivision of the class II region was established already in the ancestor of mammals. The DP genes appear to be the least conserved class II genes among mammalian species and may have been lost in cattle. The degree of polymorphism of different class II genes, as revealed by RFLP analyses, shows striking similarities between species.

Polymorphism and mapping of the class II genes in the rat: RT1.B, RT1.D, and RT1.H, a new DP-like region

The major histocompatibility complex of the rat (RT1) encodes the class II molecules involved with antigen presentation and cell to cell communication. The organization of these class II genes has been studied by Southern blot hybridization using genomic DNA from inbred and recombinant rat strains digested with various restriction endonuclease and hybridized under stringent conditions with probes for mouse class II and human class II genes. Analysis of the restriction fragment length polymorphisms has mapped the class II genes relative to each other. We have confirmed the order of the alpha- and beta-chain genes in the RT1.B region, mapped the RT1.D region relative to RT1.B and showed that it has alpha- and beta-chain loci, and identified a new HLA-DP-like locus, RT1.H, to the RT1.A side of RT1.B. The RT1.H alpha and RT1.H beta genes map to the region around the recombination point in R22, and there appears to be a hot spot of recombination in RT1.H. The H beta and D beta genes have high levels of polymorphism; B beta, B alpha, and H alpha have intermediate levels of polymorphism, and D alpha has a low level of polymorphism.

DNA polymorphism of MHC III genes in inbred and wild mouse strains

Genes encoding the second component (C2), factor B, and complement protein C4 and Slp (sex-limited protein) are members of the major histocompatibility complex class III gene cluster. In this report we describe isolation of a mouse C2 cDNA clone and its use together with factor B and C4 cDNA clones to examine the S region in a panel of 42 haplotypes in laboratory and wild mice representing 5 species and subspecies of Mus. Conservation of the C2 factor B gene duplex was evidenced by relatively limited polymorphism associated with speciation and nucleotide sequence homology between mouse and human C2 and factor B. The C4-Slp gene duplex, on the other hand, showed extensive polymorphism by DNA blot analysis. This polymorphism correlated poorly with the C2/factor B restriction fragment length polymorphism, suggesting independent evolution of these two segments of the S region. Taken together, these data will be of particular importance in studies of mouse strains with abnormal regulation of immune effector systems since the class III gene products are essential for activation of the complement cascade.

Two forms of the Ia antigen-associated invariant chain result from alternative initiations at two in-phase AUGs

The Ia antigen-associated invariant chain (In) exists in humans as two major related forms, p33 and p35. The mRNA for In contains two in-phase AUGs, at positions 8 and 56 from the cap site. Cells transfected with a full-length cDNA clone in an expression vector synthesize both p33 and p35. Cell-free translation of mRNA synthesized in vitro from cDNA also produces both forms. When the first ATG is deleted from the cDNA clone, only the smallest form of In is produced. Mutations introduced at the second ATG lead to synthesis of the large form only. The alternative use of two in-phase AUGs on a unique mRNA is thus responsible for the synthesis of p33 and p35. This is the first documented example of such a mechanism in nonviral systems.

Unexpected expression of a unique mixed-isotype class II MHC molecule by transfected L-cells

Class II (Ia) major histocompatibility complex (MHC) molecules are heterodimeric integral membrane proteins composed of non-covalently linked alpha and beta glycoprotein chains. Studies of both normal cells and L-cell transfectants have shown that neither alpha- nor beta-chains are found on the cell surface alone, and that alpha beta dimers are required for membrane expression. In both mouse and man, several distinct non-allelic alpha and beta genes exist. Analysis of Ia molecules by immunoprecipitation and two-dimensional gel electrophoresis has demonstrated apparently selective association of particular pairs of the various alpha- and beta-chains to form the expressed class II isotypes I-A and I-E (mouse) or DQ, DP and DR (human). Because the various alpha- or beta-chains encoded by distinct loci exist in many allelic forms within a species, such specific pairing suggests a special role for isotypically conserved regions of each chain in the association process. In attempting to localize such putative assembly-controlling regions using the technique of DNA-mediated gene transfer, various combinations of murine alpha and beta genes were introduced into L-cells. Here we report the unexpected observation, following transfection, of mixed-isotype (Ad beta Ea/k alpha) molecules on the L-cell membrane and document that the formation of this pair is strongly influenced by allelic polymorphism of the A beta chain.