An alloantiserum produced in the mouse has been used to detect an antigen which is present only in male serum from certain inbred strains of mice, e.g., DBA/2J, A/J, and BALB/e. Genetic tests reveal that the presence of this antigen is controlled by a dominant autosomal gene which is expressed only in males of the proper genotype. Test crosses and analysis of congenie resistant strains indicate close linkage between the sex-limited protein (Slp) and the histocompatibility-2 (H-2) region of linkage group IX. Analysis of seven intra-H-2 recombinant strains is consistent with the placement of the genetic determinant for Slp within the H-2 region in the same position as the Ss (serum substance) determinant. Immunological evidence suggests that the Slp antigenic sites reflect structural variation in the Ss component of mouse serum.

SummaryThe immunodominant CD4 T cell epitope of the bacteriophage k cI repressor protein in several inbred mouse strains can be represented by a peptide encompassing amino acids 12-26. Here, we show that this peptide, and a variety of its sequence variants, can induce immediate-type hypersensitivity in mice. 12-26 variants that differ by as little as single amino acid residues deviate greatly in their ability to induce hypersensitivity. Further, differences in major histocompatibility complex class II alleles appear to be as influential as changes in peptide structure in determining whether hypersensitivity is developed. The ability of a given peptide-class II combination to induce hypersensitivity correlates with production of peptide-specific antibody, but not with ability or inability to induce a T cell proliferative response. Administration of anti-interleukin 4 (IL-4) mAb prevents the development of hypersensitivity, and analysis of cytokine production by T cell hybridomas derived from peptide-immunized mice suggests that whether a given peptide-class II combination can induce hypersensitivity depends on its ability to induce IL-4 production. The data demonstrate that changes in the nature of the epitope(s) recognized by the CD4 T cell population can result in qualitative differences in the response elicited in this population, ultimately leading to dramatic quantitative and qualitative variations in the effector phase of the immune response.T he ligand for most CD4 TCRs of the od/3 type is a complex of a class II MHC molecule and a peptide subfragment of a protein antigen. This ligand is created on the surface of an APC via internalization of the antigen, its degradation to peptide fragments, and association of some of these fragments with class II molecules via agretypic determinants on the peptides (1). Linear peptides of 5-20 amino acids bearing agretypic and T cell epitypic determinants can substitute for intact antigen in in vitro T cell activation assays (2-4). These findings have been exploited towards the development of synthetic peptide vaccines (5, 6), and the design of peptides that can block autoimmune T cell responses in vivo (7,8).Linear synthetic peptides are much simpler in structure than the high molecular weight protein antigens normally used to elicit immune responses. In addition, synthetic peptide chemistry allows facile generation of an assortment of different mutant forms of any given peptide. Thus, changes in putative epitypic and agretypic determinants in a peptide can easily be made and assayed for their effect on immunogenicity in vitro and in vivo. Studies from a number of laboratories have demonstrated the utility of this approach towards the elucidation of the structural correlates of T cell immunogenicity (9-11). Such studies have shown that changes in the primary structure of synthetic peptides often result in alterations in their immunogenicity that are not easily explained by our current understanding of the nature of agretypic and epitypic determinants (12)(13)(14).While ...

The Eb gene of the mouse contains a recombinational hotspot which plays a predominant role in meiotic crossing-over within the I region of the mouse major histocompatibility complex (MHC). The nucleotide sequences of five recombinants derived from H-2k/H-2b heterozygotes at the Eb locus placed the sites of recombination in each recombinant haplotype within a 2.9 kilobase (kb) segment located fully within the second intron of the Eb gene. Further resolution of the crossover sites was not possible since the nucleotide sequences of the parental and recombinant haplotypes are identical within this segment. The molecular characterization of these five recombinants considered in conjunction with three previously reported intra-Eb recombinants indicates that there are at least two distinct sites of recombination within the Eb recombinational hotspot. In a related study, an examination of the nucleotide sequence of the H-2p allele of the Eb gene revealed a major genetic rearrangement in the 5' half of the intron in this haplotype. A 597 base pair (bp) nucleotide sequence found in the H-2p haplotype is replaced by a 1634 bp segment found in the H-2b and H-2k haplotypes. Sequence analysis of this 1634 bp segment shows strong nucleotide sequence similarity to retroposon long terminal repeat (LTR), env, and pol genes indicating that this segment of the second intron has evolved through retroposon insertion. The location of these retroposon sequences within the 2.9 kb recombination segment defined by the five H-2k/H-2b recombinant haplotypes suggests a possible relationship between these retroviral elements and site-specific recombination within the second intron of the Eb gene.

The rough coat (rc) is a spontaneous recessive mutation in mice. To identify the mutated gene, we have characterized the rc phenotype and initiated linkage mapping. The rc mice show growth retardation, cyclic and progressive hair loss, hyperplastic epidermis, abnormal hair follicles, cardiac muscle degeneration, and reduced amount of collagen and elastin in the skin and heart. The rc locus was mapped at 32.0 cM on chromosome 9, close to the loxl gene. Lysyl oxidase-like (LOXL) protein is a novel copper-containing amine oxidase that is required for the cross-linking of elastin and collagen in vitro. LOXL is expressed at high levels in the skin and heart, where the rc mice show strong phenotype. The expression pattern and the genetic proximity to rc suggested loxl as a potential candidate gene. In rc mice, the loxl mRNA was reduced in the skin and the LOXL protein in the heart, dermis, atrophic hair follicles, and sebaceous glands. No mutations, however, were identified within the coding region of loxl, and offspring from rc/rc and loxl null mice crossing were phenotypically normal. Based on these results, loxl appears non-allelic to rc. Heart- and skin-specific downregulation of LOXL in rc mice, however, may contribute to the extracellular matrix alterations and the rc phenotype.

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