Identification of a fourth class of proteins linked to the murine major histocompatibility complex.

A series of proteins biochemically and genetically distinct from previously defined murine major histocompatibility complex class I and class II antigens is precipitated by a congeneic anti-H-2d antiserum. Sixteen such proteins have been defined, exhibiting a range of molecular weights (approximately 15,000-30,000) and isoelectric points (pI approximately 4-9). These proteins are not glycosylated, and they are probably not expressed at the cell surface. They are expressed most strongly in normal macrophages and macrophage cell lines and are also found in fibroblasts, B, T, and null cell lines. The genes controlling the expression of these proteins have been tentatively mapped within the H-2 complex, between the K and I-A subregions. Three alleles have been defined: mice of the H-2 haplotypes b and q possess a "null" allele, i.e., do not express any demonstrable protein product. Mice of the d haplotype cane be distinguished by their two-dimensional gel pattern from mice of all other positive H-2 types tested thus far (a, k, f, s, and ja).