Uneven tissue distribution of minor histocompatibility proteins versus peptides is caused by MHC expression.

Naturally processed minor histocompatibility (H) peptides corresponding to H-4b, H-Y, and an unmapped BALB.B minor H gene were quantified in a relative way in 15 different tissues of male BALB.B mice. For one of these minor H antigens, we could also determine the relative content of the respective protein. For each minor H peptide, an individual tissue distribution was found. Tissues expressing little or no MHC (major histocompatibility complex), like brain, contained only small amounts of minor H peptides or none at all, although the same tissues contained minor H protein in substantial quantities. By contrast, Kb-expressing brains from mice transgenic for Kb under control of the glial acidic protein promoter contained both minor H peptide and protein in high amounts. Thus, the expression of minor H peptides in a given tissue is dependent on coexpression of the restricting MHC class I molecules.