Murine antigen H-2.7: localization of its antigenic determinant to the Ss (C4) molecule

Murine sex-limited protein (Slp) antigenic sites in human complement component C4

Human complement component C4 is encoded by two HLA-linked loci, A and B. In the mouse, the H-2 region contains structural genes for two serum proteins that react with antibodies to human C4, but one of these proteins (Slp) has no C4 hemolytic activity. Because the product of C4-A locus in man has low hemolytic activity, a previous report suggests it may be the homologue of murine Slp. We show here that Slp antigenic determinants are found in human C4. However, they are expressed in the products of both loci A and B, that is, C4A and C4B, since both proteins were specifically immunoprecipitated by the IgG fraction of alloantisera to mouse Slp. Therefore, Slp-associated structural features are preserved in evolution, although they do not seem to be relevant to the hemolytic properties of C4.

The traditional and a new version of the mouse H-2 complex

The H-2 complex has traditionally been interpreted as a maze of regions, subregions and loci coding for different traits. The two main theses presented here are, first, that a single H-2 locus is pleiomorphic in that it controls several functions such as allograft rejection, cell-mediated lymphocytotoxicity, mixed lymphocyte reaction, immune response, immune suppression and restriction of T-cell specificity; and second, that the physiological function of the H-2 complex is to guide T lymphocytes in their function of distinguishing self from non-self, and that all other H-2-controlled traits are artificial derivatives of this basic function. These two theses lead to a new, simplified interpretation of the H-2 complex.