The major histocompatibility complex (Mhc) is a group of loci coding for lymphocyte membrane glycoproteins that provide the context for the recognition of foreign antigens in the initial phase of the immune response. The complex contains a large number of loci, some of which are highly polymorphic. The complexity and polymorphism pose a number of questions concerning the evolution of the Mhc. In an attempt to answer some of these questions, we have begun to study the Mhc of the mole-rat, Spalax ehrenbergi, a rodent representing a complex of sibling species occupying ecologically and geographically clearly delineated regions within the borders of Israel. In an earlier publication we identified the Spalax major histocompatibility (Smh) complex serologically and biochemically. Here, we analyze the Smh by Southern blotting of DNA fragments produced by restriction enzyme digestion. The fragments were hybridized to mouse probes specific for class I, class II, and C4 genes. The analysis has revealed that the Smh complex contains as many class I genes as the mouse does and that these genes are polymorphic. The number of class II genes could not be determined with certainty, but it is probably not greater than in the mouse. Polymorphism was also detected at the loci coding for the complement component 4 (C4), which are probably closely linked to the Smh complex. The polymorphism of mole-rat class I loci contrasts with the reported monomorphism of these loci in the Syrian hamster. Since the mole-rat leads a solitary, subterranean life, as the Syrian hamster does, ecology cannot be an explanation for the lack of class I polymorphism in the latter species.
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