Human CD46 was identified as a complement regulator and was later shown to be a measles virus receptor. The ubiquitous distribution profile of CD46 accounted for systemic measles infection and general protection of host tissue/organs from autologous complement. A similar ubiquitous distribution was observed for swine and simian CD46 homologues based upon subsequent cDNA cloning and Northern analysis, reinforcing the roles of CD46. In contrast, recent cDNA cloning and distribution analyses of murine and guinea-pig CD46 revealed the predominant expression of these rodent CD46 homologues in the testis, especially in mature testicular germ cells. These results do not support the established functions of human CD46 but support the hypothesis that CD46 on sperm serves as a fertilization-related adhesion molecule toward eggs. Here, we review the structure, function and distribution of human CD46 and discuss the possible differences between human CD46 and its homologues recently cloned from a variety of non-human primates and other animals.

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