This family consists of seminal vesicle autoantigen and prolactin-inducible (PIP) proteins. Seminal vesicle autoantigen (SVA) is specifically present in the seminal plasma of mice. This 19-kDa secretory glycoprotein suppresses the motility of spermatozoa by interacting with phospholipid. PIP, has several known functions. In saliva, this protein plays a role in host defence by binding to microorganisms such as Streptococcus. PIP is an aspartyl proteinase and it acts as a factor capable of suppressing T-cell apoptosis through its interaction with CD4 [1].

1: Identification of two rodent genes encoding homologues to seminal vesicle autoantigen: a gene family including the gene for prolactin-inducible protein. Yoshida M, Kaneko M, Kurachi H, Osawa M; Biochem Biophys Res Commun 2001;281:94-100. PMID:11178965