In order to identify novel sperm alloantigens relevant to immune infertility, sera from infertile men that contained anti-sperm antibodies (ASA) were used on 2-D immunoblots of human sperm proteins.
ASA are thought to impair fertility by inhibiting sperm motility (Haas, 1987), sperm penetration of the cervical mucus (Haas, 1986), capacitation (Caron and Saling, 1991), or the acrosome reaction (Lee et al., 1995). An understanding of the mechanism behind immunologic infertility, as well as improved diagnosis and treatment, depends on knowledge of the identities of specific sperm antigens capable of eliciting the production of functionally relevant sperm antibodies. Using vectorial labeling and 2-D electrophoresis by isoelectric focusing IEF), the authors identified six auto- and iso-antigens that were not recognized by fertile sera and were possibly relevant to antibody-mediated immunoinfertility. Further studies led to the identification and characterization of several post-meiotically expressed sperm alloantigens residing in the acrosomal membranes and equatorial segment. The current study discovered an interesting alloantigen residing in the sperm tail. It is characterized in this report. Taken together, the findings call for adoption of a different name for h-meichroacidin (hMCA). The authors propose radial spoke protein 44 (RSP44) as a more accurate designation for the hMCA protein. The current name TSGA2 suggests incorrectly that it is a testis specific gene. Bioinformatic comparisons support the conclusion that RSP44 is an "ancestral gene" conserved during evolution and present in mammalian sperm. The central role of the axoneme in flagellar movement and the localization of RSP44 to the radial spokes suggest sperm motility and ciliary movement are important new dimensions in considering the functions of this recently annotated protein. 1 table, 7 figures, and 40 references