Function of complement regulatory proteins in immunity of reproduction: a review

Humoral immunity has an important role during the maturation and development of the functional properties of spermatozoa. Spermatozoa may be exposed to antisperm antibodies in semen and in cervical, ovarian follicular and fallopian fluid. Antisperm antibodies can be complement-fixing or non-fixing and may affect the reproductive functions in a number of ways. Although the antisperm antibody alone can cause sperm agglutination, complement fixation is required for their immobilization. Therefore, the complement activation might be a “keystone” for the better understanding of “sperm humoral immunity” and some types of infertility. Recently, three cell surface molecules (CD molecules – CD46, CD55, CD59) present on many tissues in male and female reproductive tracts and gametes have been identified. These proteins belong to the family of complement regulatory proteins which could regulate the function of a complement system by cleavage of complement cascade in discrete sites of both activation ways (classical and alternative). In this review, the particular mechanisms of activity of complement regulatory proteins are presented as well as their function in a fertilization process and expression in human and animal tissues and organs.