Identification and partial characterization of an immunoglobulin A protease associated with human sperm.

The ability of human sperm to evade local humoral immune response at the female genital tract has received little attention. As some microorganisms inactivate secretory immunoglobulin A (S-IgA) by enzymatic degradation as a part of their pathogenic mechanism, we decided to test the hypothesis that there is an IgA protease in human semen that helps sperm to progress through the cervix uteri. Incubation of different semen fractions in the presence of S-IgA revealed IgA protease activity associated with raw semen or sperm but not with seminal plasma; raw semen and sperm produced two split products of 66 kDa and 45 kDa, respectively, in SDS-PAGE. The enzymatic activity was blocked with EDTA. IgG and IgM were not digested under the same experimental conditions. Degradation of S-IgA by an IgA protease on the sperm surface may be among the mechanisms present in semen that enable sperm to evade an immune response in the female genital tract.