A sialoglycoprotein, gp20, of the human capacitated sperm surface is a homologue of the leukocyte CD52 antigen: analysis of the effect of anti-CD52 monoclonal antibody (CAMPATH-1) on capacitated spermatozoa

In this study we performed hi-terminal sequence analysis of gp20, a 20 kDa sialoglycoprotein on the human sperm surface previously identified by radio labelling of the sialic acid residues of sperm surface. We found 100% ident ity with the N-terminus of CD52, an antigen expressed on almost all human l eukocytes. We also show that, like CD52, gp20 behaves as a glycosylphosphat idylinositol (GPI)-anchored protein and that anti-gp20 antiserum reacts wit h an antigen on leukocytes of the same molecular weight as CD52. Using CAMP ATH-1, the monoclonal antibody against CD52, in fluorescent staining of cap acitated spermatozoa, Western blot analysis and the zona-free hamster egg p enetration test, we found that the effect of this antibody was different fr om that of our anti-gp20. Western blot analysis revealed a well-defined 20 kDa band with anti-gp20, whereas a 14-20 kDa band was detected with CAMPATH -1. Anti-gp20 stained the equatorial region of the sperm head, whereas CAMP ATH-1 stained the tail in immunofluorescence analysis of capacitated sperma tozoa. A dose-dependent inhibitory effect was seen with CAMPATH-1, similar to that previously detected with anti-gp20, in a zona-free hamster egg pene tration test. However, with CAMPATH-1 agglutination of motile spermatozoa w as detected, and this was not present with anti-gp20. This suggests that th e epitopes recognized by the two antibodies are different.