Immunoglobulin G Expression in Human Sperm and Possible Functional Significance

Immunoglobulin G (IgG), the major molecule of the immune system, which was traditionally thought to be produced by differentiated B-lymphocytes, had recently been found in non-immune cells including spermatozoa of rabbit testis. To study if human sperms could produce IgG that might play a role in fertilization, we employed immunofluorescent staining, Western blot, in situ hybridization, RT-PCR (reverse transcription polymerase chain reaction) and immunoelectron microscope and found that human sperms were capable of synthesizing IgG. IgG protein and mRNA were detected in the cytoplasm, mainly the neck region of the sperm and IgG immunoreactivity was found to cover the entire sperm cell. The essential enzymes necessary for IgG synthesis and class switching, RAG1 (recombination activating gene 1), RAG2 (recombination activating gene 2) and AID (activation-induced cytidine deaminase), were also detected in the sperm cells. Furthermore, we found that anti-IgG antibody could inhibit sperm from penetrating Zona-free hamster egg with statistical significance. These discoveries suggested that immunoglobulin G could be produced by human sperms and it might play a role during fertilization.