I once heard a well-known scientist (I think it was Kary Mullis, but I’m not completely sure) opine that the introduction of human semen into the bloodstream would drive the immune system absolutely crazy. He was discoursing on the possibility of AIDS and other “gay” illnesses originating with anal sex and semen entering the bloodstream through tears in the rectal wall.
In early days of aids epidemic...semen entering blood stream was considered as possible cause of immunosuppression...cuz that is what happens when semen enters blood..it turns out there was this pesky little virus getting in...what could go wrong?