CD55 and CD59 proteins are broadly distributed on epididymal sperm from Apodemus and Mus with expression on the acrosome, neck and tail. It can be inferred that Apodemus have traded expression of CD46 complement regulatory protein for acrosomal instability, providing a novel molecular basis underlying a genus-specific strategy to increase competitive advantage for sperm in the promiscuous reproductive behaviour of Apodemus.
Thus, despite not expressing CD46, Apodemus sperm are protected against complement-mediated injury in the female genital tract by CD55 and CD59.