CD55 and CD59 protein expression by Apodemus (field mice) sperm in the absence of CD46

The mammalian female reproductive tract has an abundance of complement components, which play a vital role in protection against genital pathogens. Sperm may be protected against complement-mediated damage by complement regulatory proteins, including membrane cofactor protein (CD46), decay accelerating factor (CD55) and CD59. However, sperm from Apodemus (field mice) do not express CD46 protein. The aim of the present study was to determine whether Apodemus sperm may be protected against complement-mediated damage by expression of CD55 and CD59 in the absence of CD46. We demonstrate here that, like Mus musculus mice (house mice), wild-caught Apodemus flavicollis, Apodemus microps and Apodemus sylvaticus mice express both glycosylphosphatidylinositol (GPI)- and transmembrane (TM)-anchored testicular CD55 mRNA transcripts. In Mus, testicular GPI- and TM-CD55 transcripts are generated by two distinct but closely related genes. We show that in contrast to Mus, CD55 isoforms in A. sylvaticus are generated by alternative splicing of a single copy gene. Testicular CD59 mRNA transcripts were also identified in A. flavicollis, A. microps, A. sylvaticus and M. musculus. CD55 and CD59 proteins are broadly distributed on epididymal sperm from wild-caught Apodemus and Mus mice as well as BALB/c mice, with expression on the acrosome, neck and tail. Thus, despite not expressing CD46 protein, Apodemus sperm may be protected against complement-mediated injury in the female genital tract by CD55 and CD59.