On the basis of the evidence presented here we cannot distinguish between these two hypotheses. However, during preparation of this work for publication we became aware of a sequence in the Genbank database describing a rat sperm isoantigen (designated E-3) that was identical to that for the 24-kDa antigen. A subsequent publication describing the cloning and expression of this isoantigen by Northern blot analysis revealed that E-3 transcripts are tissue specific and detectable only in the corpus and cauda epithelium. buy claritin online
This evidence clearly favors the common epitope hypothesis, although processing of the 2D6 carbohydrate antigen still has to be invoked to explain why the high-molecular-mass components observed in fluid and on spermatozoa in the distal caput lose their reactivity to the McAb in the cauda region. The epididymis is well known to be a rich source of exoglycosidases, and it has long been speculated that they function to remove oligosaccharides from sperm surface glycoproteins. If this interpretation is correct, then the current work represents strong evidence for carbohydrate epitope processing during sperm maturation in the epididymis. Equally intriguing is that 2D6 reactivity is species specific, hinting that in the rat epididymal glycoproteins are preferentially O-glycosylated rather than Л-glycosylated.