The lipopolysaccharide co-receptor CD14 is present and functional in seminal plasma and expressed on spermatozoa

CD14 is a 54 000-molecular weight (MW) glycolipid-anchored membrane glycopr otein. expressed on myeloid cells. which functions as a member of the lipop olysaccharide (LPS) receptor complex. Soluble forms of CD14 have been repor ted in plasma, cerebrospinal fluid, amniotic fluid and breast milk. In plas ma and breast milk, soluble CD14 has been implicated as a regulator of T- a nd B-cell activation and function. Expression of CD14 in the male reproduct ive system has not previously been investigated. We here show that soluble CD14 is present in seminal plasma at levels comparable to those in serum. S permatozoa expressed CD14 on their membranes, as demonstrated by fluorescen ce microscopy and flow cytometry. Post-vasectomy, the levels of seminal pla sma CD14 (spCD14) were much reduced, implying an origin distal to the point of transection of the vas deferens, Ultracentrifugation analyses demonstra ted that spCD14 was not associated with lipid complexes, indicating that it lacks the glycolipid anchor. Purified spCD14 mediated activation by LPS of CD14-negative cells. These findings suggest that CD14 may play a hitherto unexplored role in immune defence and cell activation in the male reproduct ive tract.