Two Trichomonas vaginalis surface proteinases bind to host epithelial cells and are related to levels of cytoadherence and cytotoxicity.

Recent reports strongly suggest that cytoadherence and cytotoxicity by Trichomonas vaginalis require cysteine proteinase activity. Because of the large number of cysteine proteinases synthesized by T. vaginalis, a ligand assay was used to identify specific proteinases which may selectively target host cells. Two cysteine proteinases from trichomonal extracts with relative molecular masses (Mr) of 65,000 daltons (65-kDa) and 30-kDa were found to avidly bind to HeLa cell and vaginal epithelial cell surfaces. The two proteinases were distinguished by differential inhibition with leupeptin and N-alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK). Leupeptin pretreatment of live organisms inhibited the 30-kDa proteinase, which concomitantly reduced or eliminated cytoadherence. The T. vaginalis isolates with low levels of cytoadherence also had diminished or no detectable 30-kDa proteinase activity. On the other hand, TLCK pretreatment inhibited both the 30-kDa and 65-kDa proteinases, which resulted in decreased levels of cytoadherence and totally abolished contact-dependent cytotoxicity. Furthermore, isolates capable of attachment but with little or no cytotoxicity toward HeLa cells had no detectable host cell-bound 65-kDa proteinase. Finally, antiserum generated to each proteinase reacted by indirect immunofluorescence with live organisms, suggesting a surface location for both proteinases. This strategy and use of the ligand assay may permit for the deliniation of the role of two specific T. vaginalis surface proteinases in the properties of cytoadherence and cytotoxicity.