Trichomonas vaginalis haemolysis : pH regulates a contact-independent mechanism based on pore-forming proteins

There is a controversy in literature about involvement of secreted factors in the pathogenetic mechanisms of Trichomonas vaginalis, described mostly as contact-dependent. We found that the protozoan, under triggering conditions, is able to release molecules that lead to lysis without direct contact between parasite and target cell as a prerequisite. In this paper we characterize contact-independent cytotoxicity using the red blood cell as a cellular model. Contact-independent haemolysis is a phenomenon where pH exerts a key role, triggering the secretion of a lytic molecule and regulating its activity. A partial physicochemical characterization of the haemolytic factor suggests that a protein of M(r)>30 kDa could be the effector responsible for damage. Furthermore, the parasite-induced membraned permeabilization, detected by measuring potassium escape from the target cell, and an effective osmotic protection by carbohydrates allowed us to relate the previously described pore-forming mechanism involved in contact-dependent cytotoxicity with the contact-independent lysis.