A light and electron microscopial study of the mechanisms of pathogenecity of Trichomonas vaginalis in epithelial cell cultures.

J. P. HEATH: A light and electron microscopical study of the mechanisms of pathogenicity of Trichomonas vaginalis, in epithelial cell cultures. T. vaginalis is a urogenital protozoan parasite of man, causing the disease known as trichomoniasis. In males the disease is often symptomless; in females acute infections are often associated with inflammation of the cervical and vaginal walls, superficial erosions of the vaginal epithelium and a heavy, purulent vaginal discharge. In this study I have used an in vitro model of trichomoniasis in order to elucidate some of the mechanisms of pathogenicity of the parasite. The behaviour and cytopathogenicity of T. vaginalis in epithelial cell cultures was examined using phase contrast and interference reflection light microscopy, and scanning and transmission electron microscopy. The trichomonads attack the epithelial cell monolayers causing pathological changes within the cells which lead to the detachment and lysis of the cells. The lysed cell debris is phagocytosed by the trichomonads. Two aspects of the behaviour of T. vaginalis are of prime importance in the pathogenic processes that lead to the death of the cell cultures: 1) T. vaginalis readily adheres to the exposed surfaces of the epithelial cells and to the glass substratum on which the cells are grown. The adhesions are of the intermediate junction type, characterised by a gap of 10 - 20 nm. Damage to the monolayer of epithelial cells is restricted to those cells with adherent trichomonads. 2) When T. vaginalis adheres to a solid substratum it loses its characteristic spherical shape which is assumed in suspension and it develops pseudopodia which it uses to locomote in an amoeboid manner. The amoeboid trichomonads are capable of migrating between and under the monolayer mechanically breaking the adhesions of the cells to each other and to the substratum. The pseudopodia, and regions of active phagocytosis, of T. vaginalis contain actin-like microfilaments. Mechanisms that may be involved in the adhesiveness and amoeboid movements of T. vaginalis are discussed, and the possible relevance of these phenomena and of chemical factors to the cytopathogenicity of T. vaginalis in cell cultures and in humans is considered.