SYNOPSIS. Antisera were developed in rabbits against homogenized antigens prepared from 3 axenic lines of Trichomonas gallinae: JB(VI), the 6th isolate of the very virulent Jones' Barn strain which was kept frozen in liquid nitrogen and was fully pathogenic for pigeons at the time at which it was employed for immunization; JB (VI)C, a substrain derived from JB(VI), but attenuated during continuous in vitro cultivation for 1 year; and JB(V)C, a substrain of the 5th isolate of the Jones' Barn strain attenuated during continuous in vitro cultivation for over 3 years. Globulin fractions of the antisera were conjugated with fluorescein isothiocyanate (FITC), and fractionated on DEAE‐cellulose columns to yield highly specific fractions. Intact, formalin‐fixed flagellates of each line were stained on slides with each labelled antiserum under standardized conditions. Fluorescence emitted by individual organisms was measured with the aid of a special microfluorimetric apparatus. Experiments involving direct staining, one‐step inhibition, and cross‐absorption methods indicated the presence of unique and cross‐reacting antigenic systems in each of the 3 lines of trichomonads. The 2 substrains attenuated in the course of prolonged in vitro cultivation, altho antigenically similar, could be readily differentiated from each other. Further, both of them appeared to contain more antigenic systems than the still fully virulent JB(VI) parasites. Copyright © 1968, Wiley Blackwell. All rights reserved
