Antigenic Analysis of Virulent and Avirulent Strains of Trichomonas gallinae by Gel Diffusion Methods*

SYNOPSIS. Antigenic constitution of 5 Trichomonas gallinae strains and substrains was analyzed by gel diffusion technics. Fresh isolates of the very virulent JB and of an avirulent SG strain as well as avirulent substrains JBC and SGC, derived from JB and SG respectively by prolonged in vitro cultivation, were used in the experiments. An originally avirulent AG strain that was attenuated still further and lost its infectivity for pigeons during many years of serial transfers in nonliving media also was analyzed. Two major groups of antigens, A and B, were differentiated on the basis of precipitin line patterns formed in gel diffusion reactions involving the 5 strains and substrains and antisera prepared in rabbits against each of these trichomonad stocks. Group A was subdivided further into subgroups A] and (A). JB, JBC, AG, and SGC trichomonads appeared to share all or nearly all antigens of both these subgroups, but AG strain contained some unique A] and (A) antigens in addition to those which it had in common with the remaining 4 strains and substrains. Group B antigens were divided into 5 subgroups, B₁ to B₅. The complete B₁ antigenic complex was found in JB and JBC trichomonads and part of this complex was present also in SG strain and SGC substrain. In all instances, subgroup B₁ antigens stimulated production of specific antibodies in rabbits and combined with these antibodies present in immune sera. The complete B₂ antigenic complex was found only in JBC substrain. Some subgroup B₂ antigens were present also in JB trichomonads. Very few of these, however, were capable of stimulating antibody production in rabbits. The more numerous B₂ elements of JB strain that did not stimulate immunologic responses in rabbits, might be in the form of incomplete hapten-like antigens. All subgroup B₂ antigens found in JB strain represented only a portion of the B₂ complex associated with JBC substrain. Subgroup B₂ was characteristic of SG and SGC trichomonads, the latter substrain differing from the parental SG strain in the levels of both B₂ and B₁ antigens; these differences, however, were purely quantitative. JB strain reacted with some of subgroup B₃ antibodies present in SG and SGC antisera, but failed to stimulate antibody formation against any of these antigens in rabbits. The B₃ elements of JB trichomonads might be incomplete antigens. AG strain was characterized by having B₄ and B₅ antigenic complexes. The very small part of subgroup B₄, represented by a weak precipitin line in reactions between JB strain or JBC substrain and anti-AG serum, suggested the presence of some incomplete B₄ antigens in these trichomonads. Irrespective of whether freshly isolated avirulent strains or substrains attenuated by prolonged in vitro cultivation are examined by gel diffusion, such organisms are found richer in subgroup B antigens than the fully virulent JB trichomonads. All the results suggest that there may be a direct relationship between antigenic constitution and virulence of T. gallinae strains.