Immunologic Analysis by Gel Diffusion of Effects of Prolonged Cultivation on Histomonas meleagridis (Smith)*

SYNOPSIS. Antigens were prepared from each of 4 lines of Histomonas meleagridis: Hm‐L1, a strain highly virulent for both turkeys and chickens; Hm‐L1/C12, Hm‐L1/C24, Hm‐L1/C52, 3 avirulent substrains derived from Hm‐L1 after 12, 24, 52 weeks of in vitro cultivation, respectively. Hm‐L1 strain and the 3 substrains were maintained in liquid nitrogen. Antisera were developed in rabbits against Hm‐L1 and Hm‐L1/C24 parasites. Both antisera were reacted on gel diffusion plates with homologous and heterologous antigens. Two groups of precipitin lines and/or bands designated arbitrarily as A and B, were observed on the slides. Analysis of these bands revealed the common antigenic composition of the 4 histomonads with respect to some of the group A and group B antigens. The concentrations and numbers of precipitin lines in both groups increased, however, with the length of cultivation. These antigenic differences are discussed in the light of their possible relationship to pathogenicity.