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Early stages in the interaction between Mycoplasma gallisepticum and the chick trachea, as related to pathogenicity and immunogenicity.

Mycoplasma strains, which occur naturally or as the result of laboratory manipulation, differ markedly in biological properties such as pathogenicity, infectivity, transmissibility, and immunogenicity. These properties are clinical expressions of a series of complex interactions between the mycoplasma organisms and the host. We have focused on the early interactions occurring at the level of the tracheal mucosa, with the intent of identifying Mycoplasma gallisepticum strains possessing a combination of properties suitable for use in a live vaccine. The ability of a strain to colonize the chick trachea was evaluated by reisolation from the infected organ, expressed as infective dose (ID50). In addition to studies in the live chick, we have employed an in vitro model system for the study of adherence of the mycoplasmas to human red blood cells (RBC). Several strains that colonized the chick trachea were studied, multiplying profusely in close proximity to the epithelial surface, but producing only moderate or transient tissue damage in vivo. Adherence in vivo occurred via the "bleb" region of the M. gallisepticum organisms. A serological response was elicited by colonizing pathogenic or nonpathogenic M. gallisepticum but not by strains that were found by other methods to be readily eliminated from the tracheal surface.