Immunological analysis of cells of Nocardia at various developmental stages during morphogenesis.

High antibody titres and a single precipitin line of identity were obtained with hyperimmune rabbit serum prepared against filamentous cells of Nocardia asteroides strain 55 and the cells of three other strains of Nocardia, indicating the presence of a group antigen between the strains. High titres were also obtained with the hyperimmune serum and the three different cell forms (filamentous, rod-like and spherical cells) of the homologous strain, indicating that each developmental stage was highly antigenic. The antibodies were completely removed by absorption with the various cell forms, suggesting a similarity of the antigens. A single common antigen was demonstrated between the three developmental stages by immunodiffusion, indicating that there was no antigenic alteration occuring during morphogenesis of the genus Nocardia.