Detection of antigen in Nocardia caviae cross-reacting with mycobacterial antigen No. 21 in M. leprae using a lepromatous leprosy serum pool as antibody reagent.

Eighteen strains of nocardia, representing five different species, were studied in crossed immunoelectrophoresis against a lepromatous leprosy serum pool for the presence of antigen No. 21. This mycobacterial antigen shows antigenic heterogeneity with species specific antigenic determinants defined in Mycobacterium leprae. All four strains of N. caviae were found to share antigen No. 21 determinants with mucobacteria. All other strains of nocardia were negative in these direct immunoprecipitation tests. When compared with M. leprae antigen No. 21, the N. caviae antigen gave a reaction of partial identify in the same way as all strains of other mycobacteria tested previously, ii.e., with spurring by the M. leprae antigen. There was a reaction of complete identity between N. caviae and M. avium-intracellulare and M. smegmatis, respectively, with the lepromatous leprosy serum pool used as the antibody source. The results suggest that N. caviae antigen No. 21 is more closely related to the corresponding antigen of the genus Mycobacterium than to the antigen No. 21 equivalent of other nocardia species tested.