Abstract
The cross-reactivity of crude sonic extracts of six species of mycobacteria was studied by skin tests in mice and guinea pigs immunised with live Mycobacterium tuberculosis strain H37Rv, and in patients with pulmonary tuberculosis. All slowly growing mycobacteria elicited a strong delayed hypersensitivity response, M. vaccae a moderate response and M. phlei a poor or no response. A specific target antigen for cell-mediated immunity, known to be present in M. tuberculosis, was also present in all the mycobacteria studied. This shared antigen was shown, by immunoprecipitation tests, to be identical in all the slowly growing species but only a partial reaction of identity was obtained with M. phlei. It is concluded that the antigen shared by the slowly growing mycobacteria is immunodominant in cell-mediated immunity.