Three types of response to mycobacterial antigens

Responses to pathogenic and environmental mycobacteria were assessed in 2680 children in India and Sri Lanka using quadruple skin-testing with new tuberculins. Statistical analysis of the results, by fitting a log-linear mixture model, confirmed the presence of three different categories of response: category 2 non-responders (about 55%) did not react to any component of the mycobacteria; category 3 responders (about 40%) were sensitive to the species-specific group iv antigens; and category 1 responders (about 5%) were sensitive to the group i antigens which are common to all mycobacteria. The proportions of the three response categories vary with age and with BCG status. BCG vaccination and increasing age act independently to decrease the proportion of category 2 non-responders and increase the proportion of category 3 individuals. BCG vaccination and increasing age interact to increase the proportion of category 1 responders.