Spectrum of immune reactivity to mycobacterial (BCG) antigens in healthy hospital contacts in South India

In an effort to study the immunological responses to antigens of tubercle bacilli, 49 tuberculin positive and 41 tuberculin negative hospital contacts aged 20–29 years (staff nurses and students working in Government Rajaji Hospital, Madurai, South India) were studied for serum antibodies (IgG, IgM and IgA classes) to BCG by ELISA and diameter of induration to PPD by Mantoux procedures. The two immunological parameters were correlated in regression analysis. The results have revealed higher anti-BCG serum antibody levels in hospital contacts than in non-contacts, significantly higher antibodies in tuberculin negative hospital contacts than in tuberculin positive hospital contacts, an inverse correlation of tuberculin reactivity and antibodies and a bimodal decline (regression) of antibodies against the increase in skin test induration. This study has thus suggested the existence of an immunological spectrum in hospital contacts from south India; persons at one pole of the spectrum were tuberculin negative and possessed significantly elevated antibody levels and those at the other pole of the spectrum were tuberculin positive and possessed low antibody levels. Thus the spectrum of immune reactivity may be due to an inherent susceptibility/ resistance of an individual to Mycobacterium tuberculosis.