METHODS Influence of HLA-DR antigens and lymphocyte responses in pulmonary TB patients. OBJECTIVE To elucidate the role of HLA-DR genes/gene products on lymphocyte responses to Mycobacterium tuberculosis antigens and mitogens, the present study was carried out in pulmonary tuberculosis during active and cured stage of the disease. METHODS Serological determination of HLA-DR antigens was carried out in 50 active TB patients, 44 cured TB patients and 58 normal healthy control subjects. The influence of HLA-DR antigens on peripheral blood lymphocyte responses to M. tuberculosis culture filtrate antigens and mitogens such as phytohaemagglutinin (PHA) and concanavalin-A (Con-A) was studied in the patients as well as normal healthy control subjects. RESULTS Of all the DR antigens studied, patients (active TB and cured TB) with DR2 antigen showed an increased lymphocyte response (stimulation index) to a higher dose of antigenic (10 micrograms/ml) stimulation. A significantly lower lymphocyte response to antigen and mitogens was seen in HLA-DR3 positive normal healthy subjects than non-DR3 (DR3 negative) subjects. CONCLUSIONS The present study suggests that HLA-DR genes/gene products may be playing an immunoregulatory role in eliciting an immune response against M. tuberculosis antigens and mitogens induced lymphocyte response in pulmonary TB patients and normal healthy subjects.