Prevalence of Antineutrophil Cytoplasmic Antibodies and Antinuclear Antibodies in Patients with Pulmonary Tuberculosis: A Tertiary Care Center Experience from North India

Background Tuberculosis (TB) can have manifestations closely mimicking autoimmune diseases. The prevalence of autoantibodies in TB varies among different populations. Objectives To study the prevalence of anti-neutrophilic cytoplasmic antibodies (ANCA) and antinuclear antibodies (ANA) in pulmonary tuberculosis (PTB). Methods This was a cross-sectional, observational study. Subjects with microbiologically confirmed PTB, either via smear or culture positivity on sputum or bronchoalveolar lavage (BAL) fluid, or positive rapid diagnostic tests were included. ANCA against proteinase-3 (PR3), myeloperoxidase (MPO), lactoferrin, and elastase were tested using an enzyme-linked immunosorbent assay (ELISA). ANA was detected using indirect immunofluorescence (IIF). Results Eighty-nine subjects with a median [interquartile range (IQR)] age of 28 (20-46) years, 67.4% males, were recruited. Eighty-one subjects had microbiological confirmation on sputum examination, and eight required examination of BAL fluid. Sera were drawn from 62 treatment-naïve subjects, the rest (27) were on antitubercular therapy (ATT). Eighty-six (96.6%) subjects tested positive for anti-elastase antibody, seven of which were also positive for anti-PR3. None were positive for anti-MPO and anti-lactoferrin. Six (6.7%) subjects tested positive for ANA. None of the subjects had features of underlying connective tissue disease or vasculitis. Conclusion PTB patients showed a high prevalence of anti-elastase and a low prevalence of ANA and anti-PR3 antibodies. ANCA positivity should be interpreted with caution in TB endemic areas. The role of anti-elastase antibodies in differentiating TB from ANCA-associated vasculitis (AAV) needs further research.