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.