IL21 and tuberculosis: In this study, we demonstrate for the first time that NKT cells isolated from pleural fluid mononuclear cells (PFMCs) from TB patients produce IL-21 following stimulation with M. tuberculosis (Mtb)-specific antigens and that IL-21 is able to induce the production of IgG and IgA by B cells, which might influence the local immune response to M. tuberculosis in TB patients.