CXCR5 and tuberculosis: To determine whether Tfh cells are regulated by TB antigens in PTB, we used flow cytometry to first estimate the frequencies of CD4+ CXCR5+ PD-1+ ICOS−; CD4+ CXCR5+ PD-1− ICOS+ or CD4+ CXCR5+ PD-1+ ICOS+ T cells at baseline or following stimulation with TB antigens or anti-CD3.