ICOS and pulmonary tuberculosis: To determine the distribution of circulating Tfh cells in human TB, we measured the frequencies of Tfh cells exvivo and following TB - antigen or polyclonal stimulation in pulmonary TB (PTB; n = 30) and latent TB (LTB; n = 20) individuals, using the markers CXCR5, PD-1 and ICOS.