Decreased frequencies of circulating CD4⁺ T follicular helper cells associated with diminished plasma IL-21 in active pulmonary tuberculosis.

Kumar, N.P .; Sridhar, R .; Hanna, L.E .; Banurekha, V.V.; Nutman, T.B .; Babu, S .

PLoS One; 2014; 9; e111098.

Abstract: Background: Circulating T follicular helper (Tfh) cells represent a distinct subset of CD4⁺ T cells and are important in immunity to infections. Although they have been shown to play a role in experimental models of tuberculosis infection, their role in human tuberculosis remains unexplored.

Aims/Methodology: To determine the distribution of circulating Tfh cells in human TB, we measured the frequencies of Tfh cells ex vivo 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.

Results: We found that both ex vivo and TB - antigen induced frequencies of Tfh cell subsets was significantly lower in PTB compared to LTB individuals. Similarly, antigen induced frequencies of Tfh cells expressing IL-21 was also significantly lower in PTB individuals and this was reflected in diminished circulating levels of IL-21 and IFN g . This was not accompanied by diminished frequencies of activated or memory B cell subsets. Finally, the diminution in frequency of Tfh cells in PTB individuals was dependent on IL-10, CTLA-4 and PD-L1 in vitro .

Conclusions: Thus, PTB is characterized by adiminution in the frequency of Tfh cell subsets.

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