TLR2 and TLR4 expression on the immune cells of tuberculous pleural fluid.

Toll-like receptors (TLRs) play an important role in mediating the down stream signaling of immune response in tuberculosis. The predominance of Th1 response in tuberculous pleurisy prompted us to study the expression profiles of TLR2 and TLR4 on different immune cells and on subsets of T cells obtained from the site of infection. Our results showed that TLR2 was up-regulated on the monocytes from pleural fluid indicating a prominent role for this receptor in anti-tuberculous immunity. Notably, TLR2 and TLR4 expression were also enhanced on IFN-gamma secreting CD4(+)T cells. However, their expression was down-regulated on activated and IL-4 secreting CD4(+)T cells from the site of infection indicating that TLR expression is differentially modulated on the different subsets of T cells depending on their activation status and cytokine expression. The down-regulation of both TLRs on the natural regulatory T cells despite their higher number at the site of infection might be a mechanism to maintain their suppressive activity.