Ageing affects the CD4+ T cell polarization and mucosal tropism induced by TLR2/TLR4-activated dendritic cells.

Toll-like receptor (TLR)2 activation induces aldehyde dehydrogenase enzymes in nonmucosal dendritic cells (DCs) enabling them to metabolize vitamin A into all-trans retinoic acid, which induces the expression of mucosal homing molecules (α4β7 and CCR9) in the activated T cells. Recently, we have shown that the simultaneous activation of nonmucosal DCs through TLR2 and TLR4 maintains such capacity while reinforcing the polarization of primed CD4+ T cells towards Th1. Here, we observed that TLR2/TLR4 stimulation of aged DCs leads to the production of less TNFα and more IL-10 and that CD4+ T cells primed by those DCs express lower levels of the mucosal homing receptor CCR9 and produce less type-1 (IFNγ) and more type-2 (IL-4 and IL-13) cytokines. These results emphasize the importance of considering the age-related alterations in DC function when developing novel immunomodulation strategies that rely on the DC-T cell crosstalk through stimulation of pattern recognition receptors.