Dendritic cells and other innate determinants of T helper cell polarisation

• Innate immune cells shape the adaptive immune responses via T cell activation.
• Innate immune cells present antigen and provide signals for T cell activation.
• Different pathogen-derived molecules promote induction of distinct CD4 T cell subtypes.
• Regulatory cytokines produced by innate immune cells direct T cell responses.

Adaptive immunity plays a crucial role in natural host defence against pathogens and tumours, and is central to the long-term protective effect of vaccines. It is mediated by T and B cells that are activated through antigen-specific receptors. By contrast, innate immunity responds immediately to infection and damage, and is activated through binding of conserved pathogen or damage-associated molecules to pattern recognition receptors (PRRs) on dendritic cells (DCs) and other innate immunity cell types. Recent studies have demonstrated that the innate immune system also functions to direct the adaptive immune response, not only through antigen presentation but also by providing the key signals for the differentiation of naive CD4+ T cells into functionally distinct T helper (Th) cell subtypes.