Innate immune sensing and activation of cell surface Toll-like receptors.

The expansion of sensing function by cell surface Toll-like receptors (TLRs) has grown to include not only more diverse viral, bacterial, fungal and protozoan surface components, but also a plethora of endogenous molecules arising from host cell and tissue damage as well as the inflammatory response itself. This flexibility in recognition is accommodated not only by physical and structural features of the TLRs themselves, but also by additional innate immune receptors, soluble molecules and subcellular trafficking mechanisms. These events have begun to reveal a remarkable plasticity and complexity within this critical arm of the host innate immune system.