MAPping innate immunity.

T he capacity to mount an immune response that eliminates infection of a host by a microbial pathogen is critical for species survival and propagation. Mammals have developed complex immune systems that integrate innate responses, such as phagocytosis and the production of antimicrobial peptides after Toll-like receptor activation, along with adaptive responses, such as antibody production and activation of helper and cytotoxic T cell populations. By contrast, simpler organisms have much less complex immune systems that are focused exclusively on generating innate immune defenses. Over the last few years, it has become apparent that mitogenactivated protein (MAP) kinase (MAPK)signaling pathways play an essential and central role in the immune responses within each of these species.