Innate immunity signaling

Innate immunity response is an ancient self-defence mechanism, which is conserved across a very broad spectrum of species. The innate immune system constitutes the first line of host defense during infection or homeostatic regulatory activities and therefore plays a crucial role in the initial recognition and regulation of immune responses to invading organisms. Peripheral mononuclear phagocytes (MP; monocytes, tissue macrophages and dendritic cells) respond to pathogens but in molecular pattern-specific manners using phagocytosis and clearance mechanisms for intracellular killing. In the central nervous system (CNS), those are perivascular and brain macrophages and microglia. Of relevance they are separated from the antigen specific and long-lasting adaptive immune system, thus MP provide immediate surveillance responses against invading microbial pathogens and cancerous cells in the CNS. Of particular importance to the CNS, innate immunity can be both neuroprotective or neurodestructive contingent on the activation responses and phenotype that has emerged. In reference to phylogeny, MP-governed innate immunity strongly recapitulates ontogeny as it represents evolutionary primitive defense that is self-contained at a single cell level. It is operative in all species from single cell organisms to plants and, insects and inevitably conserved to man.