Innate Immune Mechanisms: Nonself recognition

The initial defence of the body against pathogens relies on the innate immune system. The innate immune system recognises unique molecular patterns expressed by pathogens, referred to as pathogen-associated molecular patterns (PAMPs), through receptors known as pattern recognition molecules (PRMs). PRMs are a diverse range of molecules and include secreted proteins, transmembrane proteins and cytosolic proteins. These molecules sense extracellular and intracellular pathogens and induce a number of responses to help aid in pathogen destruction including phagocytosis through opsonisation, cytokine production and activation of complement. In addition to pathogen sensing, host cells express proteins, the complement regulatory proteins that protect them from attack by the alternative pathway of complement activation, whereas foreign organisms lack these protective proteins and are, therefore, susceptible to complement attack.