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Systems and Processes

Antigen Processing and Presentation

In order to be capable of engaging the key elements of adaptive immunity (specificity, memory, diversity, self/nonself discrimination), antigens have to be processed and presented to immune cells. Antigen presentation is mediated by MHC class I molecules, and the class II molecules found on the surface of antigen-presenting cells (APCs) and certain other cells.

Complement System

Complement was discovered by Jules Bordet as a heat-labile component of normal plasma that causes the opsonisation and killing of bacteria. The complement system refers to a series of >20 proteins, circulating in the blood and tissue fluids. Most of the proteins are normally inactive, but in response to the recognition of molecular components of microorganisms they become sequentially activated in an enzyme cascade – the activation of one protein enzymatically cleaves and activates the next protein in the cascade.

Phagocytosis

Phagocytosis is a specific form of endocytosis by which cells internalise solid matter, including microbial pathogens. While most cells are capable of phagocytosis, it is the professional phagocytes of the immune system, including macrophages, neutrophils and