Phagocytosis

Antibody opsonization

Virus

Complement receptor

Alternative complement pathway

Complement component 3

Immunity

Biology

Gene

Classical complement pathway

Lytic cycle

Cell biology

Immunology

Genetics

Opsonin

Complement (music)

Innate immune system

Complement system

Complementation

Acquired immune system

Immune system

Phenotype

Annual Review of Immunology

The complement system is an evolutionarily ancient key component of innate immunity required for the detection and removal of invading pathogens. It was discovered more than 100 years ago and was originally defined as a liver-derived, blood-circulating sentinel system that classically mediates the opsonization and lytic killing of dangerous microbes and the initiation of the general inflammatory reaction. More recently, complement has also emerged as a critical player in adaptive immunity via its ability to instruct both B and T cell responses. In particular, work on the impact of complement on T cell responses led to the surprising discoveries that the complement system also functions within cells and is involved in regulating basic cellular processes, predominantly those of metabolic nature. Here, we review current knowledge about complement's role in T cell biology, with a focus on the novel intracellular and noncanonical activities of this ancient system.

Complement and the Regulation of T Cell Responses