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2015 ; 6
(ä): 257
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Complement System Part II: Role in Immunity
#MMPMID26074922
Merle NS
; Noe R
; Halbwachs-Mecarelli L
; Fremeaux-Bacchi V
; Roumenina LT
Front Immunol
2015[]; 6
(ä): 257
PMID26074922
show ga
The complement system has been considered for a long time as a simple lytic
cascade, aimed to kill bacteria infecting the host organism. Nowadays, this
vision has changed and it is well accepted that complement is a complex innate
immune surveillance system, playing a key role in host homeostasis, inflammation,
and in the defense against pathogens. This review discusses recent advances in
the understanding of the role of complement in physiology and pathology. It
starts with a description of complement contribution to the normal physiology
(homeostasis) of a healthy organism, including the silent clearance of apoptotic
cells and maintenance of cell survival. In pathology, complement can be a friend
or a foe. It acts as a friend in the defense against pathogens, by inducing
opsonization and a direct killing by C5b-9 membrane attack complex and by
triggering inflammatory responses with the anaphylatoxins C3a and C5a.
Opsonization plays also a major role in the mounting of an adaptive immune
response, involving antigen presenting cells, T-, and B-lymphocytes.
Nevertheless, it can be also an enemy, when pathogens hijack complement
regulators to protect themselves from the immune system. Inadequate complement
activation becomes a disease cause, as in atypical hemolytic uremic syndrome, C3
glomerulopathies, and systemic lupus erythematosus. Age-related macular
degeneration and cancer will be described as examples showing that complement
contributes to a large variety of conditions, far exceeding the classical
examples of diseases associated with complement deficiencies. Finally, we discuss
complement as a therapeutic target.