Humoral pattern recognition and the complement system

TY - JOUR

T1 - Humoral pattern recognition and the complement system

AU - Degn, S E

AU - Thiel, Steffen

N1 - © 2013 John Wiley & Sons Ltd.

PY - 2013/8

Y1 - 2013/8

N2 - In the context of immunity, pattern recognition is the art of discriminating friend from foe and innocuous from noxious. The basis of discrimination is the existence of evolutionarily conserved patterns on microorganisms, which are intrinsic to these microorganisms and necessary for their function and existence. Such immutable or slowly evolving patterns are ideal handles for recognition and have been targeted by early cellular immune defence mechanisms such as Toll-like receptors, NOD-like receptors, RIG-I-like receptors, C-type lectin receptors and by humoral defence mechanisms such as the complement system. Complement is a proteolytic cascade system comprising around 35 different soluble and membrane-bound proteins. It constitutes a central part of the innate immune system, mediating several major innate effector functions and modulating adaptive immune responses. The complement cascade proceeds via controlled, limited proteolysis and conformational changes of constituent proteins through three activation pathways: the classical pathway, the alternative pathway and the lectin pathway, which converge in common effector functions. Here, we review the nature of the pattern recognition molecules involved in complement activation, as well as their close relatives with no or unknown capacity for activating complement. We proceed to examine the composition of the pattern recognition complexes involved in complement activation, focusing on those of the lectin pathway, and arrive at a new model for their mechanism of operation, supported by recently emerging evidence.

AB - In the context of immunity, pattern recognition is the art of discriminating friend from foe and innocuous from noxious. The basis of discrimination is the existence of evolutionarily conserved patterns on microorganisms, which are intrinsic to these microorganisms and necessary for their function and existence. Such immutable or slowly evolving patterns are ideal handles for recognition and have been targeted by early cellular immune defence mechanisms such as Toll-like receptors, NOD-like receptors, RIG-I-like receptors, C-type lectin receptors and by humoral defence mechanisms such as the complement system. Complement is a proteolytic cascade system comprising around 35 different soluble and membrane-bound proteins. It constitutes a central part of the innate immune system, mediating several major innate effector functions and modulating adaptive immune responses. The complement cascade proceeds via controlled, limited proteolysis and conformational changes of constituent proteins through three activation pathways: the classical pathway, the alternative pathway and the lectin pathway, which converge in common effector functions. Here, we review the nature of the pattern recognition molecules involved in complement activation, as well as their close relatives with no or unknown capacity for activating complement. We proceed to examine the composition of the pattern recognition complexes involved in complement activation, focusing on those of the lectin pathway, and arrive at a new model for their mechanism of operation, supported by recently emerging evidence.

KW - Antigen-Antibody Complex

KW - Complement Pathway, Alternative

KW - Complement Pathway, Classical

KW - Complement Pathway, Mannose-Binding Lectin

KW - Complement System Proteins

KW - Gene Expression Regulation

KW - Humans

KW - Immunity, Humoral

KW - Immunity, Innate

KW - Models, Immunological

KW - Protein Multimerization

KW - Proteolysis

KW - Receptors, Pattern Recognition

U2 - 10.1111/sji.12070

DO - 10.1111/sji.12070

M3 - Journal article

C2 - 23672641

SN - 0300-9475

VL - 78

SP - 181

EP - 193

JO - Scandinavian Journal of Immunology

JF - Scandinavian Journal of Immunology

IS - 2

ER -