Indicators
A protein complex composed of 18 complement component 1q (C1q) subcomponent chains: six C1qA, six C1qB and six C1qC. The C1q complex is part of the complement component C1 complex (C1 complex) and undergoes confirmational rearrangement following binding of pentraxins or antigen-antibody complexes that include either immunoglobulin M (IgM) or several IgG molecules. These confirmational changes activate the C1r chains of the C1 complex, which, in turn, cleaves C1s chains of the C1 complex. Following C1s cleavage, the C1 complex can proteolytically activate C2 and C4 and promotes formation of C3-convertase, which cleaves C3 and activates the classical complement pathway.
Indicators
An immunoglobulin isotype (subclass) that characterizes secondary immune responses. This isotype is further broken down into several smaller subclasses (IgG1, IgG2a, IgG2b, IgG3 in the mouse; IgG1-4 in the human), and each subclass is differentially synthesized and secreted into the serum upon differential immune stimuli.
Indicators
The most abundant immunoglobulin G (IgG) subclass in the circulation of healthy individuals. The IgG1 core hinge sequence contains 15 amino acids and two interchain disulfide bonds. This subtype has high affinity for binding both Fc receptors and complement component C1q. IgG1 is the predominant antibody subclass that responds to antigens derived from both soluble and membrane proteins. Reduced levels of circulating IgG1 can indicate the presence of a variety of primary and secondary antibody deficiencies, which can result in hypogammaglobulinemia.
Indicators
The second most abundant immunoglobulin G (IgG) subclass in the circulation of healthy individuals. The IgG2 core hinge sequence contains 12 amino acids and up to four interchain disulfide bonds. This subtype has low affinity for binding both Fc receptors and complement component C1q. The production of this IgG2 is stimulated by exposure to bacterial capsular polysaccharides and other antigenic glycans.
