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An autoantibody that reacts with cardiolipin. Different immunoglobulin subclasses and isotypes are associated with different diseases and conditions. Some anticardiolipin antibodies prolong phospholipid dependent clotting while others are associated with spontaneous abortion.
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A protein complex comprised of one T-cell surface glycoprotein CD3 delta chain (CD3D), one T-cell surface glycoprotein CD3 gamma chain (CD3G) and two T-cell surface glycoprotein CD3 epsilon chains (CD3E). CD3D, CD3G and CD3E are transmembrane proteins with one extracellular immunoglobulin domain and one intracellular ITAM domain. The CD3 complex is a T-cell co-receptor that noncovalently associates with either the disulfide bound heterodimeric alpha/beta T-cell receptor (TCR) or gamma/delta TCR and two copies of the accessory protein, T-cell surface glycoprotein CD3 zeta chain (CD247), which is a transmembrane protein with three ITAM domains. The TCR moiety of the TCR-CD3 complex binds to MHC and processed antigens on antigen presenting cells, which triggers phosphorylation of and cellular propagation of the signal by CD247 and the CD3 complex.
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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.
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Hepatitis A virus cellular receptor 1 (359 aa, ~39 kDa) is encoded by the human HAVCR1 gene. This protein is involved in the modulation of asthma and allergic reactions.
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IgA is the immunoglobulin subclass that is associated with antibody-mediated mucosal immunity. It is secreted as dimers into the mucosa and is the most effective isotype at fixing complement by the alternative pathway, even though it lacks the ability to fix complement by the classical pathway. There are two subtypes in the human - IgA1 and IgA2.
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An immunoglobulin isotype (subclass). This isotype is expressed on naive B cells along with IgM. Little is known about its physiologic role.
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An immunoglobulin isotype (subclass). This isotype has the unique ability to bind with high affinity to IgE receptors (FceRI) on mast cells and basophils and induce degranulation and cytokine production by these cells when they are crosslinked by antigen. In addition to a central role in atopy and allergic responses, it has been speculated that IgE-mediated mast cell degranulation, by its release of mediators that increase vascular permeability, has an important role in the initiation of immune response in general.
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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.
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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.
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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.
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Along with the immunoglobulin G4 subclass (IgG4), the IgG3 subtype makes up a minor part of circulating antibodies in healthy individuals. The core hinge sequence contains approximately four times the number of amino acids as the other subclasses; allotypes of IgG3 can have up to 62 hinge residues and up to four interchain disulfide bonds. The increased hinge size for IgG3 increases the separation between the Fc (constant fragment) tail and Fab (antigen binding fragment) arms of antibodies of this subclass. This enhances the relative flexibility of the molecule, which may modulate antigen-binding capacity and immune complex formation, and may increase the affinity for binding to both Fc receptors and complement component C1q.
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Along with the immunoglobulin G3 subclass (IgG3), the IgG4 subtype makes up a minor part of circulating antibodies in healthy individuals. The IgG4 core hinge sequence contains 12 amino acids and two interchain disulfide bonds.This subtype has moderate affinity for binding Fc receptors and does not bind complement component C1q. The production of IgG4 can be stimulated following repeated or long-term exposure to antigen. Elevated levels are found in various diseases and infections and can be indicative of an fibroinflammatory syndrome known as IgG4-related disease.
