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Antibodies may also tag tumor cells or virally infected cells, with NK cells responding via the FcR; this process is known as antibody-dependent cellular cytotoxicity (ADCC). [5] Both IgM and IgG undergo conformational change upon binding antigen that allows complement protein C1q to associate with the Fc region of the antibody. [4]
1) Antibodies (A) and pathogens (B) circular in the blood. 2) The antibodies bind to pathogens with complementary antigen sequences, engaging in opsonization (2a), neutralisation (2b), and agglutination (2c). 3) A phagocyte (C) approaches the pathogen, and Fc region (D) of the antibody binds to one of the Fc receptors (E) on the phagocyte.
C3b is potent in opsonization: tagging pathogens, immune complexes (antigen-antibody), and apoptotic cells for phagocytosis. Additionally, C3b plays a role in forming a C3 convertase when bound to Factor B (C3bBb complex), or a C5 convertase when bound to C4b and C2b (C4b2b3b complex) or when an additional C3b molecule binds to the C3bBb ...
The classical complement pathway can be initiated by the binding of antigen-antibody complexes to the C1q protein. The globular regions of C1q recognize and bind to the Fc region of antibody isotypes IgG or IgM. [2] These globular regions of C1q can also bind to bacterial and viral surface proteins, apoptotic cells, and acute phase proteins. [5]
Thus it can form covalent amide or ester linkages with the plasma membrane of the pathogen and any associated antibodies, where it then behaves as an opsonin. The larger C2b produced by C2 hydrolysis attaches to the C4b to form the classical C3 convertase, C4b2b (formerly called C4b2a).
The classical and alternative complement pathways. Alternative pathway. (Some labels are in Polish.) The alternative pathway is a type of cascade reaction of the complement system and is a component of the innate immune system, a natural defense against infections.
Humoral immunity is also referred to as antibody-mediated immunity. The study of the molecular and cellular components that form the immune system , including their function and interaction, is the central science of immunology .
Mechanism of class-switch recombination that allows isotype switching in activated B cells. Immunoglobulin class switching, also known as isotype switching, isotypic commutation or class-switch recombination (CSR), is a biological mechanism that changes a B cell's production of immunoglobulin from one type to another, such as from the isotype IgM to the isotype IgG. [1]