Q.What are the functions of immunoglobulin ?

Immunoglobulins (antibodies) are antigen-specific proteins secreted by plasma cells that neutralise, opsonise, agglutinate and help destroy pathogens as the effector molecules of humoral immunity.

Immunoglobulins are Y-shaped glycoproteins produced by plasma cells (the antibody-secreting descendants of activated B-lymphocytes) in response to a specific antigen. Their principal functions are: (1) Neutralisation — binding directly to toxins or to the surface proteins of viruses/bacteria, blocking their ability to bind host cells or exert their harmful (toxic) effect; (2) Opsonisation — coating the surface of a pathogen so that phagocytic cells (macrophages, neutrophils) recognise and engulf it more efficiently; (3) Agglutination — cross-linking multiple antigen-bearing particles or cells (such as bacteria) into clumps, which immobilises them and makes them easier for phagocytes to remove; (4) Precipitation — similarly cross-linking soluble antigen molecules to form insoluble complexes that can be cleared; and (5) Complement activation — certain antibody classes (mainly IgG and IgM), once bound to antigen, activate the complement cascade, which can directly lyse pathogens and further enhance opsonisation and inflammation. In addition, the five classes of immunoglobulins have specialised roles: IgG is the most abundant, is the main antibody of the secondary immune response, and is the only class that can cross the placenta to give …