antibodyprotein

Antibodyprotein refers to antibodies, or immunoglobulins, which are large glycoproteins produced by B cells and plasma cells. They recognize specific antigens and play a central role in adaptive immunity, facilitating pathogen neutralization, opsonization, and activation of other immune components.

Antibodies are built from four polypeptide chains: two identical heavy chains and two identical light chains, linked by disulfide bonds. The molecule has a Y-shaped structure with antigen-binding fragments (Fab) at the tips and a crystallizable fragment (Fc) at the stem. The variable regions of the heavy and light chains form the antigen-binding site, determining specificity, while the constant regions define the antibody class and effector functions. Glycosylation influences stability and activity.

Functionally, antibodies bind to antigens to neutralize pathogens, block entry into cells, or mark invaders for attack by other parts of the immune system. Fc region interactions recruit complement, phagocytes, and natural killer cells, enabling pathways such as opsonization and antibody-dependent cellular cytotoxicity. Isotype switching allows a B cell to change the class of antibody it produces without altering antigen specificity, tailoring the immune response to different tissues and threats.

There are five major classes of antibodies: IgG, IgA, IgM, IgD, and IgE, with various subclasses. IgM is typically produced early in an infection and forms pentamers; IgG is the most abundant in blood and tissues; IgA predominates in mucosal surfaces; IgE is involved in allergic responses; IgD's precise roles are less well defined.

Production and applications: in the immune system, antibodies are generated by B cells and plasma cells. Therapeutic antibodies are produced recombinantly in mammalian cell culture and used as monoclonal antibodies, while polyclonal antibodies can be derived from immunized animals or humans. In diagnostics, antibodies underpin assays such as ELISA, Western blot, and immunohistochemistry.

Clinical relevance: abnormal antibody production or function can lead to immunodeficiencies, autoimmunity, or hypersensitivity. Antibody-based therapies and diagnostics are essential tools in medicine.