Antibody Classification

Antibodies Classification According to The Physical and Functional Properties

In humans, five immunoglobulin-classes (IgG, IgM, IgA, IgD, and IgE) could be identified according to structural markers of the heavy chains (α, δ, ε, γ, and μ) and their multimeric assembly. In the context of the immune system, each isotype is expressed at different times of the immune response and initiates different immune cascades.

  • IgM is the first class of immunoglobulin produced after activation of B cells and tends to be of low affinity. IgM is found mainly in the bloodstream. The IgM antibody is secreted as a pentamer and has 10 antigen-binding sites, conferring higher overall avidity when binding to multivalent antigens. The pentameric structure of IgM makes it especially effective in activating the complement system.
  • IgA is the predominant antibody in mucous secretions such as saliva, tears, milk, and intestinal juice. IgA is mainly from the epithelial lining of the intestinal and respiratory tracts. IgA can form dimers and functions chiefly as a neutralizing antibody.
  • IgG is the principal class of antibodies in the blood and extracellular fluid. In humans, IgG is found as four subclasses (IgG1, IgG2, IgG3, and IgG4). IgG efficiently opsonizes pathogens for engulfment by phagocytes and activates the complement system. IgG provides long-term protection because it persists for months and years after the presence of the antigen that has triggered their production. Maternal IgG is transported across the placenta directly into the bloodstream of the fetus during intrauterine life.
  • IgE antibody is bound avidly by receptors on the basophils and mast cells that are found just beneath the skin and mucosa and along blood vessels in connective tissue. Antigen binding to this cell-associated IgE triggers mast cells to release powerful chemical mediators that induce reactions such as coughing, sneezing, and vomiting, which in turn can expel infectious agents.
  • IgD is coexpressed with IgM on the surface of almost all mature B cells but is secreted in only small amounts by plasma cells. IgD plays a role in the induction of antibody production. The unique function of IgD is still unclear and a matter of active research.

Antibodies Classification. Fig1 Antibodies Classification. (Zamora-Gálvez, 2017)

Other Classification

According to the object of action, the antibody can be divided into antitoxin antibody, antibacterial antibody, antiviral antibody, and cytotropic antibody that can be bonded to cells. According to the form of existence, the immunoglobulins are classified into the soluble antibody and the membrane-bound receptor. B-cell receptor (BCR) is a membrane-bound immunoglobulin on the B-cell surface as the cell’s receptor for antigen. A secreted immunoglobulin that binds pathogens or their toxic products in the extracellular spaces is the antibody produced by plasma cells.

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  1. Zamora-Gálvez, A.; et al. Nanomaterials connected to antibodies and molecularly imprinted polymers as bio/receptors for bio/sensor applications. Applied Materials Today. 2017, 9:387-401.

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