Effector functions of antibodies
Antibodies also known as immunoglobulins are secreted by plasma cells and B lymphocytes from the bone marrow and the lymphoid organs. The effector functions of antibodies are determined by the constant regions of the heavy chain. There are five different isotypes known in mammals to perform different roles and to direct a specific immune response for the antigen encountered. The binding of antigens to the variable regions will trigger the effector functions. Antibodies are only able to perform their functions upon entering the blood and the peripheral sites of infection. They prevent the entry of potential microbes through the epithelia. Antibodies are produced as early as the first week of vaccination or infection. Vaccination aims to produce long-lived plasma cells and memory cells. During the primary response to a microbe, plasma cells help to secrete small amounts of antibodies for a long period of time. If there is a repeated attack to the antigen, there will be a more effective defence against the infection as memory cells differentiate into antibody producing cells. Antibodies have both antigen-binding (Fab) regions and Fc regions to carry out different functions. The Fab region binds to the microbe and toxins to block the harmful effects. The Fc regions consist of heavy chain constant regions and binds to phagocytes and complement. However, it requires the antigen recognition by the Fab region. Isotype switching and affinity maturation occur in antibodies produced by antigen-stimulated B lymphocytes in response to protein antigens. Isotype switching causes the production of antibodies with distinct Fc regions with different effector functions. IgG carries out neutralization of toxins and microbes, activates the classical pathway of the complement and opsonisation of antigens for phagocytosis. It is the only class of immunoglobulin involved in neonatal immunity where it goes through the placenta and the gut to transfer the...
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