IgG Fc Control Proteins

There are five classes of immunoglobulins in humans, which are IgG, IgA, IgM, IgE and IgD. IgG can be further divided into four subclasses, IgG1, IgG2, IgG3 and IgG4 in humans, and IgG1, IgG2a, IgG2b and IgG3 in mice. IgG is abundant in serum with the longest half-life, which comprises 75% of immunoglobulins in circulation. IgG has a Y-shape structure with two identical light chains and two identical heavy polypeptide chains. The fragment crystallizable region (Fc region) represents the stem of the Y, which comprises two constant domains (CH2 and CH3) of the heavy chain. Fc region is responsible for effector functions through interactions with target molecules and receptors. Fc binding to Fc receptors on immune effector cells, such as natural killers and macrophages, elicits ADCC (antibody-dependent cell-mediated cytotoxicity), which leads to phagocytosis or lysis of the targeted cells. Fc region can also bind to complement components to mediate CDC (complement-dependent cytotoxicity). Mutations of Fc regions can improve or reduce their binding to molecules on effector cells as mentioned above.