tail piece (T- piece) which help the IgA to move across mucosa without degradation in secretions. There are two subclasses of IgA, IgA1 and IgA2, whose structures differ mainly in their hinge regions. They are IgA1 -Alpha 1 (α1) heavy chains and IgA2 -Alpha 2 (α2) heavy chains. IgA has a critical role in protection of mucosal surfaces from toxins, virus and bacteria by direct neutralization or by prevention of binding to the mucosal surface. Intracellular IgA may also be important in preventing bacterial or viral infection and/or pathogenesis. It can bind to Fc receptors on some cells as PMN cells and lymphocytes. It does not normally fix complement (unless aggregated)(Woof andMestecky, 2005). 4- IgD: It is found in low levels in serum (4th highest serum Ig) with a short plasma half-life due to sensitivity of the molecule. It exists as monomers and have a tail piece.IgD is expressed on the membranes of B cells when they leave the bone marrow and populate secondary lymphoid organs (Geisberger et al,2006). Its function is unclear, as it is not known to participate in themajor antibody effector mechanisms.However membrane-bound form of IgD is found primarily on B cells surface and serves as a receptor for Ag and also regulates B cell fate. As regard complement fixation, it does not fix complement(Riesbeck and Nordstrom,2006). 5- IgE :
tail piece (T- piece) which help the IgA to move across mucosa without degradation in secretions. There are two subclasses of IgA, IgA1 and IgA2, whose structures differ mainly in their hinge regions. They are IgA1 -Alpha 1 (α1) heavy chains and IgA2 -Alpha 2 (α2) heavy chains. IgA has a critical role in protection of mucosal surfaces from toxins, virus and bacteria by direct neutralization or by prevention of binding to the mucosal surface. Intracellular IgA may also be important in preventing bacterial or viral infection and/or pathogenesis. It can bind to Fc receptors on some cells as PMN cells and lymphocytes. It does not normally fix complement (unless aggregated)(Woof andMestecky, 2005). 4- IgD: It is found in low levels in serum (4th highest serum Ig) with a short plasma half-life due to sensitivity of the molecule. It exists as monomers and have a tail piece.IgD is expressed on the membranes of B cells when they leave the bone marrow and populate secondary lymphoid organs (Geisberger et al,2006). Its function is unclear, as it is not known to participate in themajor antibody effector mechanisms.However membrane-bound form of IgD is found primarily on B cells surface and serves as a receptor for Ag and also regulates B cell fate. As regard complement fixation, it does not fix complement(Riesbeck and Nordstrom,2006). 5- IgE :