The different immunoglobulin subclasses are as follows:
1. IgM. This is the first type of antibody to be secretedduring the primary response and they serve as receptors on the lymphocyte surface. These antibodies also promote agglutination reactions (causing antigen-containing particles to stick together, or agglutinate).
2. IgG. This is the major form of antibody in the blood plasma and is secreted in a secondary response.
3. IgD. These antibodies serve as receptors for antigens on the B cell surface. Their other functions are
unknown.
4. IgA. This is the major form of antibody in external secretions, such as saliva and mother’s milk.
5. IgE. This form of antibodies promotes the release of histamine and other agents that aid in attacking a
pathogen. Unfortunately, they sometimes trigger a full-blown response when a harmless antigen enters
the body producing allergic symptoms, such as those of hay fever.
Each B cell has on its surface about 100,000 IgM or IgD receptors. Unlike the receptors on T cells, which
bind only to antigens presented by certain cells, B receptors can bind to free antigens. This provokes a primary response in which antibodies of the IgM class are secreted, and also stimulates cell division and clonal expansion. Upon subsequent exposure, the plasma cells secrete large amounts of antibodies that are generally of the IgGclass. Although plasma cells live only a few days, theyproduce a vast number of antibodies. In fact, antibodies constitute about 20% by weight of the total protein in blood plasma. Production of IgG antibodies peaks after about three weeks . When IgM (and to a lesser extent IgG) antibodies bind to antigens on a cell, they cause the aggregation of complement proteins. As we mentioned earlier, these proteins form a pore that pierces the plasma membrane of the infected cell , allowing water to enter and causing the cell to burst. In contrast, when IgG antibodies bind to antigens on a cell, they serve as markers that stimulate phagocytosis by macrophages. Because certain complement proteins attract phagocytic cells, activation of complement is generally accompanied by increased phagocytosis. Notice that antibodies don’t kill invading pathogens directly; rather, they cause destruction of the pathogens by activating the complement system and by targeting the pathogen for attack by phagocytic cells.
1. IgM. This is the first type of antibody to be secretedduring the primary response and they serve as receptors on the lymphocyte surface. These antibodies also promote agglutination reactions (causing antigen-containing particles to stick together, or agglutinate).
2. IgG. This is the major form of antibody in the blood plasma and is secreted in a secondary response.
3. IgD. These antibodies serve as receptors for antigens on the B cell surface. Their other functions are
unknown.
4. IgA. This is the major form of antibody in external secretions, such as saliva and mother’s milk.
5. IgE. This form of antibodies promotes the release of histamine and other agents that aid in attacking a
pathogen. Unfortunately, they sometimes trigger a full-blown response when a harmless antigen enters
the body producing allergic symptoms, such as those of hay fever.
Each B cell has on its surface about 100,000 IgM or IgD receptors. Unlike the receptors on T cells, which
bind only to antigens presented by certain cells, B receptors can bind to free antigens. This provokes a primary response in which antibodies of the IgM class are secreted, and also stimulates cell division and clonal expansion. Upon subsequent exposure, the plasma cells secrete large amounts of antibodies that are generally of the IgGclass. Although plasma cells live only a few days, theyproduce a vast number of antibodies. In fact, antibodies constitute about 20% by weight of the total protein in blood plasma. Production of IgG antibodies peaks after about three weeks . When IgM (and to a lesser extent IgG) antibodies bind to antigens on a cell, they cause the aggregation of complement proteins. As we mentioned earlier, these proteins form a pore that pierces the plasma membrane of the infected cell , allowing water to enter and causing the cell to burst. In contrast, when IgG antibodies bind to antigens on a cell, they serve as markers that stimulate phagocytosis by macrophages. Because certain complement proteins attract phagocytic cells, activation of complement is generally accompanied by increased phagocytosis. Notice that antibodies don’t kill invading pathogens directly; rather, they cause destruction of the pathogens by activating the complement system and by targeting the pathogen for attack by phagocytic cells.
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