Immunoglobulins and the Isotype Switch

During the primary response of a normal individual, B cells produce antibodies of the IgM type. Several hours after the onset of IgM production, stimulated by the presence of interferon^ (IFN-7), IgG-producing B cells swing into action. Eventually, blood serum concentration of IgG antibodies increases above that of IgM, but as long as the antigen is present in the body, both IgM and IgG antibodies continue to be produced. Upon complete antigen removal, B cell stimulation is shut off and the remaining antibodies are catabolised and broken down. Should the same pathogen with the same antigens attempt to reinvade the body, it will stimulate a faster and mn

Total mn

Total

Time

1st Ag

2nd Ag

Figure 12.1

Isotype switch during primary and secondary immune response. The concentrations are plotted on a logarithmic scale. The time units are not specified because the kinetics differ somewhat with type of antigen, administration route, species, or strain of animal (adapted from [24]).

Time

1st Ag

2nd Ag

Figure 12.1

Isotype switch during primary and secondary immune response. The concentrations are plotted on a logarithmic scale. The time units are not specified because the kinetics differ somewhat with type of antigen, administration route, species, or strain of animal (adapted from [24]).

stronger antibody production (secondary response in Figure 12.1). This time the IgG antibody producing cells proliferate and release IgG just as quickly as the IgM producing cells. The above pattern of the immune reaction in a normal individual is altered in hypersensitive subjects, mainly by IgE antibodies being produced instead of IgG antibodies. This isotype switch takes place in stimulated B cells in the presence of certain cytokines produced by T helper cells [24]. A "normal" isotype switch to IgG occurs if the concentration of interleukin-12 (IL-12) is relatively high, whereas a switch to IgE is dependent on the concentration of IL-4. The problem in having high levels of IgE serum is that they bind to mast cells and basophils through the Fc receptor on the cell membrane, thus sensitising these cells. A subsequent exposure to the same allergen induces cross-linking of IgE-bound molecules on sensitised cells. Cross-linking is a term indicating a complex series of events which signal a cell to degranulate and release active mediators, such as histamine, serotonin, proteases, eosinophil chemotactic factor (ECF-A), neutrophil chemotactic factor (NCF-A), platelet-activating factor, leukotrienes, prostaglandinis, etc. Finally, the presence of these active molecules provoke a sequence of events, culminating in the symptoms of hypersensitivity. For example, the leukotrienes mediate broncho-constriction, increased vascular permeability, and mucus production (as seen in asthmatics) [24,25].

How To Bolster Your Immune System

How To Bolster Your Immune System

All Natural Immune Boosters Proven To Fight Infection, Disease And More. Discover A Natural, Safe Effective Way To Boost Your Immune System Using Ingredients From Your Kitchen Cupboard. The only common sense, no holds barred guide to hit the market today no gimmicks, no pills, just old fashioned common sense remedies to cure colds, influenza, viral infections and more.

Get My Free Audio Book


Post a comment