Antibody classes

Type I allergic reactions are inappropriate immune responses to an allergen with preferential synthesis of immunoglobulin E (IgE), a special antibody class, which binds to mast cells and basophilic granulocytes via Fee receptors. Binding of the allergen to the cell-bound IgE initiates the rapid release of allergic mediators, most prominently histamine, and the de novo synthesis of arachidonic acid metabolites and cytokines, which are responsible for the clinical symptoms. 

Antibody classes In mammals, there are five classes of antibodies (also known as immunoglobulins IgG, IgA, IgM, IgE and IgD). Each immunoglobulin class differs in their heavy chain constant domains (see Fig. 1.2) and consequently in its biological properties. For immunoassays, two immuno-glubulin classes are of importance - IgG and IgM. 

Antibody isotypes Differences in the amino acid sequence and disulfide bonding patterns of the heavy chain in antibody classes give rise to antibody subclasses (also referred to as isotypes). For instance, mouse IgG antibodies are divided into four isotypes IgGl, IgG2, IgG2a, and IgG3. 

Species Antibody class Protein A Affinity to Protein G Protein L Thiophilic medium... 

Antibody class. The major proportion of the primary response is made up of IgM, whereas the secondary response consists almost entirely of IgG. 

It has been known for many years that during the course of a typical immune response, different antibody classes are produced IgM is found early in the response and IgG later (e.g. Bauer and Stavitsky, 1961 Uhr and Finkelstein, 1963). In a typical heterogeneous polyclonal response, the IgM and IgG antibodies appear to have similar specificity, but the structural relationship of the binding sites (in modern terms, the V regions) associated with these different classes cannot easily be evaluated. However, a crucial insight into the relationship among V regions of different antibody classes was provided by Todd s observation (1963) that rabbit IgG and IgM express the same a-locus allotypic determinants. 

Two different forms of light chains also exist. Antibody molecules in any of the antibody classes or sub-classes can have either two k light chains or two A. light chains. Unlike the different heavy chains described above, no difference in biological function between k and A light chains is known. 

Class switching When the complete heavy chain gene shown in Fig. 4 is transcribed, it generates a heavy chain for an IgM antibody since it is always the first C segment after the recombined VDJ (in this case CJ that is transcribed. To switch to making a heavy chain for a different antibody class, say IgA, the lymphocyte DNA has to undergo yet another recombination event that moves Ca next to... 

IL-4 Helper T-cells B cells Stimulation of proliferation and maturation antibody class switching... 

Isotype The process where antibody class expression changes as in the rearrangement... 

B.B., Crit. Rev. Immunol. 24, 297-320, 2004 Fiset, P.O., Cameron, L., and Hamid, Q., Local isotype switching to IgE in airway mucosa, J. Allergy Clin. Immunol. 116, 233-236, 2005 Min, I.M. and Seising, E., Antibody class switch recombination roles for switch seqences and mismatch repair proteins, Adv. Immunol. 87, 297-328, 2005 Apian, P.D., Causes of oncogenic chromosomal translocation. Trends Genet. 22, 46-55, 2006. 

Exposure to a specific antigen causes clonal expansion of all B cells capable of reacting with the multiple epitopes present on the antigen. Thus, the immune response to the entire antigen results in the production of antibodies by several clones of B cells. The resultant mixture of antibodies present in the serum is called a polyclonal antibody. In addition, because an animal is naturally exposed to a host of other antigens in its environment, its serum also contains antibodies produced by clones specific for each of these antigens. Therefore a polyclonal antibody preparation obtained from an animal is a mixture of many distinct antibody classes, only some of which are specific for the antigen used in experimental immunization. 

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