Immunology Notes

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Western University
Microbiology and Immunology
Microbiology and Immunology 3300B
Rodney Dekoter

Immunology NotesOct 412 B cells are being generated in adults and they are rearranged through VDJ recombination This occurs in progenitor B cells prior to immune responses There are 5 types of Ig isotypes IgM IgD IgG IgE and IgA They differ in the amino acid sequence of constant heavy chains because the constant region is encoded for by different segments different exons The recombined VDJ codes for the variable region IgM and IgD are coexpressed by differential RNA splicing Both Igs are expressed on the surface of mature B cells but splicing causes either theheavy chain or theheavy chain to be formed In mature B cells transcription initiated at thepromoter extends through both C and C exons In one case splicing causes VDJ to be next to C In another a different pattern of splicing causes VDJ to be next to C Transmembrane versus secreted forms of Igs are coexpressed by differential RNA splicing Each heavy chain C gene has two exons that encode the transmembrane region and cytoplasmic tail of the transmembrane form and a secretioncoding sequence that encodes the carboxy terminus of the secreted form Each Ig can be produced as transmembrane or secreted Different exons code for the different types Occurs at the level of RNA splicing not DNA recombination The J chain is required for dimeric IgA and pentameric IgM The J chain is a polypeptide chain and it links the Fc regions of molecules through disulphide bonds IgG1 is the major form of Ig in the body Its concentration of antibodies is the highest in the serum It is involved in the classical pathway of complement activation placental transfer fetus is protected from infection by antibodies transferred from mother binding to macrophage and phagocyte Fc receptors and reactivity with staph protein A The rest of the IgGs have the same functions IgM is the first Ig that is made before it is switched to other types It is involved in the classical pathway of complement activation IgA has two forms IgA1 and IgA2 IgE is present i
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