Immunoglobulin constant region

Abbreviations MBN, myoglobin MGN, myogen MHN, myohemerythrin RUB, mbredoxin ICG, immunoglobulin constant region IGV, immunoglobulin variable region PBN, prealbumin SDM, superoxide dismutase CON, conconavalin A CHT, chymotrypsin INS, insulin PTI, pancreatic trypsin inhibitor CB5, cytochrome b5 ... 

Biologicals. Figure 3 Fusion protein construction combination of the molecular component of interest with the constant region (Fc) of an antibody molecule, usually immunoglobulin (lg)G1 Fc, imparts the Fc function on to the molecularcomponentfortherapeutic use. The example given is ofCTLA4-lg, derivatives of which have shown clinical efficacy in the treatment of rheumatoid arthritis and transplant rejection. 

The constant regions of the immunoglobulin molecules, particularly the C 2 and 0 3 (and C 4 of IgM and IgE), which constitute the Fc fragment, are responsible for the class-specific effector functions of the different immunoglobulin molecules (Table 50-7, bottom part), eg, complement fixation or transplacental passage. 

Figure 1.10. Generalised structure of the variable and constant domains within antibodies. The variable regions (dark shading) of either the light or heavy chains are indicated as VL or VH, respectively. The light chains also possess one constant region (CL), whereas the heavy chains possess either three or four constant regions (Ch)-Ch4). depending upon the class of immunoglobulin (see text for details).

Figure 1.13. Schematic representation of an IgA molecule. Each IgA molecule comprises immunoglobulin molecules joined to each other via a J chain. The heavy chains possess three constant regions (Co1 Cce). The secretory chain (SC) is secreted by epithelial cells and binds to the IgA dimer via disulphide bonds (indicated by wriggly lines).

In summary, for all the immunoglobulin molecules within one class, the amino acid sequence in the constant region of the chains is identical the massive number of different molecules within each class is accounted for by the amino acid sequences in the variable and hypervariable regions of both the light and heavy chains. 

Lefranc, M. R, Hammarstrom, L., Smith, C. I. E., and Lefranc, G., Gene deletions in the human immunoglobulin heavy chain constant region locus Molecular and immunological analysis. Immunol. Rev. 2, 265-281 (1991). 

Molecular studies over the years, including sequence analysis of immunoglobulins and their genes, revealed that amino-acid sequences in constant regions of the H chains found in Fc fragments are the same in individual subjects within the same species but different among species. The sequence differences between species are... 

Matthyssens, G., Rabbitts, T.H. (1980). Structure and multiplicity of genes for the human immunoglobulin heavy chain constant region. Pmc. Natl. Acad. Sci. USA, 77, 6561-6565. 

There are five different types of heavy chains, which correspond with five different classes of antibodies. The constant region of the heavy chain is identical in all antibodies of the same class. The classes of the immunoglobulin molecules differ based on the Fc region of the heavy chain, which are responsible for the different functions performed by each class. Thus the constant region confers on each class of antibody its effector function. 

---