Constant region of immunoglobulin heavy chains. Immunoglobulins, also known as antibodies, are membrane-bound orsecreted glycoproteins produced by B lymphocytes. In the recognitionphase of humoral immunity, the membrane-bound immunoglobulins serve asreceptors which, upon binding of a specific antigen, trigger the clonalexpansion and differentiation of B lymphocytes into immunoglobulins-secreting plasma cells. Secreted immunoglobulins mediate the effectorphase of humoral immunity, which results in the elimination of boundantigens. The antigen binding siteis formed by the variable domain of one heavy chain, together with thatof its associated light chain. Thus, each immunoglobulin has twoantigen binding sites with remarkable affinity for a particularantigen. The variable domains are assembled by a process called V- (D) -Jrearrangement and can then be subjected to somatic hypermutationswhich, after exposure to antigen and selection, allow affinitymaturation for a particular antigen. Ig alpha is the major immunoglobulin class in body secretions. [1-4]

ASPTSPKVFPLSLCSTQPDGNVVIACLVQGFFPQEPLSVTWSESGQGVTARNFPPSQDASGDLYTTSSQLTLPATQCLAGKSVTCHVKHYTNPSQDVTVPCPVPSTPPTPSPSTPPTPSPSCCHPRLSLHRPALEDLLLGSEANLTCTLTGLRDASGVTFTWTPSSGKSAVQGPPERDLCGCYSVSSVLPGCAEPWNHGKTFTCTAAYPESKTPLTATLSKSGNTFRPEVHLLPPPSEELALNELVTLTCLARGFSPKDVLVRWLQGSQELPREKYLTWASRQEPSQGTTTFAVTSILRVAAEDWKKGDTFSCMVGHEALPLAFTQKTIDRLAGKPTHVNVSVVMAEVDGTCY