Immunoglobulins cell-binding properties

When the red blood cells are removed from whole blood, and the resulting plasma is allowed to clot, the fibrinogen may be removed to yield serum. Serum contains a variety of proteins, some of which are called globulins because their solubility properties are different from the other serum proteins. Antibodies are a subclass of serum globulins that possess selective binding properties. Antibodies are also called immunoglobulins (Ig). 

Acute and chronic viral hepatitis are associated with a myriad of extrahep-atic tissue injuries, not all of which are directly related to the cytotoxic effects of HBV and HCV [35, 36], These include skin rashes and urticarial reactions in about 5% of patients with viral hepatitis [37 10], We investigated the possibility that protein Fv purified from patients suffering from HCV infection can activate basophils and mast cells purified from human lung and skin tissues. We found that protein Fv purified from stool extracts of patients with HCV infection induced histamine release from human basophils [32, 41]. Interestingly, the histamine-releasing activity of protein Fv was superimposible with its immunoglobulin-binding property (fig. 2). 

Most clinical isolates of S. aureus synthesize protein A, a cell wall protein endowed with unique immunoglobulin-binding properties. Protein A has a classical site that binds the Fey of IgG [60], and an alternative site that binds the Fab portion of 15-50% of human polyclonal IgG, IgM, IgA, and IgE [61]. 

Many bacteria possess specific properties because specific proteins or glycoproteins are situated on the cell surface. Staphylococcus aureus is an example of bacteria carrying specific molecules - called protein A (40,41). This protein has specific binding properties since it bincTs immunoglobulin subgroups I, II and IV via their F fragments. Protein A, purified as well as when bound to the Cell walls of killed cells, have been used in radio immunoassay (42,43) and in enzyme immunoassay (44). 

Protein A (PA) is a cell wall component produced by over 98% of the strains of Staphylococcus aureus that have been tested. It was reported first by Verwey, then rediscovered by Jensen nearly two decades later Its name emphasizes the chemical class, since PA originally was believed to be a polysaccharide, but shown later to be a protein with little or no carbohydrate. The outsmnding functional property of PA is its ability to bind specifically to the Fc region of immunoglobulin molecules, especially... 

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