Evaluating the quality of immunoglobulin G preparations for intravenous therapy.

The major function of immunoglobulins is recognition of the antigen that has caused their formation with subsequent antigen binding and removal through antigen nonspecific recognition systems of the body. Such clearance for detrimental antigens depends on a complex system of now clearly characterized single features of the immunoglobulin molecule, such as antigen-binding capacity, viral neutralization, complement activation, fixation to receptors on the reticuloendothelial system, and maintenance of an optimal half-life in circulation before antigen removal. When gamma-globulins are used therapeutically, the producer must choose a purification procedure that aims at fully maintaining these features. In fact, isolation of any protein from its natural plasma protein environment may induce subtle losses of function that do not appear when such variables as molecular weight or subunit size are applied as the only quality criteria.