IgG1--as the only subclass of human serum IgG--spontaneously undergoes O2(-)-induced, noncovalent self-aggregation...

An apparent gradual decrease of IgG1 serum levels of up to 40% occurs within 48 h of storage at room temperature. The effect does not concern any other IgG subclass, and is more pronounced in sera of smokers. A linear correlation was found between the extent of this "storage effect" and the initial concentration of IgG1, which rules out an enzymatic process following Michaelis-Menten kinetics. PAGE and Western blots of density gradient separated serum proteins revealed the presence of noncovalent self aggregates of IgG1 in stored sera. Addition of superoxide dismutase prevented both the formation of aggregates as well as the decay of IgG1 values. It is concluded that the instability of IgG1 is due to an enhanced propensity of this molecule to form self-aggregates, whereby O2(-)-radicals play a functional role. This mechanism, however, is not relevant to a previously detected selective decrease of relative IgG1 levels in sera of patients afflicted with malignant diseases of various tissue origin.