Inhibition and Reversal of Aggregation of Immunoglobulin G by Freezing.

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Abstract
Solutions of IgG (about 1 g/100 ml) from normal subjects form between 10 and 50% aggregates (10 S, 12 S and precipitation) on repeated freezing and thawing. Aggregation was effectively prevented by glycine in concentrations of about 0.1 mole/1, both at pH 7.0 and 3.0. After the IgG-glycine solution dialyzed against a glycine-free buffer the IgG again formed aggregates upon freezing. Aggregation did not occur in IgG solutions containing plasmin. Components smaller than 7 S were formed. Traces of aggregates were formed in a 5% NaCl-solution, and the 7 S component became unusually inhomogeneous. Proline, serine, arginine, albumin and fibrinogen retarded the aggregation. The amount of aggregate remained unchanged when iodo-acetamide was added. An increase of percentage of aggregates was noted when IgG was dissolved in phosphate buffer containing HAc [acetic acid] or in phosphate buffer at pH 3.0. When IgG was dissolved in acetate buffer at pH 3.0, the solution became so viscous after freezing that its composition could not be studied. Glycine buffer at pH 3.0 had the ability to convert the aggregate to smaller molecules. A homogeneous 7 S peak persisted after the solution had been dialyzed against phosphate buffer at pH 7.0. Also in urea the aggregated molecules were broken down into smaller components but reaggregation occurred in urea-free phosphate buffer. In glycine buffer at pH 5.8, part of the aggregate was broken down to 7 S molecules; but after dialysis against glycine-free buffer the effect was negligible. The NaCl did not affect the aggregated IgG molecules.

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