Studies on the mechanism of immunoglobulin binding to red cells.

The red cell uptake of IgG on the basis of absorption experiments appears to be due to two populations of IgG molecules. One population is readily absorbable by red cells. The quantity of this type of IgG varies from preparation to preparation and appears to depend on the method used for preparing the IgG. It appears that this population of IgG molecules represents denatured or aggregated IgG, although no direct evidence of aggregation was obtained in these studies. The other population of red cell absorbable IgG appears to be proportional to the IgG concentration and cannot be depleted by successive red cell absorption of the IgG solution. A similar pattern of reactivity with red cells was found using [I] IgM. Labelled subunits of IgM and fragments of IgG (Fab and Fc), differed from IgG and IgM in that they did not contain a population consisting of a variable quantity of readily absorbable molecules.