Separation of IgE from IgG subclasses using staphylococcal protein A.

When human serum was passed through a column of insolubilised protein A, IgE was not removed, but IgG sublasses 1,2 and 4 were retained. Protein A did not show a similar selectivity in its interaction with rat immunoglobulins. The separation of human IgE from the bulk of the IgG was used to examine the effect of IgG on IgE-mediated sensitization of lung tissue for histamine reslease. Removal of IgG led to a significant increase in histamine release, suggesting that homocytotropic IgG competes with IgE, for binding sites on mast cells.