Reaginic Activity Associated with Immunoglobulins Other than IgE¹ Free

Absorption studies using antisera to the Fc portion of the IgG molecule isolated from cord sera demonstrated that human reaginic activity belongs to more than one class of immunoglobulin. The data indicated that at least two types of protein carried reaginic activity, one of which was not an IgE immunoglobulin and probably was IgG. The non-IgE type had an intradermal half-life and latency period similar to that of IgE, and was destroyed by heating to 56°C for 4 hr.