Suppression of passive cutaneous anaphylactic reaction by a human serum factor

The capacity of human serum to inhibit the IgE-mediated passive cutaneous anaphylactic reaction in mouse was established. The active fraction was isolated by ammonium sulfate precipitation (33-40% saturation). Its molecular weight, as estimated by gel filtration, was found to be 42-66 kd. Affinity chromatography on lectins showed affinity of the factor for concanavalin A but not for peanut agglutinin. Treatment of the active fraction with exoglycosidases showed that mannose in the factor is essential for its biological activity. When the inhibitory factor was separated on mouse IgE-coated nitrocellulose membranes, its molecular weight estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was 64.5 kd. The factor is thermolabile at 55 degrees C. In a population study approximately 28% of human sera showed the presence of this factor.