Characterization of a factor from rat serum with blocking activity in the passive cutaneous anaphylactic reaction.

A blocking factor (BF) was obtained from normal and rat reaginic serum which inhibited the passive cutaneous anaphylactic (PCA) reaction of mouse and rat IgE in rat skin. Several chromatographic procedures on DEAE- and CM-cellulose at various pH values were compared in an attempt to obtain BF with high activity. BF-containing fractions after DEAE chromatography at pH 5,4 revealed two components on SDS-polyacrylamide gel: one at 50,000-60,000 and the other at 65,000-70,000 daltons. The latter component was also obtained when normal or rat reaginic serum was adsorbed on Sepharose anti rat IgG. The eluate inhibited the PCA reaction and demonstrated two bands on SDS-polyacrylamide gel, one at 150,000 (IgG) and another at 65,000-70,000 daltons. Purified IgG and rat albumin did not inhibit the PCA reaction. Antisera against BF were obtained with the component at 65,000-70,000 daltons. Anti-BF revealed a specificity for two bands in the cathodal position when assayed against normal rat serum; one of which was IgG. Anti-BF recognized one component in the DEAE fraction when analyzed against the DEAE fraction which contained blocking activity. BF is immunologically distinct from IgG. After immunoadsorption of normal or rat reaginic serum on Sepharose anti-BF columns, an eluate was obtained which showed blocking activity in the PCA reaction and two components on SDS-polyacrylamide gel, one at 150,000 and the other at 65,000-70,000 daltons. Evaluation of blocking factor by isoelectric focussing obtained after various procedures revealed an isoelectric point of 4.7. BF shows dual functions: it inhibits and at high dilutions also enhances the PCA reaction. It is suggested that this factor has a modulatory role in the allergic disease process.