Specific IgE to castor bean (Ricinus communis) pollen in the sera of clinically sensitive patients to seeds

Human sensitization to castor bean seeds in occupational workers and people living close to oil processing factories has been acknowledged for a long time. In view of the crossreactivity among different plant parts of the same species, we studied crossreactivity between seeds of castor bean and its pollen at the molecular level. Sera from 26 seed-positive atopics, when analyzed for ELISA aganist seed and pollen extracts of castor bean, showed binding with both seed and pollen extracts, but binding was stronger with seed extracts as compared to pollen. ELISA inhibition revealed partial similarity as pollen extract could not achieve 90% inhibition even at 100 ug/ml, and remained the same alter protein concentrations of 40 ug/ml. Antigenic extracts of seeds and pollen separated into 12 and 20 fractions on SDS-PAGE, respectively. The 26 sera studied for specific IgE binding to different fractions of seed and pollen extracts showed IgE binding in 17 and 16 cases respectively, but with weak binding to pollen fractions. The crossreactivity was confirmed with pooled sera by blot inhibition. Seed antigen completely inhibited the sera for specific IgE at 10 mg/ml protein while pollen antigen showed only partial inhibition. Crossreactivity and presence of common epitopes between seed and pollen extracts are confirmed.