Immune responses of cynomolgus monkeys to phthalic anhydride

Four groups of four Macaca fascicularis monkeys were administered 10 consecutive weekly subcutaneous injections of 2 mg aluminum hydroxide plus one of the following: 200 micrograms of phthalic anhydride (PA)-monkey serum albumin (PA-MSA, group 1); 200 micrograms of PA dissolved in ethanol-saline (EtOH-sal, group 2); 200 micrograms of MSA (group 3); or EtOH-sal alone (group 4). Direct intracutaneous tests to PA-MSA, PA-EtOH-sal, MSA, and EtOH-sal were applied at biweekly intervals throughout the course of the immunization. Serum-specific IgG to PA-MSA and specific IgE to PA-MSA were determined at 2-week intervals according to the ELISA and RAST methods, respectively. The prevalence of cutaneous sensitivity to PA-MSA in the PA-MSA-immunized group (group 1) was significantly greater after 4 and 6 (p less than 0.01) and 8 and 10 (p less than 0.05) weeks, compared with the other treatment groups. Significantly elevated (p less than 0.01) PA-MSA-specific IgG was also observed in monkeys in group 1 compared with the other treatment groups. No significant changes in PA-MSA RAST or total IgE were observed in any group during the study. These results indicate that parenteral sensitization to PA in subhuman primates requires the presence of new antigenic determinants formed by PA on protein carriers.