Induction of type I hypersensitivity in guinea pigs after inhalation of phthalic anhydride

Guinea pigs were exposed through inhalation to phthalic anhydride (PA) dust at 0.5, 1.0, and 5.0 mg/m3, 3 hours/day for 5 consecutive days. Inhalation challenge with aerosolized phthalic anhydride-guinea pig serum albumin (PA-GPSA) conjugate elicited immediate-onset respiratory reactions in animals exposed to all three levels of dust. Inhalation challenge of a subgroup of animals with phthalic anhydride dust did not elicit an immediate response, as measured by changes in respiratory frequency and plethysmograph pressure. Serologic studies showed that these animals had allergic IgG1a antibody to PA-GPSA. There was a dose-dependent increase in specific IgG antibody activity, as measured by ELISA. Animals exposed to and challenged with 5.0 mg/m3 PA dust had significant numbers of hemorrhagic lung foci. Those animals with the greatest number of foci had high IgG antibody activity to PA, as measured by ELISA. This study showed that exposure to levels of PA dust as low as 0.5 mg/m3, below the current threshold limit value of 6.0 mg/m3, can sensitize animals to produce allergic antibody.