The effect of ablation of eosinophils on immediate-type hypersensitivity reactions

The effect of ablation of eosinophils on hypersensitivity reactions in guinea-pigs was tested by administration of rabbit antiserum to the eosinophil (AES) and by administration of glucocorticoids. Both AES and methylprednisolone ablated eosinophils from the blood and peritoneal cavity of test animals. Neither administration of AES nor methylprednisolone, however, altered passive cutaneous or systemic anaphylactic reactions when compared to reactions occurring in control animals treated with normal rabbit serum (NRS). Also there was no consistent effect of AES on the intensity of the Arthus reaction. The effect of ablation of eosinophils on histamine release in the passively sensitized peritoneal cavity of the guinea-pig was also tested. In five experiments a significant reduction in histamine release was seen in AES-treated animals. Ablation of eosinophils by cortisone acetate also resulted in a marked reduction in the quantity of histamine released into the peritoneal cavity following passive sensitization and antigen challenge. Histamine release following intraperitoneal injection of compound 48/80 was not affected by either the prior administration of AES or cortisone acetate, suggesting that the stores of histamine were not depleted by these agents. Overall these results suggest that eosinophils do not play a prominent role in initial expression of immediate-type hypersensitivity reactions where the density of these cells in tissues is low. When present in larger numbers, however, eosinophils may contribute to histamine release in immediate-type reactions.