Inhibition of drug-induced eosinophilia by cyclosporin A.

Administration of cyclophosphamide to Sprague-Dawley rats 2 days before immunization with ovalbumin in complete Freund's adjuvant resulted in a striking blood, bone marrow, and tissue eosinophilia. The number of circulating eosinophils reached a maximum (50-fold increase above normal) 2 weeks after immunization, and eosinophils were also prominent in bone marrow, lymph nodes (paracortical areas), spleen (white and red pulp), and liver. The eosinophilia could be inhibited by daily oral administration of cyclosporin A (CsA), although its effect was dependent both on the duration of treatment and on the dosage of CsA. A similar, inhibitory action of CsA was demonstrated with respect to methotrexate-induced eosinophilia. This experimental model may prove useful in the study of factors regulating eosinophil production and in examining the prospective value of CsA in the treatment of conditions where eosinophils play a central role.