Mechanisms of eosinophilia in BALB/c-nu/+ and congenitally athymic BALB/c-nu/nu mice infected with Toxocara canis.

We studied the mechanism of eosinophilia in BALB/c-nu/+ (nu/+) and BALB/c-nu/nu (nu/nu) mice infected with Toxocara canis. Eosinophilia with two peaks on days 11 and 21 of infection was observed in infected nu/+ mice, and with a peak on day 11 in nu/nu mice. Interleukin-5 (IL-5) mRNA was expressed on day 5 of infection in the lung and spleen of nu/+ mice and in the lung of nu/nu mice, but not in the spleen of nu/nu mice. Large numbers of eosinophils and lymphocytes infiltrated the lung of both mice 1 week after infection. The number of larvae in the lung was the largest on day 5. Anti-IL-5 monoclonal antibody (mAb) treatment completely inhibited eosinophilia of both mice, with no change of larval distribution. Administration of anti-CD4 or anti-CD3 mAb markedly reduced the second peak of eosinophilia on day 21 of infection in nu/+ mice, and slightly reduced the first peak of eosinophilia on day 11 in both mice. Anti-CD8 mAb had no effect on the eosinophilia. These results suggest that eosinophilia in both mice is caused by IL-5, and that IL-5 is produced by cells other than CD4+ T cells, in addition to CD4+ T cells.