Antibody to interleukin 5 prevents blood and tissue eosinophilia but not liver trapping in murine larval toxocariasis.

Mice previously sensitized by infective-stage larvae of the canine nematode, Toxocara canis, trap large numbers of challenge larvae within the liver; trapped larvae are found within eosinophilic granulomas. To investigate the role of eosinophils in this phenomenon we examined larval trapping in mice depleted of blood and tissue eosinophils by treatment with a monoclonal antibody (MoAb) (TRFK-5) produced against recombinant murine interleukin 5 (rmIL-5). Control mice received either an isotype-matched control MoAb or PBS. On day 0 test mice were given a sensitization dose of 125 infective T. canis eggs. Test and challenge control mice received 500 infective eggs on day 28. All mice were killed on day 42 and larval numbers within the liver were determined. Liver samples were also collected for histopathological and morphometric examination. When compared to test mice treated with PBS or the isotype control, the level of circulating eosinophils in anti-IL-5-treated test mice was reduced by 94-96% on days 14 and 27, 99% on day 35, and 100% on day 42; the level of tissue eosinophils within liver granulomas on day 42 was reduced by 92-95%. The total area of inflammation within the liver was similar among all test groups. However, the highly eosinophilic infiltrates, present in control sections, were replaced in anti-IL-5-treated mice by lymphocytes, macrophages, and foreign-body giant cells. No difference was found in larval trapping between antibody-treated groups. These findings suggest that the eosinophil is not necessary for liver trapping in murine larval toxocariasis.