Do eosinophils have a role in the killing of helminth parasites?

Eosinophils have been shown to be potent effector cells for the killing of helminth parasites in in vitro cultures. However, an in vivo role for eosin ophils has been more difficult to establish. Early data showed close associ ations between eosinophils and damaged or dead parasites in histological se ctions, and significant correlations between resistance to parasites and th e capacity to induce eosinophilia after infection. However, more recent stu dies, using mice that have reduced or increased eosinophil levels through t argeting of the eosinophil-specific cytokine interleukin 5, have not unanim ously supported an in vivo role for eosinophils in resistance to parasites. Here, Els Meeusen and Adam Balic review these studies and suggest a major role for the innate immune response in unnatural mouse-parasite models to e xplain some of the findings. They conclude that the data so far are consist ent with a role for eosinophils in the killing of infective larval stages, but not adults, of most helminth parasites.