Two further exceptions illustrate the complexity of helminth-immune interactions at the single cell type level: eosinophils promote infection with Trichinella spiralis [39] while mast cell degranulation during filarial larval invasion of the skin may facilitate infection by raising vascular permeability; CCL17−/− mice fail to inhibit local mast cell responses and are more susceptible [47]. The gene discussed is CCL17; the disease is infection.