Local immune response to experimental Fasciola hepatica infection in sheep

Macrophages, eosinophils, neutrophils and lymphocyte subpopulations (OvCD5+, OvCD4+, OvCD8+, OvWC1+ and Ig(+)) were identified in sections of hepatic tissue and hepatic lymph nodes from sheep experimentaly injected with F. hepatica and necropsied 14, 28, 42 or 56 days post infection. The migratory tunnels produced by juvenile flukes appeared as local areas of necrosis surrounded by infiltrating inflammatory cells, particularly numerous macrophages, eosinophils and OvCD4(+) lymphocytes. In addition, B lymphocyte proliferation was observed in hepatic lymph nodes and in hepatic portal tracts. Only three juvenile flukes were identified in the sections. They where partially in contact with healthy tissue and partially with neutrophils, macrophages and eosinophils; they were covered by IgM. Host-parasite interactions resulting from immune response regulation by helper T lymphocytes and from immune evasion by the parasite are discussed.