Expression of free radicals by peritoneal cells of sheep during the early stages of Fasciola hepatica infection

BACKGROUND: The majority of vaccination studies against infection with F. hepatica in a natural host have been conducted at the late stage of the infection when the host's immune response is already immunomodulated by the parasite towards a Th2 non-protective response. This study was aimed at analysing the dynamic of the cell populations present in peritoneal liquid and the production of free radicals by the peritoneal leukocytes in infected and vaccinated sheep with recombinant cathepsin L1 of F. hepatica (rFhCL1) in early stages of the infection. METHODS: Forty-five sheep were divided into three groups: Group 1 remained as negative control (n = 5), Group 2 (n = 20) was challenged with F. hepatica and Group 3 (n = 20) was vaccinated with rFhCL1 and challenged with F. hepatica. After the slaughtering, peritoneal lavages were carried out at 1, 3, 9 and 18 days post-infection (dpi) to isolate peritoneal cell populations. Flow cytometry was conducted to assess levels of hydrogen peroxide (H(2)O(2)) and nitric oxide (NO). RESULTS: There was a significant increase in the total number of leukocytes at 9 and 18 dpi in infected and vaccinated groups. Production of H(2)O(2) was significantly increased in peritoneal granulocytes in both infected and vaccinated groups. Production of nitric oxide showed a significant rise in the granulocytes and monocytes/macrophages in infected and vaccinated sheep. The NO production by granulocytes at 3 and 9 dpi was significantly higher in the vaccinated than in the infected animals. CONCLUSIONS: Experimental infection induced an increase in the total number of leukocytes within the abdominal cavity at 9 and 18 dpi, being more noticeable in vaccinated animals. Production of H(2)O(2) occurred mainly in granulocytes of vaccinated and infected animals. Production of NO was incremented in vaccinated and non-vaccinated animals in all peritoneal cells. Vaccinated animals produced significant higher level of H(2)O(2) and NO than infected animals.