T cell subset involvement in immune responses to Fasciola hepatica infection in cattle

The lymphocyte response to F. hepatica during a primary infection in cattle was analysed to define the role of T cell subsets in the immune response. Blood lymphocytes were isolated from eight cattle infected with F. hepatica via trickle infection over a ten-day period and from two non-infected cont rols. CD4(+), CD8(+) and gamma delta(+) T cells were depleted from whole ly mphocyte populations by magnetic bead depletion. Lymphocytes from infected animals demonstrated a transient, but marked elevation in responsiveness to F hepatica antigen between weeks 3 and 8 post-infection. Responses were at tenuated by depletion of CD4(+) and CD8(+) T cells during this period. Depl etion of gamma delta(+) T cells attenuated antigen responses at one time po int only, and at an earlier stage post-infection than when alpha beta(+) T cells were depleted. Responses to antigen correlated positively with both h epatic fluke burden and with the degree of hepatic damage. This suggests th at the cellular immune response was not protective. Antigen responses in ga mma delta(+) T cell-depleted populations were also associated with post-mor tem fluke burden and with hepatic damage, This suggests that gamma delta(+) T cells are involved in down regulating alpha beta(+) lymphocytes which ma y have a role in a non-protective or immunopathological immune responses.