Modulation of host immune responses by Fasciola hepatica: responses by peripheral lymphocytes to mitogens during liver fluke infections of sheep.

Fasciola hepatica infections of lambs (250 or 500 metacercariae) were shown to alter the proliferative responses of peripheral blood lymphocytes (whole blood culture) to mitogens at specific times postinfection (PI). Responses to concanavalin A (Con A) were significantly suppressed at weeks 4, 8, 10, and 11 PI whereas suppressed responses to phytohemagglutinin (PHA) occurred at weeks 4, 10, 11, and 16 PI. Only on weeks 4 and 6 PI were responses to pokeweed mitogen (PWM) suppressed. The fluke-induced modulation of responses appeared to be related more to specific phases of infection rather than to worm burdens.