Influence ofDermacentor andersoniinfestation on lymphocyte responsiveness to mitogens

Lymphocytes from randomly bred guinea-pigs, each infested with two female and one male Dermacentor andersoni, showed significantly less in vitro responsiveness to the T-lymphocyte mitogens concanavalin A and phytohaemagglutinin, while stimulation by the B-lymphocyte mitogen Escherichia coli lipopolysaccharide was unimpaired. Reduced in vitro reactivity occurred after an initial five-day infestation, as well as after a second, similar infestation, which was initiated following a seven-day tick-free period. These results provide evidence that ixodid tick infestation induces a variable, but significant, degree of reduced host immune responsiveness. The importance of these findings in terms of the expression of host resistance to tick infestation and the transmission of tick-borne pathogens is discussed.