Immune responsiveness of the bovine host to repeated low-level infestations withDermacentor andersoni

Abstract

The effects of low level infestations with adult Dermacentor andersoni (Stiles) on the immune responsiveness of Bos taurus cows and calves were examined. Exposure regimen consisted of one to four ten-day infestations, each with ten female and five male ticks. Tick feedings were separated by ten-day tick-free periods. Antibody responsiveness to infestation differed for cows and calves, calves uniformly displaying precipitating antibodies to D. andersoni salivary gland antigen (SGA) after all infestations. Most of the cows displayed precipitating antibodies before and after the first infestation, but by the end of the second infestation most cows had lost detectable precipitating antibodies to SGA. All tick-exposed cows and calves gave significant immediate and delayed reactions when skin-tested with SGA. Peripheral blood lymphocytes derived from cows and calves at the termination of a third and fourth infestation reacted in vitro in an antigen-specific manner to SGA, indicating the presence of an antigen-reactive cell population. All this time in vitro responsiveness to the mitogen, phytohaemagglutinin, was significantly reduced. This observation suggested a degree of immunosuppression resultant from tick infestation. Low level exposure to D. andersoni infestation stimulated a number of host immune responses, which parallel those observed when guinea-pigs were infested with D. andersoni larvae.