Acquired resistance of guinea pigs to Dermacentor andersoni mediated by humoral factors.

Humoral and cell-mediated immune resistance to tick infestation has been documented in many host-parasite relationships. This study examines passive transfer of resistance to Dermacentor andersoni expressed by recipients of serum pools derived from guinea pigs that had acquired resistance through experimental infestation. Recipients of sera from high titer adult-infested animals expressed resistance evidenced by reduced engorgement weights, histological changes at tick attachment sites, and tick antigen-reactive cytophilic antibody. Recipients of lower titer sera from nymph-infested guinea pigs did not show significant reductions in engorgement weights but did exhibit inflammatory reactions at tick attachment sites similar to those of high titer sera recipients. This study, together with previous findings, suggests that immature instars of D. andersoni may not be as effective as adult ticks in stimulating sufficient humoral responses to convey biological resistance to naive recipients, and it underscores the influence the route of serum administration can have on passive transfer studies.