Acquired resistance to ticks. IV. Skin reactivity and in vitro lymphocyte responsiveness to salivary gland antigen.

Guinea-pigs developed resistance to the ixodid tick, , after one infestation. Resistance was characterized by guinea-pigs allowing significantly fewer larvae (10–20%) to engorge during a second infestation than during an initial infestation (90–99%). Data reported here further confirm the immunological nature of guinea-pig resistance to larvae and indicate the presence of a cell-mediated immune component to the resistance. An antigen isolated from the salivary glands of adult female was shown to stimulate delayed skin reactivity when administered intradermally to tick-resistant guinea-pigs. Salivary gland antigen (SGA) initiated lymphocyte blastogenesis when added to cultures of lymph node cells from tick-resistant hosts. Antigen-specific responsiveness of lymphocytes to SGA occurred over a period of from 2 to 4 days after the termination of an initial infestation with tick larvae until the termination of a second infestation. Basophils first appeared at tick attachment sites at the time when antigen-specific lymphocyte responsiveness was first significant. Peak responsiveness occurred 24 h after the initiation of a second laval infestation at a time when large numbers of basophils were attracted to the tick attachment site. Evidence is also presented to suggest that tick infestation might induce a degree of immunosuppression in the host.