Evidence and mechanisms of immunosuppression in tick infestations

The abundance and ubiquity of ticks from ancient times long ago suggested that they have eluded host immunity. In the last 15 years, several authors have demonstrated suppression of the Th1 responses (cell-mediated immunity), and sometimes the Th2 responses (humoral immunity), subsequent to tick infestations in laboratory and natural models. Although the mechanisms to produce suppression ale nor well-defined yet, evidences for antigenic competition, lymphocyte cylotoxicity, presence of immuno-inhibiting substances ill the saliva, and existence of modulators of cytokines in salivary extracts have been reported. Management of tick-induced immunosuppression is essential to replace tick control by acaricide application with more environmentally sound vaccination. (C) 1999 Elsevier Science B.V. All rights reserved.