Protective immunity and mast cell and eosinophil responses in mice infested with larval Haemaphysalis longicornis ticks

WBB6F1 -+- /+ mice were infested with larval Haemaphysalis longicornis ticks twice at an interval of 14 days: apparent resistance against ticks was expressed in the second infestation. The first infestation induced degranula-tion of a small number of mast cells at the feeding sites within 6 days, and resulted in two-fold increases of mast cell numbers on day 14 with a significant elevation of total immunoglobulin E (IgE) levels in sera and high proportion of IgE-bound mast cells. The second infestation resulted in the intensive degranulation of the increased mast cells at the feeding sites. Eosinophils infiltrated into the feeding sites of ticks: the second infestation led to a greater maximal level of the infiltrating eosinophils. These data suggest that the resistance against larval H. longicornis ticks in mice may be expressed as a result of immediate hypersensitivity and many eosinophils infiltrating from the blood to the feeding sites might contribute to the tick rejection.