Cutaneous and systemic responses during primary and challenge infestationsof sheep with the sheep scab mite, Psoroptes ovis

Lesional area was estimated and lesional mast cells and eosinophils were co unted during primary and challenge infestations of sheep with Psoroptes ovi s. In addition, circulating basophils and eosinophils and serum P. ovis-spe cific immunoglobulin IgE antibody were quantified. Expansion of lesional ar ea was significantly less and serum IgE titres significantly greater in cha llenge than primary infestations. Lesional mast cell hyperplasia and massiv e eosinophil infiltration accompanied by raised titres of P. ovis antigen-s pecific IgE antibody were compatible with an IgE-mediated Type-1 allergic r eaction while detection of lesional basophils was suggestive of cutaneous b asophil hypersensitivity. The temporal pattern of lesional mastocytosis and eosinophil infiltration and the role of these cells and serum IgE in the i mmune response is discussed.