Tick resistance in mast cell-deficient mice: histological studies.

Mast cell-deficient W/Wv mice and their mast cell-sufficient +/+ genetic controls were allowed to undergo three successive infestations with Dermacentor variabilis larvae. Histological examination of the skin of infected mice revealed large dermal accumulations of eosinophils and smaller numbers of neutrophils. The numbers of both eosinophils and neutrophils increased significantly in W/Wv and +/+ mice during secondary and tertiary infestations. Mast cell numbers were also found to increase in the skin of +/+ mice during tertiary infestations. Resistance, as measured by decreased larval engorged weights on day 5 of each infestation, was acquired by both strains of mice.