The relation between skin histamine concentration, histamine sensitivity, and the resistance of cattle to the tick, Boophilus microplus.

Cattle with different degrees of resistance to Boophilus microplus have responses to tick allergen which correlate with their resistance level. The total amount of histamine in the skin also correlates with both resistance and the immediate hypersensitivity reactions, but the sensitivity to injected histamine does not. Treatment with the antihistamine drug mepyramine maleate suppresses the cutaneous hypersensitivity reactions. The results suggest that the main pharmacologically active agent in these reactions is histamine, and that the total amount of it available locally in the skin may have a role in the resistance to this parasite.