Lewis triple response is caused due to:: (A) Histamine, (B) Axon reflex, (C) Injury to endothelium, (D) Increased permeability
Answer is A. Lewis triple response is caused due to Histamine When histamine is injected intradermally it causes the triple response consisting of: Red spot: Due to capillary dilatation. Wheal: Due to exudation of fluid from capillaries and venules. Flare: Redness in the surrounding area due to aeriolar dilation mediated by axon reflex. A, 'Triple response' elicited by firm stroking of skin of forearm with a pencil. B, Diagrammatic view of microscopic features of triple response of the skin