Lewis Triple Response• Described by sir Thomas Lewis in 1924.

• Lewis triple response is the characteristic 3 part response that develops when a line is made by a pointed object (a key) on the skin. It is produced due to the release of histamine from the mast cells.

• Trauma may release an antigen that interacts with the membrane-bound immunoglobulin E of mast cells, which release inflammatory mediators, particularly histamine, into the tissues. This causes small blood vessels to leak, allowing fluid to accumulate in the skin.

Inflammatory Response

Components of the Triple Response

1.Red reaction: red line (transient local vasodilation due to histamine), appears in few seconds.

2.Wheal: localized edema in the region of the redline (increased capillary permeability and exudation of fluid from capillaries and venules due to histamine release), appears in 1 min.

3.Flare: spreading redness extending beyond the red line (due to axon reflex), appears slowly.

- Three cell types – smooth muscle in the microcirculation – endothelium: capillary or venule – sensory nerve endings

Receptor types

Type Location Function

H1 Smooth m., endothelium, CNS

Bronchoconstriction, Contraction of GIT, VasodilatationIncreased capillary permeability leading to edemaPain and itch

H2 Parietal cells, vascular smooth m.

Vasodilatation, gastric acid secretion

H3 CNS Modulate the release of other neurotransmitters

H4 Basophils, BM, Thymus, spleen

Chemotaxis

Subgroups of Histamine Receptor Blockers

What will occur with

Antihistamine OR

Local Anesthetics?