Background  Few authors have been attempting between mast cells and dermal dendrocytes interactions on urticaria.

Objective  To describe the extruded mast cell granules and dermal dendrocytes in drug-induced acute urticaria.

Methods  Seven patients with drug-induced acute urticaria were enrolled in the study. We token skin biopsies of urticaria lesion and perilesional skin. The 14 fragments collected were processed to immunogold electron microscopy using single stains to tryptase and FXIIIa, besides double immunogold labeling with both.

Results  Some sections demonstrated mast cells in degranulation process, both in anaphylactic and piecemeal degranulation types. After double immunogold staining, 10 nm (FXIIIa) and 15 nm (Tryptase) gold particles were present together over the granules in mast cells indicating that tryptase and FXIIIa are each localized within the granules of these cells. Interestingly, we found a strong evidence of than the exocytosed mast cell granules contents both FXIIIa and tryptase immunolabeled are phagocytized by dermal dendrocytes.

Conclusions  The current observations provide morphological evidence that the exocytosis-phagocytosis mechanisms of mast cell granules represents one pathophysiological example of mast cells-dermal dendrocytes interactions in urticaria.