T cell-dependent mast cell degranulation and release of serotonin in murine delayed-type hypersensitivity.

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Abstract
Serotonin (5-hydroxytryptamine) (5-HT) release by local tissue mast cells may be required for the elicitation of delayed-type hypersensitivity (DTH) in mice. Light microscopic radioautographs from animals treated with [3H]5-HT indicate that local mast cells released 5-HT between 6 and 18 h during DTH evolution. Ultrastructural examination of mast cells revealed surface activation, indicated by surface filopodia extension, and degranulation by fusion and exocytosis. Light microscopic and EM studies of the postcapillary venule endothelium at sites of DTH revealed the development of gaps between adjacent cells. The development of gaps permitted extravasation of tracers that was abolished by depletion or antagonism of 5-HT. Thus, mast cells degranulated and released 5-HT in DTH, and this 5-HT acted on local vessels. Recipients of nonadherent, non-Ig-bearing sensitized lymphocytes also demonstrated similar mast cell degranulation and endothelial gap formation. This indicated that mast cell degranulation and 5-HT release in murine DTH were probably T cell dependent.