Mast cell participation during the elicitation of murine allergic contact hypersensitivity

In order to evaluate mast cell participation in allergic contact hypersensitivity (ACH), BALB/c mice were sensitized with 0.1% trinitrochlorobenzene (TNCB). Immediately before challenge and at 1, 1.5, 2, 4, 6, 8, 12, 24, and 48 h after challenge with 1% TNCB, groups of animals had ear thickness measured, had blood collected for histamine determinations, and had both ears removed for histologic evaluation of mast cells. The increase in ear swelling was triphasic with peak increases at 1.5 h (14.3 +/- 1.6 X 10(-2) mm; mean +/- SEM), 8 h (19.9 +/- 1.8 X 10(-2) mm), and 24 h (30.2 +/- 2.9 X 10(-2) mm). A triphasic pattern of increased serum histamine was noted at 1-4 h (117% over control levels), at 12 h (131%), and at 48 h (133%). Examination of the tissue specimens from challenged animals showed modest (1+) degranulation of mast cells between 1 and 6 h with extensive (2+) degranulation at 12 h. In addition, hypogranulated mast cells were evident between 1 and 6 h, at 24 h, and at 48 h. There were no statistically significant differences in mast cell numbers at any time. Neither platelets nor other formed elements of the blood contributed to the increased blood histamine levels. These data show that mast cells are activated in a triphasic pattern during ACH, and thus suggest both early and late roles for the mast cell and its products in the evolution of ACH.