Cimetidine-induced augmentation of allergic contact hypersensitivity reactions in mice

BALB/c mice were treated with cimetidine (100 mg/kg) or saline, intraperitoneally, twice daily, from days 0-2 or days 7-9 after sensitization with 0.1%, 2,4,6-trinitro-1-chlorobenzene (TNCB) on day 0. On day 7, the mice were challenged with 1% TNCB to one ear. Ear swelling responses (as an index of sensitization), serum histamine levels, and biopsy specimens of challenged ears were evaluated in groups of cimetidine- or saline-treated mice at 0, 0.5, 1, 1.5, 2, 4, 6, 8, 12, 24, and 48 h after challenge. Additional controls included mice injected with saline or cimetidine and challenged with, but not sensitized to, TNCB (irritant controls). Treatment with cimetidine during the induction but not the elicitation of allergic contact hypersensitivity (ACH) produced a significant enhancement of the response throughout the first 48 h. There was no effect of cimetidine on antigen-presenting cells within the epidermis which might account for this enhancement. Similarly, no difference in mast cell morphology or serum histamine levels between cimetidine- and saline-treated groups was observed. Histologically, the cimetidine-treated animals showed a more intense cellular infiltrate, which was most noticeable at 24 to 48 h, at which time numerous subcorneal and perifollicular neutrophilic abscesses were observed. To further investigate the mechanism of action of cimetidine, mice were injected with cyclophosphamide (150 mg/kg) 2 d prior to sensitization. Mice treated with cyclophosphamide alone or in combination with cimetidine showed no additive or synergistic effect upon the ear swelling response. We conclude that enhancement of ACH by cimetidine is independent of any effect on mast cells or antigen-presenting cells, but may relate to a cimetidine-induced inhibition of the induction of T-suppressor cells at the time of sensitization.