Background Mosquito bites frequently cause wealing and delayed papules which appear within a few hours after the bites and may persist for several days. Cetirizine is an effective drug against mosquito bites by decreasing wealing and also the size and pruritus of the delayed bite papules.
Objectives To characterize inflammatory cells in the delayed mosquito-bite lesions, and to study the effect of cetirizine on the inflammatory cell response.
Methods Twenty-six mosquito-bite sensitive subjects received cetirizine 20 mg (14 subjects) or placebo (12 subjects) in a double-blind fashion. Aedes aegypti-bites were given on a forearm and serial punch biopsies were taken at 2-, 6- and 24 h after the bite exposure, Eosinophils, neutrophils, mast cells, mononuclear cells and T- helper (CD4+) and suppressor (CD8+) lymphocytes were counted from dermal infiltrates.
Results Eosinophils and neutrophiis were found already in 2-h bite lesions. Moreover, the number of mononuclear and CD4+ cells increased significantly (P < 0,01) from 2- to 24-h bite lesions. Unexpectedly, the overall numbers of eosinophils (P < 0.05), mononuclear cells (P < 0.01) and CD4f cells (P < 0.01) were significantly higher in the cetirizine-treated subjects compared with the placebo-treated subjects.
Conclusions The results suggest that the inflammatory cell response in the delayed mosquito-bite lesions is similar to that occurring in allergic late-phase responses, i.e. an early influx of eosinophils, neutrophils and subsequent accumalation of CD4+ lymphocytes. The reason for the high numbers of eosinophils and CD4+ cells in the cetirizine-treated subjects is not known.