DIFFERENTIAL PATTERNS OF EPIDERMAL LEUKOCYTE INFILTRATION IN PATCH TEST REACTIONS TO STRUCTURALLY UNRELATED CHEMICAL IRRITANTS

In previous studies, we showed that a number of aspects of the histopa thology of irritant contact dermatitis are profoundly influenced by th e chemical nature of the irritant applied. We report here that this ph enomenon also extends to the infiltration of leukocytes into the epide rmis. Healthy volunteers were patch tested with the following irritant s and their appropriate controls: benzalkonium chloride, sodium lauryl sulphate, croton oil, dithranol, nonanoic acid, and propylene glycol. After visually grading the intensity of the resulting inflammation, b iopsies were removed and the major phenotypic classes of leukocytes id entified immunocytochemically. Dermal and epidermal cell densities wer e determined, and the expression of several activation/proliferation a ntigens studied. We found a similar pattern of cellular infiltration i n the dermis of all irritant groups; the densities of most of the cell types rising in line with the intensity of inflammation. Within the e pidermis, however, there were marked differences in the patterns of ce llular infiltration between the irritant groups, leading to poorer cor relations between leukocyte density and visual grading. The greatest d isparity occurred between croton oil and nonanoic acid biopsies, the f ormer being characterized by the influx of large numbers of leukocytes , the latter showing remarkably little exocytosis. Infiltration of neu trophils occurred to varying degrees with all irritants, but a disprop ortionately large number were present in sodium lauryl sulphate biopsi es. All control groups showed a rise in CD4+ cells, with distilled wat er also producing increases in CD11c+ cells and neutrophils. A selecti ve influx of CD25+ cells occurred in the epidermis of both irritant an d control groups. our observations further highlight the heterogeneous nature of irritant contact dermatitis, and confirm previous findings that visually negative control patch tests show marked cellular reacti vity.