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 histopathology of irritant contact dermatitis are profoundly influenced by the chemical nature of the irritant applied. We report here that this phenomenon also extends to the infiltration of leukocytes into the epidermis. Healthy volunteers were patch tested with the following irritants 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, biopsies were removed and the major phenotypic classes of leukocytes identified immunocytochemically. Dermal and epidermal cell densities were determined, and the expression of several activation/proliferation antigens studied. We found a similar pattern of cellular infiltration in the dermis of all irritant groups; the densities of most of the cell types rising in line with the intensity of inflammation. Within the epidermis, however, there were marked differences in the patterns of cellular infiltration between the irritant groups, leading to poorer correlations between leukocyte density and visual grading. The greatest disparity occurred between croton oil and nonanoic acid biopsies, the former being characterized by the influx of large numbers of leukocytes, the latter showing remarkably little exocytosis. Infiltration of neutrophils occurred to varying degrees with all irritants, but a disproportionately large number were present in sodium lauryl sulphate biopsies. All control groups showed a rise in CD4+ cells, with distilled water also producing increases in CD11c+ cells and neutrophils. A selective influx of CD25+ cells occurred in the epidermis of both irritant and 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 reactivity.