Preferential adherence of T lymphocytes and neutrophils to psoriatic epidermis

T lymphocytes and neutrophils accumulate in psoriatic epidermis. To determine whether the epidermis plays an active role in this process through the production of cellular adhesion factors, leucocyte adherence to lesional psoriasis was compared with normal skin in a modified frozen-section adhesion assay. Lymphocyte and neutrophil suspensions were prepared by standard Ficoll-Hypaque techniques from peripheral blood of normal volunteers and overlaid on to glutaraldehyde-fixed 8-microns cryostat sections of skin. Adhesion of phorbol ester-activated T lymphocytes to the epidermis was significantly greater in psoriasis compared with normal skin (P < 0.01). Adhesion was absent (a) at 7 degrees C, (b) in the presence of EDTA and (c) in the absence of lymphocyte activation. Immunostaining demonstrated that all adherent lymphocytes were CD3+ve (i.e. T cells). Likewise, neutrophils adhered more prominently to psoriatic epidermis. Adhesion was most prominent at the tips of dermal papillae, corresponding to areas of maximal intercellular adhesion molecule-1 (ICAM-1) expression. Both neutrophils and lymphocytes adhered to dermal papillary vascular endothelium. These studies provide functional data that psoriatic epidermal cells are actively involved in leucocyte adherence. The distribution of adhesion suggests that both ICAM-1-dependent and independent mechanisms are involved.