Differential localization of ICAM-1 and HLA-DR expression on epidermal basal surface in mycosis fungoides and lichenoid reaction.

Scanning electron microscopy with immunogold labeling revealed that epidermal keratinocytes expressed ICAM-1 (intercellular adhesion molecule-1) and HLA-DR molecules on their surfaces in patterns that differed in mycosis fungoides (MF) and lichenoid reaction (LR). ICAM-1 molecules, visualized as deposits of gold particle, were visualized as clusters adjacent to the junctions interconnecting the keratinocytes of MF lesions. LFA-1 (leukocyte function-associated antigen-1) molecules were seen as granules on the surfaces of all infiltrates, most of which also expressed ICAM-1. HLA-DR molecules were seen continuously along the borders of the individual keratinocytes, thus producing a cobblestone appearance on the epidermal undersurface. In contrast, ICAM-1 and HLA-DR were found only sparsely on the undersurface of the epidermis from LR. These findings may help to explain the differing histological features of MF and LR: ICAM-1 molecules present on the intercellular junctions of MF epidermis lead the LFA-1-bearing cells to migrate into the interspaces, thus producing epidermotropism. These cells aggregate by means of co-expressed ICAM-1 to thus produce Pautrier's microabscess. In LR, the minimal expression of ICAm-1 on the epidermal undersurface leaves most infiltrates within the dermis, thus producing a band-like infiltrate.