Adhesion molecules on the plasma membrane of epidermal cells. IV. Immunolocalization of the intercellular adhesion molecule-1 (ICAM-1, CD54) on the cell surface of a small subpopulation of keratinocytes freshly isolated from normal human epidermis.
The intercellular adhesion molecule-1 (ICAM-1) is a cell membrane glycoprotein displaying a pivvtal role in cell-cell interactions in the immune system, and is a ligand for LFA-1, which is expressed on leukocytes. ICAM-1 is expressed in different cell types, including epithelial cells in a number of organs; the universal feature on all these cells is ICAM-1 induction from very low ICAM-1 constitutive levels on unstimulated resting cells to very high ICAM-1 levels triggered by mediators released at sites of inflammation. Therefore, since a strong expression of ICAM-1 on keratinocyte (KC) surface was recently demonstrated in various inflammatory skin lesions, in this investigation we asked whether very low ICAM-1 levels might be present on the plasma membrane of unstimulated KC in normal skin. Crude epidermal cell suspensions, freshly isolated from normal human skin, were immunolabeled by anti-ICAM-1 monoclonal antibody and stained by two highly sensitive ultrastructural detection systems, namely, the immunogold (5-nm-sized particles) method and the immunogold-silver-enhancement method. The quantitative analysis of 1000 KC scrutinized under the electron microscope revealed that 17.2% KC were ICAM-1-positive, although a density per KC section (midplane) of merely 18.92 +/- 13.02 5 nm-sized particles was scored (n = 100), indicating that the amounts of ICAM-1 moieties on this KC subset are presumably low. The ICAM-1 expression on a subset of KC in normal skin might account for the trafficking to and from normal epidermis of LFA-1-positive cells, including migrating Langerhans cells and occasional leukocytes.