KERATINOCYTES RESIDENT IN NORMAL HUMAN SKIN CONSTITUTIVELY EXPRESS, AT LOW-LEVELS, THE INTERCELLULAR-ADHESION MOLECULE-1 - AN IN-SITU IMMUNOELECTRONMICROSCOPY STUDY

The expression of intercellular adhesion molecule-1 (ICAM-1) on kerati nocytes (KC) was previously demonstrated in biopsies from various infl ammatory skin lesions. KC were, however, found virtually ICAM-1 negati ve, in normal skin, when the same immunocytochemical techniques were e mployed. By contrast, epithelial cells resident in different organs co nstitutively express ICAM-1, albeit weakly. The aim of the present stu dy was to use an immunostaining system more sensitive than the convent ional immunocytochemistry, namely the in situ immunogold labelling of ultracryosections, to investigate the constitutive ICAM-1 expression b y resting KC in normal skin, in vivo. The semiquantitative analysis pe rformed on 500 resident KC, visualized within tissue ultracryosections of normal human skin, revealed that gold granules were present along the cell membrane in a small percentage (146%) of resident KC. The den sity of gold particles (10 nm sized) observed on the cell surface per KC section was as scarce as 13.72 +/- 4.6 (mean rt standard deviation) , although highly significant when compared with controls (P < 0.005). This indicates the presumably low expression of ICAM-1 moieties on th e plasma membrane of this I(C subset. This ICAM-1 expression could be important in modulating the trafficking to and from normal epidermis o f migrating Langerhans cells and occasional leucocytes. The fact that the ICAM-1 expression on KC in normal skin is limited can be considere d favourable, because it can account for the prevention of inappropria te KC/leucocyte interactions in the resting cutaneous environment.