DISTRIBUTION OF ICAM-3-BEARING CELLS IN NORMAL HUMAN TISSUES - EXPRESSION OF A NOVEL COUNTER-RECEPTOR FOR LFA-1 IN EPIDERMAL LANGERHANS CELLS

The LFA-1 integrin mediates its function in leukocyte intercellular in teractions by recognition of at least one of its three identified coun ter-receptors, intercellular adhesion molecules 1 (ICAM-1), 2, and 3. The IC4M-1 molecule is expressed in an inducible-dependent manner by e ndothelial and epithelial cells, as well as by other cell types, inclu ding leukocytes. On the other band, ICAM-2 is constitutively expressed mainly by endothelial cells. We have studied the tissue distribution of the ICAM-3 molecule by immunohistochemical staining of lymphoid and nonlymphoid organs. Only cells from the leukocyte lineage were found bearing the ICAM-3 antigen, showing a pattern of expression clearly di stinct from those of ICAM-1 and ICAM-2. Interestingly, we have found t hat ICAM-3 is expressed by epidermal dendritic Langerhans cells as ass essed by double immuno-staining with antibodies specific for CD1. In c ontrast, staining of skin sections with anti-ICAM-1 and ICAM-2 antibod ies showed an undetectable expression of these two molecules on Langer hans cells. However, CD1+ Langerhans cells localized in the paracortic al area of dermatopathic lymph nodes expressed both ICAM-1 and ICAM-3 antigens. Our results indicate that ICAM-3 is the main LFA-1 counter-r eceptor in human resident epidermal Langerhans cells. ICAM-3 may have an important role in T-cell antigen stimulation driven by Langerhans c ells during skin immune reactions.