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 interactions by recognition of at least one of its three identified counter-receptors, intercellular adhesion molecules 1 (ICAM-1), 2, and 3. The ICAM-1 molecule is expressed in an inducible-dependent manner by endothelial and epithelial cells, as well as by other cell types, including leukocytes. On the other hand, 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 distinct from those of ICAM-1 and ICAM-2. Interestingly, we have found that ICAM-3 is expressed by epidermal dendritic Langerhans cells as assessed by double immunostaining with antibodies specific for CD1. In contrast, staining of skin sections with anti-ICAM-1 and ICAM-2 antibodies showed an undetectable expression of these two molecules on Langerhans cells. However, CD1+ Langerhans cells localized in the paracortical 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-receptor in human resident epidermal Langerhans cells. ICAM-3 may have an important role in T-cell antigen stimulation driven by Langerhans cells during skin immune reactions.