THE ONTOGENY OF ADHESION MOLECULES EXPRESSED ON THE VASCULAR ENDOTHELIUM OF THE DEVELOPING HUMAN SKIN

One of the important functions of adhesion molecules is to regulate th e trafficking of lymphocytes and other leucocytes between the differen t organs and tissues of the body. These molecules are expressed on bot h the endothelial cells and the leucocytes, enabling them to adhere to one another and ultimately lead to extravasation of the leucocytes fr om the circulation into the surrounding tissue. P and E-selectin promo te 'rolling' of leucocytes along the blood vessel walls, whereas ICAM- 1 and VCAM-1 mediate subsequent firm adhesion, thus committing the leu cocytes to extravasation. We have investigated the expression of the a bove endothelial adhesion molecules in relation to the developing derm al vasculature of fetal skin using histology and immunocytochemistry. This study showed that already at 11 wk of gestation some dermal vesse ls expressed P-selectin and ICAM-1. However, by 18 wk these molecules were identified on a significant number of vessels, including small ca pillaries supplying the forming dermal pegs. In contrast, E-selectin a nd VCAM-1 molecules were rarely seen in all specimens examined. Our re sults show that even at 11 wk of gestation, the fetal skin has a mecha nism in place for circulating leucocytes to extravasate and provide pr imitive immunosurveillance. Furthermore, the similarities between the distribution of P-selectin and ICAM-1 in the 18 wk fetal skin and in t he normal adult skin were striking. These findings may shed light on o ur understanding of how the fetus detects and reacts to infections and may, in the future, lead to advances in the management of some intrau terine infections.