Leucocyte adhesion to cells in immune and inflammatory responses.

When activated under physiological or pathological conditions leucocytes transiently adhere to one another or to other cell types such as vascular endothelial cells. This adhesiveness is mediated by specific cell adhesion molecules (CAMs). There are two molecular pathways of leucocyte adhesion--the binding of CD11a-c/CD18 (Leu-CAM family) on leucocytes to CD54 (ICAM-1) on mononuclear leucocytes, fibroblasts, and epithelial and vascular endothelial cells, or of CD2 on T cells to CD58, a cell surface molecule found on a broad range of tissue cells. The adhesion process is essential for leucocyte-mediated cytotoxicity, phagocytosis, chemotaxis, and induction of lymphocyte proliferation and differentiation. It also participates in homing of lymphocytes into lymphoid organs and leucocyte migration from the vascular compartment to extravascular tissues. Leucocyte adhesion is thus a critical step in the development of immune and inflammatory responses. An inherited deficiency of the Leu-CAM family leads to recurrent bacterial infections, which can be fatal in early life, and lack of CAMs on Burkitt's lymphoma cells may enable these cells to escape immunesurveillance.