THE LYMPHOCYTE ASSOCIATED LFA - 1 , LFA - 3 MOLECULES " Receptors FUNCTION - CD 2 , and Cell Adhesion of the Immune System

Cell adhesion molecules are thought to play an important role in guiding cell migration and localization in the development of the embryo and in organogenesis. In the immune system, cell adhesion molecules enhance the efficiency of specific receptor-dependent lymphocyte-accessory cell and lymphocyte-target cell interactions ; they are also important in leukocyteendothelial cell interactions and lymphocyte recirculation. Recent studies with monoclonal antibodies (MAb) that perturb antigen-receptor-dependent T-lymphocyte functions have defined a number of cell surface molecules that are associated with lymphocyte function (lymphocyte functio~ associated or LFA antigens) (Table 1). The antigens LFA-1, CD2, LFA3, CD8, and CD4 appear to enhance antigen-specific functions by acting as cell adhesion molecules. Further studies have shown that the LFA-1, CD2, and LFA-3 molecules are also important in antigen-independent T-lymphocyte adherence and function and that the LFA-1 molecule is important in the adherence and function of essentially all leukocyte cell types. This review focuses on LFA-1, CD2, and LFA-3. The role of CD4 and CD8 is reviewed by Littman in this volume. We discuss (a) the contributions of LFA-1, CD2, and LFA-3 to antigen-dependent and antigen-