SUMMARYDirected migration of lymphocytes from blood into lymph nodes and organ-associated lymphatic tissue, also referred to as homing, is initiated by T-cell adhesion to specialized high endothelial cells of postcapillary vessels. Here, we demonstrate that selective signal transduction pathways specifically modulate the expression of the cutaneous lymphocyte antigen (CLA), the putative skin-homing receptor, during naive to memory transition of CD4+ T cells in vitro. The results show that the expression of CLA is strongly induced by activation via CD2 [TI 1.1 + T11.2 monoclonal antibodies (mAb)]. Addition of transforming growth factor-fil (TGF-PI), interleukin-6 (IL-6), and, to a lesser extent, IL-2 further enhanced the generation of CLA+ T cells, whereas the induction of this antigen was markedly inhibited by IL-4. Periodic restimulation via CD2 and long-term culture of activated cells in the presence of IL-2 and TGF-BI resulted in stable expression of CLA during a culture period of more than 100 days. In contrast, activation of naive CD4+ T cells via CD3, CD28 or by mitogens induced a rapid naive to memory phenotype transition but a much lower percentage of CLA+ T cells showing only weak expression of the antigen. Furthermore, activation of purified CD4+ memory T cells by CD2 strongly induced expression of activation-related antigens CD25 and HLA-DR, but failed to up-regulate CLA expression. Our results show that primary stimulation conditions highly modulate the development of skin-associated T cells and indicate a new functional role for costimulatory adhesion pathways in regulating the expression of molecules associated with T-cell homing.