Cutaneous lymphocyte-associated antigen (CLA), which plays a key part in skin homing of human CD4⁺ memory T cells via CLA/E-selectin binding, is upregulated by IL-12 and downregulated by IL-4. Although α1,3-fucosyltransferase VII is essential for synthesis of the CLA carbohydrate epitope, little is known about how the CLA expression is regulated by a number of glycosyltransferases. A 6 wk long-term culture for the in vitro differentiation of naïve Th cells to memory Th1 cells was employed. By repeated activation in the presence of IL-12, naïve T cells differentiated into memory Th1 cells, resulting in the upregulation of CLA expression. The switching of cytokine from IL-12 to IL-4 at three cycles resulted in a marked downregulation of CLA. The transcript levels of 16 glycosyltransferases and P-selectin glycoprotein ligand-1, all considered to be potentially involved in CLA synthesis, were determined after each cycle. The level of CLA expression was well correlated with the amounts of α1,3-fucosyltransferase VII and β1,4-galactosyltransferase I. Both were upregulated by IL-12 and downregulated by IL-4. In particular, α1,3-fucosyltransferase VII levels decreased markedly in the presence of IL-4. P-selectin glycoprotein ligand-1 and Core 2 β1,6-N-acetylglucosaminyltransferase were progressively up-regulated by repeated IL-12 stimulation, but they were not downregulated by IL-4. The transcript levels of some genes examined were constitutive without any correlation to CLA expression. These results suggest that the level of CLA expression is determined by α1,3-fucosyltransferase VII and β1,4-galactosyltransferase I, the other enzymes merely participating in the synthesis of CLA. In peripheral blood mononuclear cells, IL-12 and IL-4 profoundly upregulated and downregulated the α1,3-fucosyltransferase VII transcripts, respectively, but not the β1,4-galactosyltransferase I ones, within only 2 h of in vitro culture. This suggested that α1,3-fucosyltransferase VII is transcriptionally regulated directly by IL-12 and IL-4.