The purpose of this study is to clarify signal transduction of expression of the intercellular adhesion molecule-1 (ICAM-1) via CD40-CD40 ligand in salivary glands of patients with Sjögren's syndrome (SS). We used cultured salivary gland epithelial cells (SG cells) from 15 SS patients and 8 controls obtained by labial minor salivary gland biopsy. First, ICAM-1 expression was determined with reverse transcriptase-polymerase chain reaction and flow cytometry in the presence or absence of soluble CD40L (sCD40L). Next, SG cells were transfected with plasmids of pGL1.3-Luc inserted with promoter region of ICAM-1, pGL1.3kB(-)-Luc mutated in nuclear factor kappa-B (NF-kappaB) binding site of pGL1.3-Luc and pNF-kappaB-Luc by lipofection method. Luciferase activity of the cells was measured in the presence or absence of sCD40L or sCD40L and an NF-kappaB inhibitor, pyrrolidine dithiocarbamate (PDTC). Finally NF-kappaB family proteins of cell nuclear extracts were determined. ICAM-1 expression was significantly enhanced with sCD40L at the mRNA and protein level. Activity of pNF-kappaB-Luc and pGL1.3-Luc was significantly elevated by stimulation with sCD40L and suppressed by PDTC. NF-kappaB p50 protein level was elevated by stimulation with sCD40L and suppressed by PDTC. Our results suggest that sCD40L enhances the ICAM-1 expression by activation of NF-kappaB p50 in the SS SG cells.