During T cell activation, TCRs cluster at the center of the T cell-antigen-presenting cell interface forming the central supramolecular activation cluster. Although it has been suggested that sphingolipid- and cholesterol-rich microdomains, termed lipid rafts, form platforms for the regulation and transduction of TCR signals, an actual role for membrane sphingomyelin (SM), a key component of lipid rafts, has not been reported. After cloning a gene responsible for SM synthesis, sphingomyelin synthase (SMS) 1, we established a SM-knockdown cell line (Jurkat-SMS1/kd) by transfection of SMS1-short-interfering RNA into Jurkat T cells, which is deficient in membrane expression of SM. Upon CD3 stimulation, expression of CD69 (the earliest leukocyte activation antigen), activation-induced cell adhesion and proliferation as well as TCR clustering was severely impaired in Jurkat-SMS1/kd cells. CD3-induced tyrosine phosphorylation and association of linker for activation of T cell with ZAP-70 and Grb2 and phosphorylation of protein kinase C (PKC) were also severely impaired in Jurkat-SMS1/kd cells. Finally, translocation of TCR, ZAP-70 and PKC into lipid rafts was markedly decreased in Jurkat-SMS1/kd cells. These findings indicate that membrane SM is crucial for TCR signal transduction, leading to full T cell activation through lipid raft function.

Leukocyte adhesion and trafficking at the endothelium requires both adhesion molecules and chemotactic factors. Fractalkine (CX3C) is a unique chemokine, and is expressed on tumor necrosis factor-alpha- and interleukin-1-activated endothelial cells (ECs). Fractalkine receptor, CX3CR1, is expressed on NK cells, monocytes, and some portion of CD4- and CD8-positive T cells. Interactions between fractalkine and CX3CR1 can mediate not only chemotaxis, but also cell adhesion in the absence of substrates for other adhesion molecules. Furthermore, fractalkine activates NK cells, leading to increased cytotoxicity and interferon-gamma production. Recently, accumulating evidence has shown that fractalkine is involved in the pathogenesis of rheumatoid arthritis and allied conditions. This review examines new concepts underlying fractalkine-mediated leukocyte migration and tissue damage, focusing primarily on the pathophysiological roles of fractalkine in rheumatic diseases.

Leukocyte adhesion and trafficking at the endothelium requires both adhesion molecules and chemotactic factors. Fractalkine (CX3C) is a unique chemokine, and is expressed on tumor necrosis factor-alpha- and interleukin-1-activated endothelial cells (ECs). Fractalkine receptor, CX3CR1, is expressed on NK cells, monocytes, and some portion of CD4- and CD8-positive T cells. Interactions between fractalkine and CX3CR1 can mediate not only chemotaxis, but also cell adhesion in the absence of substrates for other adhesion molecules. Furthermore, fractalkine activates NK cells, leading to increased cytotoxicity and interferon-gamma production. Recently, accumulating evidence has shown that fractalkine is involved in the pathogenesis of rheumatoid arthritis and allied conditions. This review examines new concepts underlying fractalkine-mediated leukocyte migration and tissue damage, focusing primarily on the pathophysiological roles of fractalkine in rheumatic diseases.

Serum titers of antibody to Epstein-Barr virus (EBV) viral capsid antigen (VCA) have been positively correlated with malignancies of lymphoid proliferation, such as Burkitt's lymphoma and Hodgkin's lymphoma. We have constructed a phage display combinatorial antibody Fab library from a patient with marginal zone B cell lymphoma associated with Sjögren's syndrome and carrying high serum anti-EBV-VCA IgG titer. Fab fragments were selected by panning against EBV-VCA protein coated onto ELISA plates, and selected Fab clones were characterized by ELISA, western blotting (WB), indirect immunofluorescence assay and immunohistochemistry. We have established two Fab clones, Fab-aVCA1 and Fab-aVCA21, which specifically recognize EBV-VCA by ELISA and WB. Inhibition ELISA competition showed that both clones could significantly reduce the binding of specific anti-EBV-VCA mAb to its relevant proteins. Furthermore, these two Fab clones could localize VCA protein in the EBV-positive P3HR1 and Daudi cell lines, as well as in tissue samples from patients with EBV-infected lymphoid malignancies. These results indicate that our two Fab clones are novel human mAbs specific for EBV-VCA protein and may have potential benefits for development of novel diagnostic and therapeutic approaches in EBV-related lymphoid malignancies.