Tetraspanins, the hepatitis C virus and cell migration

The function of CD81 on mature T cells is unknown. We employ a system in which B cells present superantigen to autologous T cells and find that anti-CD81 promotes T cell-B cell collaboration. Anti-CD81 induces T cell-B cell adhesion of PBL which is partially mediated by LFA-1. CD81 engagement promotes LFA-1 dependent T cell activation, IL-2 production and proliferation. The antibody 5A6 was uniquely potent in exerting these effects compared to another antibody to CD81 or to antibodies that react with other tetraspanins expressed on T cells, anti-CD53 or anti-CD82. CD81-derived signals rapidly induce high avidity LFA-1 as measured by cell binding to recombinant ICAM-3 coated fluorescent microspheres or by cell adhesion to ICAM-3 coated plastic. 5A6 activation of LFA-1 does not expose the high affinity conformation epitope recognized by mAb 24.; CD81 is a receptor for the Hepatitis C virus envelope glycoprotein E2. Structural analysis of CD81 has enabled the synthesis of small molecules designed to mimic the space and hydrophobic features of the E2 binding site on CD81. Utilizing a novel bis-imidazole scaffold a series of over 100 compounds has been synthesized. Seven related, imidazole-based compounds were identified which inhibit binding of HCV-E2 to CD81. The inhibitory compounds have no short-term effect on cellular expression of CD81 or other tetraspanins, do not disrupt CD81 associations with other cell surface proteins and bind reversibly to HCV-E2. These results provide an important proof of concept that CD81-based mimics can disrupt binding of HCV-E2 to CD81.; Unrelated to CD81, we demonstrate that formyl peptide receptors are expressed by normal human lung and skin fibroblasts and the human fibrosarcoma cell line HT-1080. Stimulation with fMLP triggers a dose dependent migration of these cells and induces signal transduction including intracellular calcium flux and a transient increase in f-actin. The fMLP-induced adhesion and motility of fibroblasts on fibronectin requires functional PKC and PI3K. This is the first report of a functional formyl peptide receptor in cells of fibroblast origin and opens new possibilities for the role of fibroblasts in innate immune responses.