DETECTION OF A SOLUBLE FORM OF B7-1 (CD80) IN SYNOVIAL-FLUID FROM PATIENTS WITH ARTHRITIS USING MONOCLONAL-ANTIBODIES AGAINST DISTINCT EPITOPES OF HUMAN B7-1

The costimulatory molecule B7-1 (CD80) has been shown to be an importa nt component for T cell immune responses. We have generated several mo noclonal antibodies (PSRM-1, -2, -3, -6, and -7) against B7-1 using a human glycosylphosphatidylinositol-anchored B7-1 (GPI-B7-1) as an anti gen. These monoclonal antibodies are able to detect B7-1 by flow cytom etry, ELISA, and Western blotting. One antibody in particular, PSRM-3, blocks the CD28/CTLA-4 interaction with B7-1 and consequently blocks costimulation of T cells. The other PSRM monoclonal antibodies did not compete with PSRM-3 for recognition of B7-1 and also failed to block B7-1 interaction with CTLA-4 and CD28, indicating that these antibodie s bind to different epitopes. PSRM-8 and -7 detect phosphatidylinosito l-specific phospholipase C-released soluble GPI-B7-1 in a sandwich ELI SA, We used this sandwich ELISA to assay for the presence of a soluble form of B7-1 in synovial fluids of arthritis patients. By sandwich EL ISA, B7-1 was detected in the synovial fluid of 5/11 patients with rhe umatoid arthritis, 5/5 patients with osteoarthritis, and 2/6 patients with other forms, including crystalline-induced arthritis. The presenc e of soluble B7-1 was confirmed by immunoprecipitation using PSRM-3-co upled Sepharose beads. The source and function of soluble B7-1 are unk nown at present; it is possible, however, that the soluble form of B7- 1 molecule may play a local immunoregulatory role which may suppress o r induce inflammation depending upon whether it interacts with the T c ell costimulatory CD28 molecule or the negative signaling CTLA-4 molec ule. (C) 1998 Academic Press.