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 important component for T cell immune responses. We have generated several monoclonal antibodies (PSRM-1, -2, -3, -6, and -7) against B7-1 using a human glycosylphosphatidylinositol-anchored B7-1 (GPI-B7-1) as an antigen. These monoclonal antibodies are able to detect B7-1 by flow cytometry, 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 antibodies bind to different epitopes. PSRM-3 and -7 detect phosphatidylinositol-specific phospholipase C-released soluble GPI-B7-1 in a sandwich ELISA. 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 ELISA, B7-1 was detected in the synovial fluid of 5/11 patients with rheumatoid arthritis, 5/5 patients with osteoarthritis, and 2/6 patients with other forms, including crystalline-induced arthritis. The presence of soluble B7-1 was confirmed by immunoprecipitation using PSRM-3-coupled Sepharose beads. The source and function of soluble B7-1 are unknown at present; it is possible, however, that the soluble form of B7-1 molecule may play a local immunoregulatory role which may suppress or induce inflammation depending upon whether it interacts with the T cell costimulatory CD28 molecule or the negative signaling CTLA-4 molecule.
McHugh
R S
RS
Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Ratnoff
W D
WD
Gilmartin
R
R
Sell
K W
KW
Selvaraj
P
P
D000069594:Abatacept; D000911:Antibodies, Monoclonal; D000918:Antibody Specificity; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000502:physiology; D001168:Arthritis / Q000276:immunology*; D018122:B7-1 Antigen / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D018106:CD28 Antigens / Q000502:physiology; D060908:CTLA-4 Antigen; D006801:Humans; D018796:Immunoconjugates; D008213:Lymphocyte Activation; D011233:Precipitin Tests; D011994:Recombinant Proteins; D015398:Signal Transduction; D012995:Solubility; D013582:Synovial Fluid / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D000943:Antigens, Differentiation; D018122:B7-1 Antigen; D018106:CD28 Antigens; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; D018796:Immunoconjugates; D011994:Recombinant Proteins; D000069594:Abatacept