Localization of MHC Class II/Human Cartilage Glycoprotein-39 Complexes in Synovia of Rheumatoid Arthritis Patients Using Complex-Specific Monoclonal Antibodies

Recently human cartilage gp-39 (HC gp-39) was identified as a candidate autoantigen in rheumatoid arthritis (RA). To further investigate the relevance of this Ag in RA, we have generated a set of five mAbs to a combination epitope of complexes of HC gp-39263–275 and the RA-associated DRαβ1*0401 HLA class II molecules. FACS studies revealed that these mAb recognize specific complexes on homozygous DRαβ1*0401-positive B lymphoblastoid cells pulsed with HC gp-39263–275. The best mAb, 12A, was further characterized using a set of irrelevant DRαβ1*0401-binding peptides and truncated/elongated versions of HC gp-39263–275 itself. The minimal epitope recognized in combination with DRαβ1*0401 was HC gp-39263–273. Peptides not encompassing HC gp-39263–273 were not recognized. Three of five mAb were able to inhibit (up to 90%) the response of HC gp-39263–275-specific DRαβ1*0401-restricted T cell hybridomas to peptide-pulsed APC or purified complexes. Using mAb 12A, we have been able to identify and localize dendritic cells that present DRαβ1*0401/HC gp-39263–275 complexes in synovial tissue of DRαβ1*0401-positive RA patients, indicating local presentation of the HC gp-39263–275 epitope in the inflamed target tissue by professional APC. These data support a role of HC gp-39 in the local autoimmune response that leads to chronic inflammation and joint destruction.