Tissue-associated autoantigens in rheumatoid arthritis. Tissue-antigens detected by autoantibodies in synovial fluid and sera of RA patients

The endogenous danger signal, crystalline uric acid, signals for enhanced antibody immunity

Studies have shown that the immune system can recognize self-antigens under conditions (eg, cell injury) in which the self-tissue might elaborate immune-activating endogenous danger signals. Uric acid (UA) is an endogenous danger signal recently identified to be released from dying cells. Prior work has shown that UA activates immune effectors of both the innate and adaptive immune system, including neutrophils and cytotoxic T-cell immunity. However, it was unclear whether UA could enhance antibody immunity, which was examined in this study. When added to dying tumor cells or with whole protein antigen, UA increased IgG1-based humoral immunity. Further, UA blocked growth of tumor in subsequent tumor challenge experiments, which depended on CD4, but not CD8, T cells. Sera derived from UA-treated animals enhanced tumor growth, suggesting it had little role in the antitumor response. UA did not signal for T-cell expansion or altered tumor-infiltrating leukocyte populations. Consistent with the lack of T-cell expansion, when applied to dendritic cells, UA suppressed T-cell growth factors but up-regulated B cell-activating cytokines. Understanding the nature of endogenous danger signals released from dying cells may aid in a better understanding of mechanisms of immune recognition of self.

Efficient isolation of cDNA clones encoding rheumatoid arthritis autoantigens by lambda phage surface display

Bacteriophage lambda surface display was used to isolate cDNA clones encoding autoantigens recognized by synovial fluid (SF) or sera from patients with rheumatoid arthritis (RA). We constructed cDNA libraries from human synovial sarcoma cells and synovial tissue, using the surface display vector lambdafoo. The cDNA libraries were screened by affinity selection using 40 SF and 44 sera as probes separately immobilized in microtiter wells. Phage clones isolated encode 13 different autoantigens; an unknown protein, two proteins previously unanalyzed as autoimmune antigens, three proteins previously unknown to be recognized by RA sera, and seven known RA antigens. When analyzed their sensitivity and specificity for RA by phage enzyme-linked immunosorbent assay, frequencies of sera that recognize the newly-isolated autoantigens ranged from 20.5 to 6.8% of a panel of RA sera, and 13.6-0% of other autoimmune disease sera. These results indicate that the lambda phage surface display may be powerful for the isolation of cDNA clones encoding autoantigens recognized by SF or sera from patients with not only RA but also other autoimmune diseases.