Rheumatoid arthritis (RA) is a chronic inflammatory disease marked by symmetric polyarthritis and joint destruction. While a specific cause is not known, antibodies are thought to play a role in this disease. RA has also been associated with heterophile """"""""Hanganutziu-Deicher"""""""" (HD) antibodies, which were first detected by agglutination of bovine red blood cells, and later shown to be directed against the non-human sialic acid N- glycolylneuraminic acid (Neu5Gc), which is expressed on such cells. We believe that antibodies are of pathological significance, because human tissues can metabolically incorporate Neu5Gc from dietary sources, mainly red meats and milk products. However, the Neu5Gc monosaccharide cannot by itself fill the binding site of an antibody, and can also be modified and presented in various linkages, on diverse glycans. Indeed we show that the human anti-Neu5Gc antibody response is polyclonal, represented by a spectrum of highly variable anti-Neu5Gc antibody responses in normal human sera. Meanwhile, there is prior evidence that antibodies to Neu5Gc-containing molecules form immune complexes in some RA patients, and that such complexes can contribute to the development of inflammatory synovitis. This application shows the presence of Neu5Gc in synovial tissue and fluid and preliminary data on anti-Neu5Gc antibodies in RA sera using a new glycan microarray that we have developed. We thus propose that some patients with RA suffer disease exacerbations due to Neu5Gc accumulation in joints, originating from dietary sources (red meats and milk products), when combined with certain anti-Neu5Gc antibodies that specifically target Neu5Gc-containing epitopes that are enriched in the joint. Defining such an antigen-antibody combination could identify patients who might benefit from avoiding Neu5Gc in the diet and/or measures to decrease Neu5Gc accumulation. Subpopulations of antibody profiles and/or the Neu5Gc content of synovial fluid might also be effective biomarkers of RA severity, progression, prognosis and/or the monitoring of responses to conventional therapy. It is even possible that this unusual immune process has a causative role in some cases of RA. We will use our glycan microarray for the identification of serum anti-Neu5Gc antibody biomarkers in RA. In this pilot phase, a limited set of validated serum samples from RA patients and controls will be studied, in collaboration with Professor Gary Firestein at UCSD, a renowned expert in RA. Results may also point to possible future studies of some of these antibodies, to determine RA risk in the population. The systems being developed can be upgraded to allow high throughput screening for any potential diagnostic and/or prognostic anti-Neu5Gc- glycan antibodies. We will also study RA synovial fluid and tissue samples to determine if they have accumulated Neu5Gc, and if this has diagnostic or prognostic value.
This research effort will impact public health by developing diagnostic products for Rheumatoid Arthritis to identify patients who may benefit from dietary change. Specifically, these diagnostics will identify patients who have disease exacerbations due to Neu5Gc accumulation in joints from dietary sources (red meats and milk products), combined with certain anti-Neu5Gc antibodies that target specific Neu5Gc-containing epitopes that are enriched in the joint. Defining such a combination may identify patients who could benefit from avoidance of dietary Neu5Gc and/or measures to decrease Neu5Gc accumulation.
