GPI and rheumatoid arthritis: The blocking of OX40 prevents the development of RA in K/BxN mice (T cell receptor [TCR] and the MHC class II molecule A[g7]), which have high titers of anti-glucose-6-phosphate isomerase (GPI)-specific autoantibodies, a reduced percentage of Tfh17 cells and upregulation of autoantibody sialylation.