TNF deficiency induces breach of B cell tolerance by altering the homeostasis of the regulatory signals in activated B cells of lupus prone mice

Abstract

Abstract The induction of autoantibodies and autoimmunity in patients treated with TNF inhibitors (TNFi) is well-known, but the mechanism by which TNFi induce breach of B cell tolerance is not known. TNF deficiency induces TFH and TH17 cell expansions and disrupts germinal centers (GC), that regulate high affinity antigen specific antibody production and autoreactive B cell selection. We found that TNF deficiency in Sle1 mice (Sle1.TNF−/−) induced high titers of germline encoded, T-dependent IgG anti-cardiolipin. Upon treated with TLR9 ligand (DNA/curli amyloid protein), Sle1.TNF−/− mice developed high IgG anti-dsDNA; although CD95+PNA+/GL7lowGC phenotype B cells were induced, they did not form GC nor acquire dark zone phenotype, and their Ig heavy chains accumulated low numbers of mutations. Similarly, without proper GC, GC phenotype B cells were found in the TNFR1/2−/−NZM2328 mice, who developed accelerated lupus, suggesting disturbed GC by TNF deficiency dysregulated GC phenotype B cell selection. Using an antibody to Neu5Gc (N-Glycolylneuraminic acid, a CD22 high affinity ligand which is the hydrolyzed product of GL7 ligand, N-acetylneuraminic acid, Neu5Ac), we found that GC phenotype B cells from TNF deficient mice failed to stop hydrolyzing Neu5Ac to Neu5Gc, suggesting a failure in recruitment of CD22 to the BCR complex upon activation. Furthermore, activated B cells from Sle1.TNF−/− mice constitutively expressed high level of pS6 and SHIP-1; whereas, additional stimulants, anti-Ig and/or anti-CD40, were required to induce pS6 expression in those of the Sle1 mice. Here, we report a possible mechanism by which TNF deficiency alters the homeostasis of regulatory molecules such as CD22 and FcgRIIB, and thus activated B cell selection.