Eric Meffre, PhD

Autoantibody production is a characteristic of most autoimmune diseases including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and type 1 diabetes (T1D). These autoantibodies appear in the serum many years before the onset of clinical disease suggesting an early break in B cell tolerance. We previously established in healthy donors that random V(D)J recombination produce large numbers of autoreactive antibodies. Most developing B cells that express polyreactive antibodies or B cell receptors (BCRs) are silenced in the bone marrow, and additional autoreactive B cells are removed in the periphery. We recently analyzed B cell tolerance in RA patients by testing the specificity of recombinant antibodies cloned from single B cells. RA patients exhibit defective central and peripheral B cell tolerance checkpoints that result in the accumulation of self-reactive mature naïve B cells, likely contributing to the pathogenesis of this disease. Yet the mechanisms that lead to the generation and survival of these autoreactive mature naïve B cells in RA patients are unknown.

Defects in BCR signaling have been reported in B cells from SLE patients who also suffer from defective central and peripheral B cell tolerance checkpoints, suggesting that BCR signaling may play an important role in counterselecting self-reactive B cells. By studying X-linked agammaglobulinemia (XLA) patients who carry mutations in the BTK gene that encodes an essential BCR signaling component, we demonstrated that Btk and therefore BCR signaling is essential in regulating thresholds for human central B cell tolerance. In addition, developing anti-nuclear B cells from IRAK-4- and MyD88-deficient patients failed to be counterselected and demonstrated an essential role for Toll-like receptors in the establishment of human B cell tolerance. Moreover, we recently reported that CD40ligand (CD40L)-and MHC class II-deficient patients who accumulated autoreactive B cells in their mature B cell compartment displayed decreased numbers of regulatory (Treg) and NK T cells in their blood suggesting that these cells may be involved in the establishment of peripheral B cell tolerance in humans.

The long range goal of our research is to further elucidate the mechanisms, molecules and cells that regulate B cell tolerance in healthy humans and that are altered in patients with autoimmune diseases. The working hypothesis is that B cells from RA, SLE and potentially T1D patients suffer from intrinsic signaling defects that result in a central failure to remove autoreactive B cells. In addition, alterations in T cell/dendritic cell functions may affect the counterselection of autoreactive B cells in the periphery. We are currently studying B cell tolerance in patients with CD19, TACI, ICOS, Fas, AID, uracil-DNA glycosylase (UNG) gene defects to identify new pathways and molecules required for the establishment of B cell tolerance. The role of NKT and Treg cells on peripheral B cell tolerance is currently being assessed by analyzing B cell tolerance checkpoints in two primary immunodeficiencies, XLP and IPEX. XLP patients suffer from defective SAP (SLAM associated protein) gene and display normal Treg cells but no NKT cells whereas IPEX patients suffer from Foxp3-deficiency in which no functional Treg cells develop resulting in severe autoimmune manifestations.

Finally, we aim to characterize gene expression profiles using Affimetrix gene chips in unstimulated and BCR-stimulated RA and T1D B cells and compare them to those from healthy donor B cells to potentially identify defective pathways through genes that would fail to be properly regulated.