Circadian Clock Protein CRY Controls B-Cell Intrinsic Tolerance

The circadian system regulates numerous physiological processes including adaptive immune system. Here we show that mice deficient for the circadian genes Cry1 and Cry2, (Cry double knockout [DKO]) display an autoimmune phenotype including higher serum IgG concentration than wild type (WT) mice, presence of serum anti-nuclear antibodies, precipitation of IgG, IgM and complement 3 (C3) in glomeruli, and massive infiltrations of leukocytes into the lung and kidney. A large panel of autoantigens demonstrated that the sera of the Cry DKO mice but not the WT mice, had autoantibodies covering most of the specificities reported to be present in patients with SLE, rheumatoid arthritis (RA), multiple sclerosis (MS), Sjögren's syndrome and other autoimmune disorders. Taken together, lost of the CRY circadian protein leds to severe autoimmunity. Furthermore, flow cytometry analysis of lymphoid organs showed lower pre-B cell numbers and higher mature recirculating B cells in the bone marrow as well as increased number of B2 B cells in the peritoneal cavity of Cry DKO mice.

The BCR-proximal signaling pathway plays a critical role in peripheral B cell tolerance and activation. Activation of splenic B cells from the Cry DKO mice elicited markedly enhanced and prolonged tyrosine phosphorylation of cellular proteins compared to WT mice, suggesting that a very active BCR signaling pathway may contribute to impaired B cell tolerance in the Cry DKO mice. In summary, our results suggest that B cell development, as well as the intrinsic checkpoints of immune tolerance, are under direct circadian control.