B lymphocytes confer immune tolerance via cell surface GARP-TGF-β complex
Caroline H. Wallace, Bill X. Wu, Mohammad Salem, Ephraim A. Ansa-Addo, Alessandra Metelli, Shaoli Sun, Gary Gilkeson, Mark J. Shlomchik, Bei Liu, Zihai Li
Caroline H. Wallace, Bill X. Wu, Mohammad Salem, Ephraim A. Ansa-Addo, Alessandra Metelli, Shaoli Sun, Gary Gilkeson, Mark J. Shlomchik, Bei Liu, Zihai Li
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Research Article Immunology

B lymphocytes confer immune tolerance via cell surface GARP-TGF-β complex

Abstract

GARP, a cell surface docking receptor for binding and activating latent TGF-β, is highly expressed by platelets and activated Tregs. While GARP is implicated in immune invasion in cancer, the roles of the GARP-TGF-β axis in systemic autoimmune diseases are unknown. Although B cells do not express GARP at baseline, we found that the GARP-TGF-β complex is induced on activated human and mouse B cells by ligands for multiple TLRs, including TLR4, TLR7, and TLR9. GARP overexpression on B cells inhibited their proliferation, induced IgA class-switching, and dampened T cell–independent antibody production. In contrast, B cell–specific deletion of GARP-encoding gene Lrrc32 in mice led to development of systemic autoimmune diseases spontaneously as well as worsening of pristane-induced lupus-like disease. Canonical TGF-β signaling more readily upregulates GARP in Peyer patch B cells than in splenic B cells. Furthermore, we demonstrated that B cells are required for the induction of oral tolerance of T cell–dependent antigens via GARP. Our studies reveal for the first time to our knowledge that cell surface GARP-TGF-β is an important checkpoint for regulating B cell peripheral tolerance, highlighting a mechanism of autoimmune disease pathogenesis.

Authors

Caroline H. Wallace, Bill X. Wu, Mohammad Salem, Ephraim A. Ansa-Addo, Alessandra Metelli, Shaoli Sun, Gary Gilkeson, Mark J. Shlomchik, Bei Liu, Zihai Li

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Figure 4

B cell–specific Lrrc32-KO mice have increased susceptibility to chemically induced experimental lupus.

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B cell–specific Lrrc32-KO mice have increased susceptibility to chemical...
WT and B cell–specific GARP-KO bone marrow chimeric mice were injected with 500 μl pristane i.p. at 3 months after bone marrow reconstitution. Three months after pristane injection, mice were sacrificed and analyzed for the presence of lupus-like signature (n = 6 WT and n = 6 KO). (A) IgG ANAs in the serum were detected 2 weeks and 3 months after pristane injection. Serum was diluted 1:80 for 2-week analysis and 1:300 for 3-month analysis. (B) Urine protein concentration was measured by Bradford analysis from endpoint (3 months after pristane), with urine diluted 1:50 (n = 4 WT and n = 5 KO), as urine was not obtained from all mice. (C and D) IgG (C) and IgM (D) deposition in the kidneys was quantified. Representative images are shown (n = 4 WT and n = 5–6 KO). Scale bar: 50 μm. (E) Active and total TGF-β1 levels were measured in the sera of the mice using ELISA. (F) GARP and LAP expression on the surface of peripheral B cells in WT and GARP-KO mice was quantified at baseline and 3 months after pristane treatment and analyzed by flow cytometry. (G) The lungs of WT and GARP-KO BM chimera mice were perfused with 4% paraformaldehyde and resected 3 months after pristane injection. Lungs were sectioned and stained with H&E. Black arrows point to immune cell infiltrate clusters, which are quantified by pathology score. Each image is representative of 1 mouse. Scale bar: 200 μm. Statistical analysis was performed by 2-tailed t test; *P < 0.05, **P < 0.01, ***P < 0.001. Error bars represent SD.