Dual signaling by innate and adaptive immune receptors is required for TLR7-induced B-cell-mediated autoimmunity - PubMed (original) (raw)
Dual signaling by innate and adaptive immune receptors is required for TLR7-induced B-cell-mediated autoimmunity
Elizabeth R Walsh et al. Proc Natl Acad Sci U S A. 2012.
Abstract
Toll-like receptor 7 (Tlr7) has been linked to systemic lupus disease incidence in humans and mice, but how TLR7 potentiates autoimmunity is unclear. We used a Tlr7 transgenic (tg) mouse model to investigate the cellular and molecular events required to induce spontaneous autoimmunity through increased TLR7 activity. We determined that Tlr7 exerts B-cell-intrinsic effects in promoting spontaneous germinal center (GC) and plasmablast B-cell development, and that these B-cell subsets are dependent on T-cell-derived signals through CD40L and SLAM-associated protein (SAP), but not IL-17. Antigen specificity also factored into TLR7-induced disease, as both a restricted T cell receptor (TCR) specificity and MHC haplotype H2(k/k) protected Tlr7tg mice from spontaneous lymphocyte activation and autoantibody production. Inflammatory myeloid cell expansion and autoimmunity did not develop in Tlr7tgIgH(-/-) mice, suggesting either that spontaneous TLR7 activation does not occur in dendritic cells, or, if it does occur, cannot drive these events in the absence of B-cell aid. These data indicate that autoimmune disease in Tlr7tg mice is contingent upon B cells receiving stimulation both through innate pathways and T-cell-derived signals and suggest a codependent relationship between B cells and T cells in the development of autoimmunity.
Conflict of interest statement
The authors declare no conflict of interest.
Figures
Fig. 1.
Tlr7 promotes the generation of germinal center and plasmablast B cells through B-cell–intrinsic mechanisms. (A and B) 50:50 mix of _Tlr7_tg and WT BM was injected into irradiated WT mice; eight weeks later splenic cell populations were examined by flow cytometry. (A) Number of _Tlr7_tg-derived cells for cell types was expressed as a ratio between _Tlr7_tg and WT cells. (B) The ratio of _Tlr7_tg to WT expression of I-Ab on B cells and CD11c+ cells. Dotted line indicates equal proportions of WT and _Tlr7_tg cells. n = 3 mice/group. (C and D) cDNA derived from follicular B cells of WT or _Tlr7_tg mice was analyzed by (C) microarray (pie chart segments represent percentages of gene categories that contain genes up-regulated more than twofold in at least three mice) or (D) RT-PCR for Ig transcripts of preisotype switched and postisotype switched Ig genes.
Fig. 2.
CD40L and SAP signals are required for the generation of spontaneous autoimmunity in _Tlr7_tg mice. At eight weeks of age, spleens, kidneys, and serum were harvested from _Tlr7_tg, _Tlr7_tg_Cd40lg_−/y, and _Tlr7_tgSAP−/y mice. (A) Representative FACS plots showing GC B-cell percentages (Top) or plasmablasts (Bottom) in _Tlr7_tg (Left), _Tlr7_tg_Cd40lg_−/y (Center), and _Tlr7_tgSAP−/y mice (Right). (B) Representative histograms of surface expression of I-Ab (Left) and SLAM (Right) on B cells from _Tlr7_tg (black line), _Tlr7_tg_Cd40lg_−/y (dotted line), and _Tlr7_tgSAP−/y (gray fill) mice. (C) (Top) Frozen spleen sections stained with B220 (red) and PNA (green) in _Tlr7_tg (Left), _Tlr7_tg_Cd40lg_−/y (Center), and _Tlr7_tgSAP−/y mice (Right). Bars = 50 μM. (Middle) Serum ANA tests. Bars = 50 μM. (Bottom) Histological analysis of representative kidney sections stained with H&E. Bars = 50 μM. (D) Absolute numbers of CD11c+B220+ pDCs and CD11c+CD11b+ mDCs. Experiments are representative of n = 3 mice per group repeated two times. *P < 0.05.
Fig. 3.
Spontaneous autoimmunity in TLR7tg mice requires antigen-specific T-cell help but not IL-17. Irradiated WT mice received BM from _Tlr7_tg_Cd40lg_−/y, or an equal mix of BM from _Tlr7_tg_Cd40lg_−/y and the indicated mouse strain, except for OT-II cells, which were used at a 4:1 ratio. (A) Measured spleen weight. Percentages of (B) FAS+GL7+ B cells; (C) splenic CD21hiCD23low MZ B cells, activated CD69+ B cells, and activated SLAM+ B cells; (D) ICOS+ or CD44+ CD4+ T cells; (E) mean fluorescence intensity (MFI) of I-Ab, SLAM+ B cells or DCs; and (F) ANA+ serum autoantibodies.
Fig. 4.
H-2k/k haplotype or B-cell deficiency in _Tlr7_tg mice confers protection against spontaneous autoimmunity. At 12 weeks of age, livers, kidneys, spleens, and serum were harvested from denoted groups of mice. (A) Total spleen cell counts in WT (white bars), _Tlr7_tgH2b/b (black bars), _Tlr7_tgH2k/b (hatched bars), and _Tlr7_tgH2k/k mice (gray bars). (B) Total numbers of indicated cell types from groups designated in (A): CD11c+ cells (Left), indicated B-cell populations (center panel), and CD4+ T-cell populations (right panel), n = 3 mice/group. (C) Percentage of ANA positive serum, n = 3 mice/group. (D) Total splenocyte cell counts in WT (white bars), _Tlr7_tgIgH+/− (black bars), and _Tlr7_tgIgH−/− mice (hatched bars). (E) Total numbers of CD11b+ cells, CD11b+CD11c+ mDCs, and CD11c+B220+ pDCs (Left), and indicated CD4+ cell populations (Right) from groups described in D, n = 2 mice/group, repeated two times. (F) Representative H&E stained kidney and liver sections. (Scale bar, 50 μm.)
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