Fig 2: Dietary fibers and SCFAs dampen CSR, plasma cell differentiation and class-switched antibody responses.After weaning, C57BL/6 mice were fed a fiber diet (regular chow) or no-fiber diet. Two weeks later, these mice were started on SCFAs water (SCFAs) or plain water (Nil). All mice were then administered OVA together with CT via intragastric gavage once a week for 4 weeks starting at 8 weeks of age, and killed a week after the last OVA and CT administration. a Total and OVA-binding IgM, IgG1, IgA, and IgE concentrations in serum of fiber or no-fiber-fed mice on SCFAs water or plain water, as measured by ELISA. Each symbol represents an individual mouse (n = 5 per group, pooled from two experiments). The bars represent the mean ± SD. b OVA-binding IgM, IgG1, IgA, and IgE concentrations in the feces of fiber-fed mice on SCFAs water or plain water, as measured by ELISA. Each symbol represents an individual mouse (n = 5 per group, pooled from two experiments). c IgM, IgA, and IgD-positive cells in the lamina propria, PPs, and MLNs of fiber or no-fiber-fed mice on SCFAs water or plain water as visualized by fluorescence microscopy. d ELISPOT analysis of IgM, IgG1, and IgA AFCs in MLNs, PPs, spleen, and bone marrow of fiber-fed mice on SCFAs water or plain water. e Proportion of surface CD19+IgG1+ and CD19+IgA+ B cells, germinal center B cells (CD19+GL-7+), and plasmablasts/plasma cells (CD138+) in MLNs, PPs, and the spleen of fiber-fed mice given SCFAs water or plain water, as analyzed by flow cytometry. Data in c–e are representative of three independent experiments. *p < 0.05, **p < 0.01, ***p < 0.001, ns: not significant (unpaired t test). Scale bar = 100 µm. The source data are provided in Source Data file.

Fig 3: Dietary fibers and SCFAs alter AID and Blimp1 expression, bacteria-bound/binding antibody responses, and gut bacteria composition.C57BL/6 mice fed a fiber or no-fiber diet were on SCFAs water (SCFAs) or plain water (nil) and administered OVA together with CT (same as in Fig. 1). a, b AID and Blimp1 expression in spleen B cells of these mice, AID expression in spleen B cells of Aicda-/- mice, and Blimp1 expression in naive B cells of C57BL/6 mice, as analyzed by intracellular staining followed by fluorescence microscopy (a) and flow cytometry (b). c Quantification of AID+ and Blimp1+ cells in a and b. n = 3 per group. d Bacteria-bound IgM, IgD, IgG1, and IgA in the feces of fiber diet-fed C57BL/6 mice on SCFAs water or plain water, collected 1 week after the last OVA and CT administration, as well as bacteria-bound IgA in the feces of unimmunized Aicda–/– mice fed fiber diet and plain water, as analyzed by flow cytometry. e Bacteria-bound IgA in feces of fiber and no-fiber diet-fed mice on SCFAs water or plain water as analyzed by flow cytometry. f Concentration of bacteria-binding IgM and IgA in the serum as measured by ELISA; each symbol represents an individual mouse (n = 5 per group, pooled from two experiments). The bars represent the mean ± SD. g Relative abundance of gut bacteria classes (> 1% in any sample group; fiber, no-fiber, and no-fiber + SCFAs) in the mice (n = 4 per group, pooled from two experiments) as determined by high-throughput 16s rRNA gene miSeq sequencing. h Principal component analysis of gut bacterial composition in these three groups of mice on different diets. Data in a, b, d, and e are representative of three independent experiments. *p < 0.05, ***p < 0.001 values, ns: not significant (unpaired t test). Scale bar = 100 µm. The source data are provided in Source Data file.

Fig 4: Dose-dependent and B-cell-intrinsic modulation of Aicda and Prdm1 expression, CSR, SHM and plasma cell differentiation by SCFAs in vivo.a–c C57BL/6 mice on plain water (Nil), SCFAs “lower dose” water (pH = 7.4, 20 mM sodium butyrate, and 30 mM sodium propionate) or SCFAs “higher dose” water (pH = 7.4, 20 mg ml-1 tributyrin emulsion, 140 mM sodium butyrate and 150 mM sodium propionate, SCFAs higher dose. The SCFAs water is referred here as SCFAs “higher dose” as opposed to the “lower dose” used in these experiments for the sake of clarify) were i.p. injected with NP-LPS. a Total and NP3-binding IgM, IgG2b, and IgG3 induced by low dose of SCFAs, as measured by ELISA. Each symbol represents an individual mouse (n = 4–5 per group, pooled from two experiments). Bars represent mean ± SD. b AID and Blimp1 expression in spleen B cells from the same mice, as analyzed by intracellular staining followed flow cytometry. c IgG3+, IgG2b+ B cells, and CD19lowCD138+ plasmablasts/plasma cells in the spleen, as analyzed by flow cytometry. Data in b and c are representative of three independent experiments. d–i NSG/B mice on plain water or SCFAs water (pH = 7.4, 20 mg ml-1 tributyrin emulsion, 140 mM sodium butyrate, and 150 mM sodium propionate) were injected with NP-LPS. d Titers of total and NP3-binding serum IgM, IgG3, IgG2b, and IgA, as analyzed by ELISA. Each symbol represents an individual mouse (n = 5 per group from one experiments). e NP3-binding IgM, IgG3, IgG2b, and IgA AFCs in spleen as analyzed by ELISPOT. f Viable (7-AAD-) spleen CD19+ B cells as analyzed by flow cytometry. g Aicda, Prdm1, germline IH-CH, and post-recombination Iµ-CH transcripts, as analyzed by qRT-PCR and normalized to Gapdh. Data are ratios to B cells cultured with nil (set as 1; means ± SEM of three independent experiments). h Proportion of IgG3+ and IgG2b+ B cells, and CD138+ plasmablasts/plasma cells in the spleen, as analyzed by flow cytometry. i Somatic point mutations in the VH region of VHDJH-C?2b transcripts. Mutations are in pooled sequences from two out of five mice per group. Pie charts depict the proportions of sequences that carry different numbers of point mutations; listed below the pie charts is the overall mutation frequency. Donut charts depict the spectrum of point mutations. Histograms depict frequencies of silent and replacement mutations in FR and CDR regions. *p < 0.05, **p < 0.01, ***p < 0.001, ns: not significant (unpaired t test). The source data are provided in Source Data file.

Fig 5: SCFAs reduce the autoantibody response and autoimmunity in lupus-prone mice.Female MRL/Faslpr/lpr mice fed fiber diet were given SCFAs water (SCFAs) or plain water (Nil) starting at the age of 5 weeks and killed at 17 weeks of age. a Titers of circulating anti-dsDNA IgM, and anti-dsDNA, anti-RNP/Sm, anti-histone, and anti-RNA IgG1 and IgG2a (relative units, RU), as analyzed by specific ELISAs. Each symbol represents an individual mouse (n = 4 per group, pooled from two experiments). The bars represent the mean ± SD. b ANA visualized by indirect immunofluorescence on HEp-2 cells that were incubated with sera (1:400 dilution) from the MRL/Faslp/lpr mice using FITC-labeled rat mAbs to mouse IgG1 and IgG2a. Data are from one of three independent experiments yielding comparable results. c, d AID and Blimp1 expression as analyzed by intracellular staining followed by fluorescence microscopy (c) and flow cytometry (d). e Spleen surface CD138+ plasmablasts/plasma cells, and intracellular CD138+ IgG1+ and CD138+ IgG2a+ plasmablasts/plasma cells as analyzed by flow cytometry. Data are representative of three independent experiments yielding comparable results. f Dorsal skin lesions (left panels), kidney sections stained with H&E (middle panels), and kidney sections stained with FITC-labeled rat mAbs to mouse IgG1 and IgG2a (right panels). Data are representative of three independent experiments. *p < 0.05, **p < 0.01, ***p < 0.001, ns: not significant (unpaired t test). Scale bar = 50 µm (b), 20 µm (c), and 100 µm (f). The source data are provided in Source Data file.