Fig 1: Immunoglobulin A (IgA) deficiency, specifically in intestinal B cells, increases insulin resistance in high fat diet (HFD)-fed mice. a Weight gain (n = 21 WT, 16 IgA-/- HFD; 4 distinct cohorts) and b organ weights (n = 5 WT, 5 IgA-/-) of IgA-/- mice fed HFD compared to wild-type (WT) littermate controls over 14 weeks of diet. c Fasting glucose (left), fasting insulin (right) (n = 4 WT, 4 IgA-/-), d glucose tolerance test (GTT) (left) also represented by area under the curve (AUC) (right), and e insulin tolerance test (ITT) (left) also represented by AUC (right) in IgA-/- mice fed HFD (n = 12 WT, 12–13 IgA-/-, 3 distinct cohorts). f Weight gain (left) (n = 5 WT, 8 IgA-/- NCD), fasting glucose (middle left), glucose tolerance also represented by AUC (middle right), and insulin tolerance and AUC (right) of IgA-/- mice fed normal control diet (NCD) compared to WT littermate controls after 14 weeks of diet (n = 5 WT, 7 IgA-/- NCD). g Weights (left), fasting glucose levels (left middle), blood concentrations of glucose during GTT and AUC (right middle), and ITT and AUC (right) of 12-week HFD-fed B cell-deficient muMT- (Bnull) mice 2 weeks post adoptive transfer of IgA-/- or WT intestinal pan B cells, or a sham phosphate-buffered saline (PBS) control (n = 2 PBS control, 5 WT gut B cells, 6 IgA-/- gut B cells). Data are means ± SEM. * denotes p < 0.05 and ** denotes p < 0.01
Fig 2: Metformin treatment and bariatric surgery interventions can manipulate intestinal immunoglobulin A (IgA). Frequency and absolute numbers of IgA-producing a B cells (B220+) and b plasma cells (B220−) in the colon of high fat diet-fed mice treated with or without metformin in drinking water (300 mg kg−1 per day) for 14 weeks (n = 5/group). Frequency and absolute numbers of IgA-producing c B cells (B220+) and d plasma cells (B220−) in the colon draining mesenteric lymph node (MLN) (n = 5/group). e Colonic secretory IgA (SIgA) levels in HFD-fed mice treated with or without metformin in drinking water for 14 weeks (p = 0.1). f Weight (left), body mass index (BMI) (middle), and homeostatic model assessment-insulin resistance (HOMA-IR) score (right) of obese patients at baseline and 1 month post-bariatric surgery (n = 14 patients; Wilcoxon’s matched-pairs test). g Left: Representative pie chart demonstrating number of patients with increased vs. decreased fecal IgA 1 month post-bariatric surgery (p = 0.02 χ2chi-square test) and Right: total fecal IgA levels at baseline and one month post surgery (n = 14 patients, p = 0.0676 Wilcoxon’s matched-pairs test). Data are means ± SEM. * denotes p < 0.05, ** denotes p < 0.01, and *** denotes p < 0.001
Fig 3: Immunoglobulin A (IgA) deficiency exacerbates immune-cell-mediated visceral adipose tissue (VAT) inflammation. a Enumeration of crown-like structures (CLS) per ×100 low power field (LPF) (left) and fat cell diameter (right) within the VAT of high fat diet (HFD)-fed WT and IgA-/- after 14 weeks of diet (n = 3 mice/group, 10–12 LPF per mouse for CLS, 120–129 cells from three mice for cell diameter). b Representative histological images of VAT of HFD-fed WT (left) and IgA-/- (right) after 14 weeks of diet (scale bar =100 µm). c Percentage (left) and absolute number (right) of total CD11b+ F4/80+ macrophages within the VAT stromal vascular fraction measured by flow cytometry (n = 5–6 pooled mice, three experiments). d Frequency (left) and absolute number (right) of Foxp3+ CD4+ regulatory T cells (Tregs) in the stromal vascular cells of VAT in IgA-/- mice fed HFD for 14 weeks compared to WT controls (n = 4 WT, 6 IgA-/- pooled mice; 4 experiments). e Relative mRNA expression levels of CCL2 and interleukin-10 (IL-10) within VAT of HFD fed WT and IgA-/- mice (n = 5 WT, 6 IgA-/-, 2 experiments). Data are means ± SEM. * denotes p < 0.05, ** denotes p < 0.01, and *** denotes p < 0.001
Fig 4: The number of immunoglobulin A (IgA)-producing cells is reduced within the intestinal immune system of high fat diet (HFD)-fed mice. Frequency and absolute number of IgA-producing B cells (IgA+ B220+) and plasma cells (IgA+ B220-) within the a, b distal small intestine LP (SB) (n = 7/group, 2 experiments), Peyer’s patches (PP) (n = 17–19/group, 5 experiments), c, d colon LP (n = 6/group, 2 experiments), and e, f colon draining mesenteric lymph nodes (MLNs) (n = 4–5/group) in HFD-fed C57BL/6J mice after 14 weeks compared to normal control diet (NCD)-fed controls. g Representative staining of IgA+ cells within the distal SB (left) and colon (right) in HFD- and NCD-fed mice after 14 weeks of diet (scale bar = 100 µm). h Enumeration of IgA+ cells per ×400 high power field (HPF) in the distal SB (left) and colon (right) in NCD and HFD-fed mice (n = 4/group, at least 10 HPF counted per mouse). i Concentration of secretory IgA (SIgA) within ileal contents (left) (n = 11/group) and colonic stool (middle) (n = 6/group), and IgA antibody titers in the serum (right) (n = 15/group) of NCD and HFD wild-type (WT) mice. Data are means ± SEM. * denotes p < 0.05, ** denotes p < 0.01, and *** denotes p < 0.001
Fig 5: Loss of immunoglobulin A (IgA) promotes pro-inflammatory intestinal T cell responses in high fat diet (HFD)-fed mice. Frequency (left) and absolute number (right) of a CD3+ T cells, b T cell subsets, c interferon-γ (IFNγ) and interleukin-17 (IL-17)-producing (T-helper type 1 (Th1) and Th17, respectively) CD4+ T cells, d IFNγ-producing CD8+ T cells in the distal small intestinal lamina propria (LP) of HFD-fed IgA−/− compared to wild-type (WT) controls (n = 9 WT, 11 IgA−/−, 4 experiments). e Frequency (left) and absolute number (right) of CD3+ T cells, f T cell subsets, g IFNγ- and IL-17-producing (Th1 and Th17, respectively) CD4+ T cells, h IFNγ-producing CD8+ T cells in colon LP of HFD-fed IgA−/− compared to WT controls (n = 7–8 WT, 11–13 IgA−/−, 4 experiments). Data are means ± SEM. * denotes p < 0.05, ** denotes p < 0.01, and *** denotes p < 0.001
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