Intestinal microbial diversity during early-life colonization shapes long-term IgE levels

Abstract

Microbial exposure following birth profoundly impacts mammalian immune system development. Microbiota alterations are associated with increased incidence of allergic and autoimmune disorders with elevated serum IgE as a hallmark. The previously reported abnormally high serum IgE levels in germ-free mice suggests that immunoregulatory signals from microbiota are required to control basal IgE levels. We report that germ-free mice and those with low-diversity microbiota develop elevated serum IgE levels in early life. B cells in neonatal germ-free mice undergo isotype switching to IgE at mucosal sites in a CD4 T-cell- and IL-4-dependent manner. A critical level of microbial diversity following birth is required in order to inhibit IgE induction. Elevated IgE levels in germ-free mice lead to increased mast-cell-surface-bound IgE and exaggerated oral-induced systemic anaphylaxis. Thus, appropriate intestinal microbial stimuli during early life are critical for inducing an immunoregulatory network that protects from induction of IgE at mucosal sites.

Graphical abstract

Figure 1

Absence of Microbial Colonization Leads to Elevated Serum IgE Levels (A) Total serum IgE levels were measured in >4-week-old germ-free (n = 102; gray circles) and SPF (n = 24; black circles) mice. Each point represents an individual mouse, and the horizontal dotted line marks the lower limit of detection of the IgE ELISA assay (0.8 ng/ml). (B) The gating strategy for identifying IgE⁺ basophils is shown for one representative germ-free mouse (top). Linear regression analysis of the frequency of FSC^loSSC^loCD19⁻Thy1.2^dullIgE⁺ blood basophils and total serum IgE levels (n = 40; bottom). r² = 0.2314; p = 0.0017. (C) Total serum IgA, IgM, IgG1, IgG2b, IgG2c, and IgG3 were measured in germ-free (n = 8–10; gray circles) and SPF (n = 8–10; black circles) mice. Each dot represents an individual mouse. ^∗∗∗p ≤ 0.001, ^∗∗p ≤ 0.01, ^∗p ≤ 0.05 by an unpaired Student’s t test.

Figure 2

IgE Levels Become Elevated Early in Life and Are Not Triggered by Food Antigens (A) Total serum IgE levels were determined in SPF mice (n = 4) cohoused with germ-free mice with high IgE levels (n = 4; gray circles) or left with SPF littermates (n = 5; black circles). IgE levels were measured before (day 0) and after cohousing (day 44). (B) Serum IgE was determined longitudinally from 25–64 days of age in germ-free mice fed a conventional autoclaved chow diet (n = 4; gray circles) or an antigen-free elemental diet (n = 4; white circles) or in SPF mice (n = 4; black circles). (A and B) Each point represents an individual mouse, and the horizontal dotted line marks the lower limit of detection of the IgE ELISA assay (0.8 ng/ml). Data for germ-free and SPF animals is representative of at least three independent experiments, and data for antigen-free mice are from one experiment.

Figure 3

Isotype Switch to IgE Is Initiated in Mucosal Lymphoid Tissues Early in Life (A) Normalized expression (to gapdh) of εGLTs from B cells activated in vitro with IL-4 and anti-CD40 (anti-CD40 + IL-4) and ex vivo spleen and MLNs of naive or Heligmosomoides polygyrus (Hp)-infected SPF mice. Each bar represents the mean ± SD of three technical repeats. The MLN and spleen samples were pooled from 3–4 mice. (B) Normalized expression (to gapdh) of εGLTs in spleen, MLNs, and PPs of germ-free mice at the indicated ages. Each bar represents an individual biological sample (one to two pooled mice; n = 1–4 biological samples per time point) ± SD of technical triplicates. nd, not detected. εGLTs was not detected in bone marrow, peripheral lymph nodes, and peritoneal cavity. (C) PP ontogeny was inhibited in utero by intravenous administration of anti-iL-7Rα mAb in 14.5-day pregnant germ-free dams as depicted (top). Total serum IgE levels were measured in the progeny of untreated (n = 5–6; gray circles) and anti-iL-7Rα-treated (n = 7; black circles) dams. Each point represents an individual mouse, and the horizontal dotted line delineates the lower limit of detection of the IgE ELISA assay (0.8 ng/ml). Data are pooled from two independent experiments.

Figure 4

IgE Induction in Germ-free Mice Is Dependent on CD4⁺ T Cells (A) Germ-free mice were left untreated (n = 5; gray circles) or were depleted of CD4⁺ cells by intraperitoneal injection of anti-CD4 mAb (n = 6; black circles) two times per week starting on the day of weaning until the end of the experiment. IgE levels were measured at the start (28-days-old) and the end (96-days-old) of the experiment. Representative data from two independent experiments is shown. (B) Total serum IgE levels were measured in germ-free (n = 16; gray circles) and SPF (n = 8; black circles) TCRβδ^−/− mice. (A and B) Each point represents an individual mouse, and the horizontal dotted line marks the lower limit of detection of the IgE ELISA assay (0.8 ng/ml). ^∗∗p ≤ 0.01; n.s, not significant. p > 0.05 with an unpaired Student’s t test in (A).

Figure 5

IgE Induction in Germ-free Mice Is Dependent on IL-4 (A) Normalized expression (to gapdh) of Il10, Il13, and Il4 from CD4⁺-enriched cells isolated from spleen, MLNs, PPs, and cLPs from the indicated groups of GF and SPF mice. Each bar represents the mean ± SD of 3–4 mice, except for samples from day 22 and cLPs, where the bar represents the mean ± SD of triplicate measurements of samples pooled from 3-4 mice. (B) Germ-free mice were left untreated (n = 4; gray circles) or administered an IL-4-neutralizing monoclonal antibody (n = 5; black circles) or an isotype control (n = 4; hollow circles) by intraperitoneal injection two times per week from the time of weaning until the end of the experiment. IgE levels were measured at the start (28 days old) and/or the end (62 days old) of the experiment. Representative data from two independent experiments are shown. (C) Lymphopenic germ-free Rag1^−/− mice were adoptively transferred with purified wild-type CD4⁺CD3⁺CD25⁻CD45RB^high naive T cells in combination with IgM⁺CD19⁺B220⁺CD3⁻ naive B cells from wild-type C57BL/6 (n = 11), IL-4Rα^−/− (n = 8), or MHC II (I-A^b)^−/− (n = 7) donors, as indicated. Total serum IgE levels were measured 86 days posttransfer. Pooled data from two to three independent experiments per group are shown. (B and C) Each point represents an individual mouse and the horizontal dotted line delineates the lower limit of detection of the IgE ELISA assay (0.8 ng/ml). (D) Representative flow cytometry plots after intracellular staining for IFN-γ and IL-17A of MLNs, PPs, cLPs, and SI CD4⁺ T cells from germ-free and SPF mice after 4 hr of phorbol myristate acetate and ionomycin stimulation in the presence of Brefeldin A. The proportion of cytokine-producing CD4⁺ T cells is indicated in each quadrant ± SD. ^∗∗∗p ≤ 0.001, ^∗∗p ≤ 0.01, ^∗p ≤ 0.5; n.s, not significant. p > 0.05 with an unpaired Student’s t test in (A–C). See also Figure S1 and Table S1.

Figure 6

Increased Intestinal Bacterial Diversity in Neonates Abrogates Hyper-IgE (A) Germ-free C57BL/6 mice were colonized with an SPF flora by cohousing with an SPF sentinel at the indicated age after birth (n = 4–10 mice per group). Total serum IgE levels were measured >100 days after SPF colonization. (B) Total serum IgE levels were measured in adult germ-free C57BL/6 mice that were orally administered three to six gavages of 2 × 10⁹−10¹⁰ CFU of the auxotrophic E.coli strain HA107 before weaning (n = 12), bicolonized from birth with ASF519 (P. distasonis) and ASF361 (L. murinus) (n = 14), ASF colonized from birth (n = 52), or colonized from birth with a low-complexity microbiota (LCM) consisting of approximately 40 species (n = 6). (C) Total serum IgE levels were measured in adult (>6 weeks old) ASF mice raised in a flexible film isolator within individual cages as indicated (n = 2–6 per cage). (D) DNA was isolated from fecal pellets or cecal contents of ASF mice during early (30–40 days old) or adult (77–295 days old) stages, and individual ASF species were detected by species-specific qPCR. Each bar represents the diversity (number of species detected) within an individual mouse, and specific ASF species present are shown by colored squares as indicated. ASF457 (Mucispirillum schaedleri) was not detected in any of the samples. (A–C) Each point represents an individual mouse, and the horizontal dotted line delineates the lower limit of detection of the IgE ELISA assay (0.8 ng/ml). ^∗∗∗p ≤ 0.001; n.s, not significant. (p > 0.05) with an unpaired Student’s t test. See also Figure S2 and Table S2.

Figure 7

Germ-free Mice Display Increased Antigen-Induced Oral Anaphylaxis (A) Representative flow cytometry plots from peritoneal mast cells identified as c-kit⁺IgE⁺ and mean fluorescence intensity (MFI) of mast cell surface IgE and c-kit staining in germ-free, bicolonized, and SPF C57BL/6 mice. Data shown are representative of four independent experiments. (B) Representative histological sections (20× magnification) from ears stained for chloroacetate esterase activity indicative of mast cells (arrows) and summary of mast cell quantification per high-power field (hpf; 20×) of germ-free and SPF mice. Data are indicated by mean ± SEM of 7–10 HPF per mouse and three to four mice per group. (C) Germ-free (circles) and SPF (squares) BALB/c mice were subcutaneously sensitized with Alum alone (open symbols) or OVA + Alum (closed symbols) and, 2 weeks later, challenged with 100 μg OVA intravenously (n = 3 per group; active systemic anaphylaxis, left) or with 50 mg OVA orally (n = 6–9 per group; active oral anaphylaxis, right). Rectal temperature was measured every 5–10 min for 60 min, and the maximal Δtemperature [°C] is plotted. Data for the active oral anaphylaxis is pooled from two independent experiments. (A and C) Each point represents an individual mouse, and the horizontal dotted line indicates the mean. ^∗∗∗p ≤ 0.001, ^∗∗p ≤ 0.01, ^∗p ≤ 0.5; n.s, not significant. p > 0.05 with an unpaired Student’s t test. See also Figure S3.