Obesity Expands a Distinct Population of T Cells in Adipose Tissue and Increases Vulnerability to Infection

Abstract

Obesity in humans is associated with poorer health outcomes after infections compared with non-obese individuals. Here, we examined the effects of white adipose tissue and obesity on T cell responses to viral infection in mice. We show that lymphocytic choriomeningitis virus (LCMV) grows to high titer in adipose tissue. Virus-specific T cells enter the adipose tissue to resolve infection but then remain as a memory population distinct from memory T cells in lymphoid tissues. Memory T cells in adipose tissue are abundant in lean mice, and diet-induced obesity further increases memory T cell number in adipose tissue and spleen. Upon re-challenge infection, memory T cells rapidly cause severe pathogenesis, leading to increases in lipase levels, calcification of adipose tissue, pancreatitis, and reduced survival in obese mice but not lean mice. Thus, obesity leads to a unique form of viral pathogenesis involving memory T cell-dependent adipocyte destruction and damage to other tissues.

Keywords: LCMV; T cell memory; Trm; obesity; pancreatitis; tissue-resident memory T cells; white adipose tissue.

Conflict of interest statement

DECLARATION OF INTERESTS

The authors declare no competing interests.

Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1.. LCMV Infection of White Adipose Tissue

B6 mice were given LCMV-Armstrong (2 3 105 PFUs, intraperitoneal [i.p.]), and levels of virus in adipose and spleen and leukocyte abundance in adipose were determined. (A) The line graphs represent virus levels mean (±SEM) in the spleen or perigonadal white adipose tissue (WAT) at the indicated days after infection. The dotted horizontal line indicates the limit of detection. Data are pooled from two experiments with three to six mice per group. (B) Perigonadal fat pads were isolated from LCMV-infected mice at day 5 and assessed for viral infection. Gentle centrifugation was used to separate low density mature adipocytes from denser stromal vascular fraction (SVF) cell populations. The graph shows quantification of infectious virus (n = 3, one experiment), with an example of plaques developing in Vero cells. (C) Perigonadal adipose tissue was harvested at the indicated days of infection and analyzed by microscopy. Top: representative sections stained with H&E; scale bar, 120 mm. Bottom: whole-mount staining reveals the lipid droplet in adipocytes (BODIPYC12; red), cell nuclei (Hoechst; blue), and infiltrating T cells (anti-CD3; green); scale bar, 100 mm. Data are representative of two experiments with two or three mice per group. (D) Total number of leukocytes, CD8+ T cells, and CD4+ T cells recovered from fat pads before infection (n = 8) and at day 8 post-infection (n = 6). Data were analyzed using unpaired Student’s t test with **p

Figure 2.. Virus-Specific T Cells Accumulate in WAT

Virus-specific T cells in adipose tissue and spleen were quantified at multiple times after acute infection by tetramer staining and ICCS. (A) Representative dot plots identify DbGP33+CD8+ T cells (left) and IAbGP67+CD4+ T cells (right) before infection and at days 8 and 70 post infection. The numbers indicate the frequency of the tetramer+ cells among all live cells in the spleen or among leukocytes isolated from the fat pads. (B) The number (mean ± SEM) of tetramer-positive T cells per spleen or fat pads at the indicated times post-infection. Data are drawn from two independent experiments with three to five mice per group. (C) Representative dot plots show GP33-specific CD8+ T cells or GP61-specific CD4+ T cells expression of IFNg after peptide stimulation. The analyses are from the indicated days after infection, with numbers indicating the percentage of IFNg+ cells among all cells. (D) The number (mean ± SEM) of IFNg+ epitopespecific T cells per tissue in spleen and fat pads as measured using ICCS assay at the indicated times post-infection. Data represent two experiments with five to nine mice per group. (E) T cell co-expression of IFNg with TNF or IFNg with IL-2 in the spleen or fat pads at day 8. CD8+ T cells were stimulated with GP33–41 peptide;CD4+ T cells were stimulated with GP61–80 peptide. See also Figure S1.

Figure 3.. A Distinct Subset of Memory T Cells in WAT

(A and B) B6 recipient mice (Ly5a–) were given TCR-transgenic (Tg+) 2 × 104 P14 CD8+ (Ly5a+) T cells or SMARTA CD4+ (Ly5a+) T cells and then infected with LCMV-Armstrong 1–2 days later. At day 38 post-infection, intravascular (i.v.) staining was performed to label circulating donor CD4+ or CD8+ T cells and distinguish them from T cells within the spleen or adipose tissue. (A) An illustration of the method whereby intravenous staining is coupled to ex vivo staining that labels all T cells in suspension. (B) Representative dot plots showing the proportion of T cells protected from intravenous staining because of their location within the parenchyma of the spleen or WAT. Note that the vast majority of T cells purified from WAT are not contaminants from circulating subsets. Data represent three independent experiments with three or four mice per group. (C and D) B6 recipient mice (Ly5a–) were given TCR-transgenic (Tg+) splenic 2 × 104 P14 (Ly5a) or SMARTA (Ly5a+) T cells and then infected with LCMV-Arm 1–2 days after engraftment. At day 38, spleen and WAT cells were isolated and co-stained to identify the donor T cells and their expression of phenotypic markers. (C) The histograms are gated on P14 memory cells (top) or SMARTA memory cells (bottom) and show their surface expression of the indicated molecules. Memory donor cells from spleen (red) or WAT (blue) are shown with naive splenic Tg+ cells (black). Data represent two experiments with four to six mice per group. (D) Memory P14 and SMARTA donor cells from day 50 post-infection were FACS-purified from the spleen or adipose tissue and subjected to RNA sequencing to identify changes in gene expression. The dot plots show donor cells from adipose tissue before and after FACS. The graphs show EdgeR analysis of the RNA-seq data with log fold change (logFC) in RNA expression in WAT T cells relative to splenic T cells plotted against theamount of RNA per cell, expressed as log counts per million reads (logCPM). The red circles identify significant (false discovery rate [FDR]

Figure 4.. Diet-Induced Obesity Increases Memory T Cell Number

Mice were fed lean or high-fat diet for 8–9 weeks to establish obesity prior to LCMV-Armstrong infection. The number of virus-specific T cells in the spleen and fat pads was determined by tetramer staining and ICCS at multiple times after infection. (A) An illustration of the experimental approach. (B) The body weight of the mice and perigonadal fat pads at day 90 post-infection. (C) The line graphs show the number (mean ± SEM) of tetramer-positive T cells per spleen (top) or WAT (bottom) at the indicated times post infection. Data are pooled from two to four independent experiments with a total of three to nine mice per group. (D) The scatterplots show the number of GP33-specific or GP61-specific memory T cells that can make IFNg at day 90, as determined by ICCS assay. Each circle represents an individual mouse. Data represent four experiments with nine mice per group. (E) The line graphs represent the number (mean ± SEM) of DbGP33+CD8+ (left) or IAbGP67+CD4+ (right) T cells per WAT divided by the weight of the fat pad. Data represent two or four experiments with three to nine mice per group. (F) Lymphocytes were isolated from the spleen and fat pads of lean or obese mice at day 90 post infection and exposed to the indicated peptide in an ICCS assay. The graphs show the geometric mean fluorescence intensity (+SEM) among IFNg expression by T cells. Data represent four experiments with nine mice per group. Significance determined by unpaired Student’s t test: *p

Figure 5.. Immune Obese Mice Develop T Cell-Dependent Lethal Acute Pancreatitis upon Re-challenge

Cohorts of mice were fed lean or high-fat diet starting at 4–5 weeks of age until 13–15 weeks of age. Lean mice were 40 g (n = 13). Some of the mice were immunized with LCMV-Armstrong, and the rest were left LCMV naive. Sixty-five days later, the mice were challenged with LCMV-Clone13 (2 × 106 PFUs, i.p.) and analyzed 2 or 5 days later. (A) An illustration of the experimental approach. (B) Survival of naive (solid lines) and immune (dashed lines) mice after challenge, including mice requiring humane euthanasia. Among the re-challenged LCMV-immune mice, a Mantel-Cox log rank test revealed a significant difference (p = 0.0039) between the naive and obese mice. Data represent 7–16 mice/group. (C) Lipase activity in ascites (left) and serum (right) at 2 days post-challenge infection. Dots on figure represent individual mice (3–6 per group, two independent experiments). (D) Representative pancreas sections from the indicated four groups of mice at 2 days post-challenge infection. Sections were stained with H&E (upper two rows) or Von Kossa stain to reveal calcium deposition (dark gray, bottom row). The upper images show regions within the pancreas; the middle bottom images show the margin of the pancreas. Scale bar, 150 μm. (E) Concentrations of IL-6, IFNg, and TNF in blood. Symbols represent individual mice (3 or 4 per group, two independent experiments). Significance determined by unpaired Student’s t test: *p

Figure 6.. Memory T Cells Mediate Acute Pancreatitis and Adipose Tissue Necrosis

Cohorts of lean or obese immune mice were treated with antibodies to CD8 and CD4 to deplete T cells or treated with isotype control antibodies before challenge. Mice were analyzed 2 days after infection. Data compiled from two independent experiments with four to six mice per group. (A) Lipase activity in the peritoneal cavity. (B) Sections of pancreas and adipose stained with Von Kossa. Scale bar, 150 μm. (C) Calcium concentrations in blood. (D) ALT concentration in blood. (E) Body temperature in individual mice. Significance determined by unpaired Student’s t test: *p