The impact of adiposity on adipose tissue-resident lymphocyte activation in humans

R L Travers, A C Motta, J A Betts, A Bouloumié, D Thompson, R L Travers, A C Motta, J A Betts, A Bouloumié, D Thompson

Abstract

Background/objectives: The presence of T lymphocytes in human adipose tissue has only recently been demonstrated and relatively little is known of their potential relevance in the development of obesity-related diseases. We aimed to further characterise these cells and in particular to investigate how they interact with modestly increased levels of adiposity typical of common overweight and obesity.

Subjects/methods: Subcutaneous adipose tissue and fasting blood samples were obtained from healthy males aged 35-55 years with waist circumferences in lean (<94 cm), overweight (94-102 cm) and obese (>102 cm) categories. Adipose tissue-resident CD4+ and CD8+ T lymphocytes together with macrophages were identified by gene expression and flow cytometry. T lymphocytes were further characterised by their expression of activation markers CD25 and CD69. Adipose tissue inflammation was investigated using gene expression analysis and tissue culture.

Results: Participants reflected a range of adiposity from lean to class I obesity. Expression of CD4 (T-helper cells) and CD68 (macrophage), as well as FOXP3 RNA transcripts, was elevated in subcutaneous adipose tissue with increased levels of adiposity (P<0.001, P<0.001 and P=0.018, respectively). Flow cytometry revealed significant correlations between waist circumference and levels of CD25 and CD69 expression per cell on activated adipose tissue-resident CD4+ and CD8+ T lymphocytes (P-values ranging from 0.053 to <0.001). No such relationships were found with blood T lymphocytes. This increased T lymphocyte activation was related to increased expression and secretion of various pro- and anti-inflammatory cytokines from subcutaneous whole adipose tissue explants.

Conclusions: This is the first study to demonstrate that even modest levels of overweight/obesity elicit modifications in adipose tissue immune function. Our results underscore the importance of T lymphocytes during adipose tissue expansion, and the presence of potential compensatory mechanisms that may work to counteract adipose tissue inflammation, possibly through an increased number of T-regulatory cells.

Figures

Figure 1
Figure 1
Lymphocyte phenotype and activation in adipose tissue according to levels of central adiposity. (a) Relative gene expression of cluster differentiation markers to identify T lymphocytes (n=30), (b) CD4+ T lymphocyte subsets present within the adipose tissue (n=30) and (c) proportions of activated T lymphocytes in adipose tissue SVF as a percentage of CD4+ and CD8+ cells measured by flow cytometry (n=17). Gene expression data presented as mean 2−▵▵Ct±s.e.m. Effects of adiposity were analysed by one-way analysis of variance (ANOVA), *P<0.05 and **P<0.001. (d) (i–iv) Correlations between waist circumference and activation status of CD4+ and CD8+ T lymphocytes in the adipose tissue (n=17) were analysed using Pearson's (R) correlation; coefficients shown along with significance values. MFI, mean fluorescence intensity.
Figure 2
Figure 2
Macrophage numbers and activation in adipose tissue with varying levels of adiposity. (a) Relative gene expression of CD68 used to identify macrophages (n=30). (b) Proportions of macrophages in adipose tissue SVF as a percentage of the total cells (n=17). Data are presented as mean 2−▵▵Ct±s.e.m. Effects of adiposity were analysed by one-way analysis of variance (ANOVA), *P<0.05 and **P<0.001. (c) Correlations between waist circumference and proportion of macrophages present in the adipose tissue SVF (n=17) were analysed using Pearson's (R) correlation. MFI, mean fluorescence intensity.
Figure 3
Figure 3
Relative gene expression of parameters related to metabolism, appetite/adiposity and inflammatory cytokines in whole adipose tissue samples with varying levels of adiposity. Data are presented as mean 2−▵▵Ct±s.e.m. with participants classified equally based on waist circumference (n=30). Effects of adiposity were analysed by one-way analysis of variance (ANOVA), *P<0.05 and **P<0.005. Note that IL-10 was expressed in three lean, eight overweight and seven obese individuals. IL-6, IL-8 and IL-1β were detected in all overweight and obese individuals but only in eight, six and nine lean individuals, respectively.
Figure 4
Figure 4
Cytokine secretion by whole adipose tissue explants cultured for 3h with varying levels of adiposity. (a) Adipokine secretion normalised per 100 mg ml−1 adipose tissue cultured. (b) Adipokine secretion multiplied by L1–L4 fat mass to predict total central adipose tissue adipokine secretion. Mean and s.e.m. values were shown for groups based on waist circumference. Effects of adiposity were analysed by one-way analysis of variance (ANOVA), *P<0.05, **P<0.005 and $P=0.06 (lean, n=8; overweight, n=6; obese, n=10).

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Source: PubMed

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