Alterations in peripheral blood lymphocyte cytokine expression in obesity

Abstract

Obesity is characterized by alterations in immune and inflammatory function. In order to evaluate the potential role of cytokine expression by peripheral blood mononuclear cells (PBMC) in obesity-associated inflammation, we studied serum protein levels and mRNA levels in PBMC of interleukin (IL)-6, IL-1beta, tumour necrosis factor (TNF)-alpha and IL-1Ra in nine lean and 10 obese subjects. Serum IL-1beta was undetectable, IL-1Ra serum levels were elevated, serum levels of TNF-alpha were decreased and serum levels of IL-6 were similar in obese subjects compared to lean subjects, while transcript levels of IL-6, IL-1beta and TNF-alpha, but not IL-1Ra, were decreased in PBMC from obese subjects. PBMC from obese subjects did, however, up-regulate cytokine expression in response to leptin. Thus, obesity-associated changes in IL-1Ra serum levels and IL-6 mRNA levels were not correlated with changes in cognate mRNA and serum levels, respectively, while TNF-alpha serum levels and PBMC mRNA levels were both decreased in obese patients. While immune alterations in obesity are manifest in peripheral blood lymphocytes, the general lack of correlation between altered serum levels and altered PBMC gene expression suggests that PBMC may not be the source of aberrant serum cytokine levels in obesity.

Fig. 1

Serum inflammatory cytokine levels. Mean serum cytokine levels in lean and obese subjects as determined by enzyme-linked immunosorbent assay (ELISA). Mean serum interleukin (IL)-1Ra levels were 403 and 1812 pg/ml in lean and obese subjects, respectively (P = 0·004, independent t-test). Mean serum IL-6 serum levels were 7·6 and 6·6 pg/ml in lean and obese subjects, respectively (P = 0·875, independent t-test). Mean serum tumour necrosis factor (TNF)-α serum levels were 83 and 0·8 pg/ml in lean and obese subjects, respectively (P = 0·015, independent t-test). IL-1β was undetectable in the serum of both lean and obese subjects. Error bars are standard error of the mean. Note different ordinate scales.

Fig. 2

Cytokine transcript levels in circulating peripheral blood mononuclear cells (PBMC) from obese subjects. Mean log fold difference in transcript levels in PBMC from obese subjects compared to transcript level in PBMC from lean subjects as referent = 1, as determined by quantitative reverse transcription–polymerase chain reaction (qRT–PCR). Log-fold change in transcript level shown numerically under each bar. Differences significant for interleukin (IL)-1β, IL-6, tumour necrosis factor (TNF)-α (P < 0·005 in each case, single-sample t-test), but not IL-1RA (P = 0·57, single-sample t-test). Error bars are standard error of the mean. The ordinate is log-scale.

Fig. 3

Cytokine concentrations in cultured peripheral blood mononuclear cells (PBMC). Median cytokine concentrations as determined by enzyme-linked immunosorbent assay (ELISA) in supernatants from PBMC from obese and lean subjects cultured with and without leptin. Markedly lower cytokine expression in PBMC from obese subjects compared to PBMC from lean subjects cultured in media only were statistically significant for interleukin (IL)-1β, IL-6 and tumour necrosis factor (TNF)-α (P < 0·001 in all cases, Mann–Whitney U-test), but approached significance only for IL-1Ra (P = 0·072, Mann–Whitney U-test). Differences in cytokine expression in PBMC cultured with media + leptin between obese and lean subject groups were not significant for all cytokines (P > 0·3 in all cases). Differences in cytokine expression in PBMC cultured with media only compared to PBMC cultured with media + leptin within each group (obese or lean) were statistically significant for IL-1β, IL-6 and TNF-α in both lean and obese subject groups (P < 0·01 in all cases, Wilcoxon's signed ranks test), and for IL-1Ra in obese subjects (P = 0·005, Wilcoxon's signed ranks test), but only approached significance for IL-1Ra in lean subjects (P = 0·086). Error bars are interquartile ranges. Note different ordinate scales.