Overweight and obese adult humans have a defective cellular immune response to pandemic H1N1 influenza A virus

Abstract

Objective: Obese adults have a greater risk of morbidity and mortality from infection with pandemic H1N1 influenza A virus (pH1N1). The objective of the present study was to elucidate the specific mechanisms by which obesity and overweight impact the cellular immune response to pH1N1.

Design and methods: Peripheral blood mononuclear cells from healthy weight, overweight, and obese individuals were stimulated ex vivo with live pH1N1 and then markers of activation and function were measured using flow cytometry and cytokine secretion was measured using cytometric bead array assays.

Results: CD4(+) and CD8(+) T cells from overweight and obese individuals expressed lower levels of CD69, CD28, CD40 ligand, and interleukin-12 receptor, as well as, produced lower levels of interferon-γ and granzyme B, compared with healthy weight individuals, suggesting deficiencies in activation and function are indicated. Dendritic cells from the three groups expressed similar levels of major histocompatibility complex-II, CD40, CD80, and CD86, as well as, produced similar levels of interleukin-12.

Conclusions: The defects in CD4(+) and CD8(+) T cells may contribute to the increased morbidity and mortality from pH1N1 in obese individuals. These data also provide evidence that both overweight and obesity cause impairments in immune function.

Figure 1. Activation and function of dendritic cells remain intact in PBMCs from overweight and obese individuals

PBMCs were incubated with (filled bar) or without (open bar) live pH1N1 virus and dendritic cell populations were analyzed. There were no differences in (a) total CD3⁻CD11c⁺ dendritic cells, nor in (b) activated dendritic cells expressing CD80 and CD86, (c) MHC-II, and (d) IL12 among any of the BMI groups in both unstimulated and stimulated PBMCs. Data were collected on approximately 30,000 events run in the dendritic cell/monocyte gate. Results are displayed as the mean ± s.e.m. (n=26-28 per group).

Figure 2. Activation and function of CD4⁺ T cells are impaired in PBMCs from overweight and obese individuals

PBMCs were incubated with (filled bar) or without (open bar) live pH1N1 virus and CD4⁺ T cell populations were analyzed. Total CD4⁺ T cells (a) were similar among groups, while CD4⁺ T cells expressing CD69 (b), as well as, activated CD4⁺ T cells expressing CD28 (c), CD40L (d), IL12R (e), IFNγ (f), both IFNγ and GrB (g), and CD28, CD40L, IFNγ, and GrB (h), were significantly lower in stimulated PBMCs from overweight and obese individuals, compared to healthy weight individuals. There were no differences in unstimulated PBMCs among groups. Data were collected on approximately 50,000 CD3⁺ events run in the lymphocyte gate. Results are displayed as the mean ± s.e.m. (n=26-28 per group). *P<0.05 compared to stimulated PBMCs from healthy weight individuals.

Figure 3. Activation and function of CD8⁺ T cells are impaired in PBMCs from overweight and obese individuals

PBMCs were incubated with (filled bar) or without (open bar) live pH1N1 virus and CD8⁺ T cell populations were analyzed. Total CD8⁺ T cells (a) were similar between healthy weight and obese individuals, while numbers were higher in overweight individuals. CD8⁺ T cells expressing CD69 (b) and IFNγ (c), as well as, activated CD8⁺ T cells expressing CD28 (d), CD40L (e), IFNγ (f), both IFNγ and GrB (g), and both CD28 and IL12R (h), were significantly lower in stimulated PBMCs from overweight and obese individuals, compared to healthy weight individuals. There were no differences in unstimulated PBMCs among groups. Data were collected on approximately 50,000 CD3⁺ events run in the lymphocyte gate. Results are displayed as the mean ± s.e.m. (n=26-28 per group). *P<0.05 compared to stimulated PBMCs from healthy weight individuals.

Figure 4. PBMC cytokine secretion from overweight and obese individuals suggests a shift towards a T_H2-dominated response

Secreted cytokines were measured in supernates from PMBCs incubated with (filled bar) or without (open bar) live pH1N1 virus. There were no differences in IL12 (a) and IL7 (b) levels between the healthy weight and overweight groups and the healthy weight and obese groups, both from unstimulated and stimulated PBMCs. IL5 levels (c) were higher and IFNγ levels (d) trended lower in stimulated PBMC supernates from obese individuals, compared to healthy weight individuals, while there were no differences in unstimulted PBMC supernates. Fold increase (filled bar) between unstimulated and stimulated PBMC supernates was lower for TNFα (e) and trended lower for IL6 (f), in stimulated PBMC supernates from obese individuals, compared to healthy weight individuals. Results are displayed as the mean ± s.e.m. (n=14-16 per group). Data below the limit of detection were assigned a value of half the lower limit of detection. The lower limits of detection of the assays were as follows: IL12, 0.6 pg/mL; IL7, 0.5 pg/mL; IL5, 1.1 pg/ml; and IFNγ, 1.8 pg/ml. *P<0.05 compared to PBMCs from healthy weight individuals within treatment group.