ARS | Publication request: Dietary strawberries increase proliferative response of CD3/CD28-activated CD8+ T cells and production of tumor necrosis factor-alpha in lipopolysaccharide-stimulated monocytes from obese humans

Submitted to: British Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 1, 2013
Publication Date: N/A

Interpretive Summary: Obesity increases the risk of developing bacterial and viral infections compared to normal weight. In a 7 wk human study, twenty obese volunteers were fed a freeze-dried strawberry powder or strawberry-flavored placebo preparation to determine effects of dietary strawberries on immune function. Blood was collected at 6 timepoints during the study, including 2 baseline blood draws and 2 blood draws each during the 3 wk on the strawberry or placebo diets (at the 2 and 3 wk timepoints). Immune cells were isolated from blood at each timepoint and the T cells were activated with antibodies that bound to the cell surface. Monocytes were isolated and activated with a component of bacteria called lipopolysaccharide. The production of immune cell molecules (cytokines) was measured to show the activation status of the T cells and monocytes. The cytokines interferon-gamma, tumor necrosis factor-alpha, interleukin-4, and interleukin-10 were measured for the activated T cells. The cytokines tumor necrosis factor-alpha, interleukin-1beta, interleukin-6, and interleukin-8 were measured for the activated monocytes. Also, the activated T cells were stained with a fluorescent dye to measure the number of cell divisions that occurred after activation. The cell divisions of the two subpopulations of T cells were measured using a fluorescence-activated cell sorter. The two subpopulations that were measured were helper T cells (CD4+) and cytotoxic T cells (CD8+), help clear cancer cells and cells infected with viruses. No difference was observed for the production of T cell cytokines between the groups receiving the different diets. However, the production of tumor necrosis factor-alpha was increased in the activated monocytes from the group consuming strawberries compared to the placebo. Also, a modest increase in the proliferation of the CD8+ T lymphocyte population was observed after activation. These results suggest that dietary strawberries may increase the immunological response of T lymphocytes and monocytes in obese people who are at greater risk for developing infections.

Technical Abstract: Obesity increases the risk of developing bacterial and viral infections compared to normal weight. In a 7 wk double-blind, randomized, crossover trial, twenty obese volunteers (20-50 y old, BMI between 30-40 kg/m2) were fed freeze-dried strawberry powder or strawberry-flavored placebo preparations to determine effects of dietary strawberries on immune function. Blood was collected at 6 timepoints during the study, including 2 baseline blood draws and 2 blood draws each during the 3 wk intervention periods (at the 2 and 3 wk timepoints). Peripheral blood mononuclear cells (PBMCs) were isolated at each timepoint and activated with CD3 plus CD28 antibodies (T lymphocyte activation) or lipopolysaccharide (LPS, monocyte activation). Interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-4, and IL-10 were measured in supernatants from activated T cells. Supernatants from the activated monocytes were measured for the production of TNF-alpha, IL-1beta, IL-6, and IL-8. PBMCs were prestained with PKH dye and activated with CD3 plus CD28 antibodies to determine the proliferative responses of CD4+ and CD8+ T lymphocytes by flow cytometry. No difference was observed for the production of T cell cytokines between the intervention groups. The production of TNF-alpha was increased in the supernatants from LPS-activated PBMCs in the group consuming strawberries compared to the placebo. A modest increase in the proliferation of the CD8+ T lymphocyte population was observed at 24 h post-activation. These data suggest that dietary strawberries may increase the immunological response of T lymphocytes and monocytes in obese people who are at greater risk for developing infections.