Dietary strawberries increase the proliferative response of CD3/CD28-activated CD8⁺ T cells and the production of TNF-α in lipopolysaccharide-stimulated monocytes from obese human subjects

Abstract

Obesity increases the risk of developing bacterial and viral infections compared with normal weight. In a 7-week double-blind, randomised, cross-over trial, twenty obese volunteers (BMI between 30 and 40 kg/m 2 ) were fed freeze-dried strawberry powder or strawberryflavoured placebo preparations to determine the effects of dietary strawberries on immune function. Blood was collected at six time points during the study and peripheral blood mononuclear cells (PBMC) were isolated at each time point and activated with CD3 plus CD28 antibodies (T-lymphocyte activation) or lipopolysaccharide (LPS, monocyte activation). Interferon-g, TNF-a, IL-4 and IL-10 were measured in supernatants from the activated T cells. Supernatants from the activated monocytes were analysed for the production of TNF-a, IL-1b, IL-6 and IL-8. PBMC were pre-stained with PKH (Paul Karl Horan) dye and activated with CD3 plus CD28 antibodies to determine the proliferative responses of CD4 þ and CD8 þ T-lymphocytes by flow cytometry. To detect global changes in gene expression, microarray analysis was performed on LPS-and vehicle-treated PBMC from two subjects before and after the strawberry intervention. No difference was observed for the production of T-cell cytokines between the intervention groups. The production of TNF-a was increased in the supernatants from LPS-activated PBMC in the group consuming strawberries compared with the placebo. A modest increase in the proliferation of the CD8 þ 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.

Clinical evidence on potential health benefits of berries

“…Similar trend was seen after intake of freeze-dried strawberries [40,41], which also increased immunological response in obese subjects [42].…”

Dietary grape powder increases IL-1β and IL-6 production by lipopolysaccharide-activated monocytes and reduces plasma concentrations of large LDL and large LDL-cholesterol particles in obese humans

“…We have recently reported that dietary strawberries induce beneficial changes in blood lipid profiles and sensitise ex vivo -derived monocytes in response to an immunological stimulant ( 21 , 22 ) . In the present study, we expanded our analyses to another fruit to further define the potential benefits of consuming different fruits in the obese population.…”

Increased cytokine production by monocytes from human subjects who consumed grape powder was not mediated by differences in dietary intake patterns

“…In a separate intervention study, we observed an increase in the production of the pro-inflammatory cytokine TNF- in LPSstimulated monocytes from obese subjects after consuming strawberry powder [32]. In the study with strawberry powder, the subjects were given all of their meals for the duration of the study, which substantially reduced the likelihood that changes in dietary patterns influenced the production of TNF- in the monocyte population [32]. In the study with grape powder, we utilized dietary recall data in order to eliminate the possibility that diet was responsible for mediating the increased sensitivity of the monocyte population to LPS.…”

“…Previously, we determined that consumption of grape powder increased the production of two pro-inflammatory cytokines IL-1 and IL-6 by monocytes from obese subjects after ex vivo-stimulation with the bacterial component LPS [22]. In a separate intervention study, we observed an increase in the production of the pro-inflammatory cytokine TNF- in LPSstimulated monocytes from obese subjects after consuming strawberry powder [32]. In the study with strawberry powder, the subjects were given all of their meals for the duration of the study, which substantially reduced the likelihood that changes in dietary patterns influenced the production of TNF- in the monocyte population [32].…”

“…All values are presented in the Tables as unadjusted means ± SD and differences were considered significant at P < 0.05. As previously described [22], the power analysis for the study was performed using results from our prior study in obese human subjects who were fed strawberry powder [31,32]. We used the differences observed for TNF- concentrations from the strawberry study as the endpoint, and calculated using a power of 0.8 and an expectation of a 10% difference in cytokine production between the interventions with grape and placebo groups.…”