Total phenolic contents in selected fruit and vegetable juices exhibit a positive correlation with interferon-γ, interleukin-5, and interleukin-2 secretions using primary mouse splenocytes

We hypothesized that some fruits and vegetables have an immuno-modulatory potential on T helper type 1 (Th1) and Th2 cytokine secretions. Therefore, Th1 cytokines including interleukin (IL)-2, and interferon (IFN)-γ, and Th2 cytokines including IL-4 and IL-5, produced by mouse splenocytes administrated with 13 selected fruits and vegetables were determined. The results showed that low dose (10 μg/ml) administration with oriental plum, mulberry, peppers (including green, yellow, and red color varieties), ceylon spinach, and red onion significantly (P<0.05) increased IL-2 secretion. Administration with high dose (500 μg/ml) strawberry significantly increased the secretion ratio of IFN-γ/IL-5 (Th1/Th2). Further analysis showed that the stimulatory effects of selected fruits and vegetables on IL-2, IFN-γ, and IL-5 secretions demonstrated a significantly (P<0.05) positive correlation with the total phenolic (including flavonoid) content in the selected fruits and vegetables. The correlation coefficient (r) between total phenolic content (including flavonoid) and cytokine secretions varied in magnitude: IFN-γ>IL-5>IL-2. The coefficients from total phenolic content were much greater than those from the total flavonoid content. The total phenolic and flavonoid contents of oriental plum, mulberry, green pepper, and red onion II showed a significantly positive correlation with the IFN-γ secretion. This study suggests that in vitro supplementation with phenolic-rich fruits and vegetables might demonstrate an immuno-modulatory potential via the regulation of Th1/Th2 cytokine secretions, especially Th1 cytokines. The Th1/Th2 immuno-modulatory potentials of these selected fruits and vegetables will be important and useful for the future exploitation of food materials to develop a novel functional food.