The effects of grapes and their products on immune system: a review

Abstract Immune system plays a significant role in preventing and controlling diseases. Some studies reported the beneficial effects of grapes and their products on immunity. However, their results are controversial. This review aimed to discuss the effects of grapes and their products on immune system and their mechanisms of action. Although various in-vio and in-vitro studies and some human studies suggested that grapes and their products may help to improve the immune system’s function, clinical trials in this area are limited and inconsistent. In conclusions, although, consumption of grapes and their products may help to having a healthy immune syste, further studies particularly human studies are required to clarify the precise effects of them and their mechanisms regarding immune system.


Introduction
The immune system is the first-line defense against infectious agents and foreign invasions.This system is an interactive network of immune cells, humoral agents, and cytokines [1].Immune cells are generated in the bone marrow.Some immune cells including neutrophils, other granulocytes, and B cells differentiate in the bone marrow, while T cells migrate to the thymus to differentiate (e.g., cd T cells, CD8 þ T cells).Moreover, monocytes move through the blood and differentiate into macrophages in the tissues [2].Impaired immune system regulation can lead to severe inflammatory responses and diseases.In addition to the role of the immune system in disinfection and anti-neoplastic protection, recent studies have reported its impact in regulating systemic metabolic homeostasis [3][4][5].Given that the immune system is involved in maintaining health and preventing disease, a better understanding of its regulatory and effective factors has great importance in preventing and improving diseases [6,7].Nutrition and nutrients play a significant role in maintaining the immune system and its responses [8].A diet rich in fruits and vegetables is effective in reducing inflammation and improving immune function due to its antioxidant compounds and other biologically active substances [9].Moreover, some evidence showed that phytochemicals can have modulatory effects on the immune system [2,10].Grapes (Vitis vinifera) and their products are among the possible nutritional effective factors on immune function [11].Grapes and their products (e.g., fruits; grapes juice, fruits and seed extract, powder) contain beneficial compounds such as vitamins (e.g., vitamins E and C), phytochemicals (e.g., anthocyanins, flavan-3-ol monomers, proanthocyanidins, phenolic acids, resveratrol, and flavonols), and other compounds such as melatonin [11][12][13][14][15]. Red and purple grapes have the greatest phytochemicals with antioxidant properties in comparison to white grapes [15].According to the literature, grapes and their products can be effective in preventing and reducing the risk of various diseases such as diabetes, obesity, cardiovascular diseases, and cancer [16][17][18][19].Some in-vitro studies indicated the useful effects of grapes and their products on the immune system [20][21][22].Moreover, the results of several studies on birds showed that the consumption of grapes products improved immunity [23][24][25].Some research in mice also reported that intake of grapes or their products had some useful impacts on the immune system [26][27][28].Human studies particularly clinical trials regarding the effects of grapes and their products on the immune system are limited and controversial [7,[29][30][31][32][33].However, some of them reported some beneficial effects in this area.For instance, the results of a randomized clinical trial (RCT) among healthy individuals showed that consumption of grape juice increased the number of cd T cells and serum levels of vitamin C [7].On the contrary, cd T cells number and serum antioxidant capacity decreased in the placebo group [7].In another RCT study, in patients with allergic contact dermatitis to nickel demonstrated increased levels of interferon-c (INFc), interleukin-4 (IL-4), IL-17, pentraxin 3, IL-10, and decreased nitric oxide (NO) levels in the group received grape polyphenols (GPP) versus the placebo group [29].Moreover, a 9-week cross-over RCT among 24 obese subjects showed that intake of grape powder had immunomodulatory effects versus placebo [32].Available review studies linking the effects of grapes and their products on immunity are limited and have some limitations; they reviewed a small number of studies over restricted grapes products using a finite number of possible mechanisms [19].Given the results of some studies on the beneficial effects of grapes and their products on immunity, a limited number of review studies in this field, and limitations of the conducted review studies, the present review was carried out to fill this research gap.The aim was to discuss the effects of grapes and their products on the immune system and their possible mechanisms of action.

In-vitro and animal studies
Various in-vitro and animal studies reported beneficial impacts of grapes or their products on immunity.For example, in one study on peripheral blood mononuclear cells (PBMC) extracted from a group of obese individuals compared with healthy people, it was found that grape polyphenols increased IL-21 levels in the healthy group, while they reduced the release of IL-1? and IL-6 in the obese people [20].Marzulli et al. 2012 also observed that fermented grape marc increased releasing the anti-inflammatory cytokines and the induction of FoxP3 (a biomarker of T regulatory cells) in human PBMC [21].Another study on human PBMC also concluded that the grape products including red and white wines, as well as grape juice inhibited stimulationinduced effects of mitogens phytohaemagglutinin and concanavalin A such as neopterin production and tryptophan degradation following stimulation of macrophages by releasing IFN-c [22].
Among animal studies, one study indicated that daily grapes intake (2.5 g/kg body weight) in mice reduced oxidative stress and changes in immune function due to chronic ethanol consumption [27].So that, intake of grapes increased IL-4 concentration and reduced tumor necrosis factor alpha (TNFa), INF-c, transforming growth factor beta1 (TGF-b1), vascular endothelial growth factor A (VEGF-A) levels.These beneficial effects were attributed to polyphenols in grapes [27].In another research on broilers, it was found that grape seed extract (GSE) supplementation increased glutathione levels versus the control group (p < 0.01) [25].GSE intake also increased levels of specific antibodies against Newcastle disease virus in the intervention group (p < 0.01) [25].Similarly, one research in broilers reported that the levels of glutathione peroxidase, humoral and cellular immune responses improved in the group with consuming GPP than the control group [24].Although GPP supplementation had no significant effect on total antibody and IgG levels, IgM antibody levels were higher in the GPP group than in the control group [24].Ao et al. 2020 also observed the advantageous effects of GSE supplementation on antioxidant activity and immune system function in ducks [34].One study in mice examined the hepatoprotective effects of triterpenoids and total flavonoids of grapes against liver immunological damage by injection of lipopolysaccharide and bacillus Calmette [26].Based on the findings of this study, medium and high doses of these compounds (150 or 300 mg/kg body weight) decreased IFN-c and IL-2 levels but increased IL-4 and IL-10 levels.However, these substances had low effects on the ratio of Th1 (CD4 þ /CD8 þ , Th1 (IFNc, IL-2)/Th2 (IL-4, IL-10) in the groups with intake of low doses of these compounds (50 mg/kg body weight) [26].The hepatoprotective effects of these compounds were attributed to their antioxidant properties and immune regulatory effects [26].Moreover, several studies in mice demonstrated anti-tumor activities of grapes or their products by immunomodulatory effects such as increasing the activity of lymphocytes and lysosomal enzymes, as well as the phagocytic ability of macrophages [35,36].Hao et al. 2015 reported that consuming 100 or 150 mg/kg of grape-seed proanthocyanidin (GSP) in the weaned piglets was related to increased serum levels of IgG, IgM, CD4, IL-2, total antioxidant capacity, glutathione peroxidase, and superoxide dismutase activity versus the control group [37].However, serum levels of malondialdehyde decreased in the GSP groups versus the control group [37].In the same regard, the results of an animal collagen-induced rheumatoid arthritis model indicated that GSP decreased Th1 cytokines as well as the inflammatory mediators including monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory protein-2 (MIP-2), and intercellular adhesion molecule 1 (ICAM-1).In addition, GSP significantly increased up-regulated the number of proanthocyanin CD4 þ CD25 þ Foxp3 þ regulatory T (Treg) cells and induced Th17/Treg cells to rebalance [38].

Clinical trials
Few clinical trials were carried out on the effects of grapes and their products on the immune system and their findings are controversial [7,[29][30][31][32][33].For example, a single-blind cross-over RCT with four experimental treatments including 500 ml/day of red wine (RW) (12% ETOH v/v), dealcoholized red wine (DRW), and red grape juice (RGJ) among healthy males reported that intake of RW, DRW and RGJ for 2 weeks did not affect immune function [31].Similarly, another cross-over study with the similar experimental treatments as above observed no significant effect on the immune system among healthy non-smoking men with moderate alcohol intake pattern [30].Rowe et al. 2011 evaluated the effect of grape juice consumption on immunity among 85 healthy individuals in a double-blind RCT [7].The participants were randomly assigned into two groups for receiving grape juice or the placebo (360 ml/day) for 9 weeks [7].As a result, the group with consumption of the grape juice had more cd cells and higher levels of vitamin C compared with the placebo group.Moreover, a decrease in serum antioxidant activity, a decrease in cd T cell proliferation, and an increase in DNA strand breakage were observed in the placebo group [7].In the RCT by Magrone et al. 2021; 25 patients with nickel-allergic contact dermatitis were randomly divided into two groups for intake of 300 mg of grape seed-derived polyphenol supplement or a placebo for three months [29].According to the results, the levels of interferon-c, IL-4, IL-17, pentraxin 3, and NO decreased in the grape polyphenol group, while an increase was observed in IL-10 levels in this group.However, no change was found in the placebo group [29].In the same regard, the findings of one RCT in 28 runners demonstrated an increased total antioxidant capacity level without significant impact on the immune system following consumption of purple grape juice (10 mL/kg/min for 28 days) versus an isocaloric, isoglycemic and isovolumetric control beverage [33].Zunino et al. 2013 in a 9-week double-blind, cross-over study among 24 obese subjects observed no difference in producing T-cell cytokines including interferon-c, TNF-a, IL-4, IL-10, and IL-8 in the cells activated with lipopolysaccharide (LPS) or anti-CD3/CD28 antibodies between their intervention groups [grape powder equivalent to 92 g grape powder (the equivalent of approximately 4 servings of fresh grapes) versus placebo/day].Nevertheless, producing IL-1b and IL-6 was increased in LPS-activated cells in the grape powder group versus the placebo group [32].
Some differences between various studies could be because of differences in sample size, characteristics of participants, trial duration, type of grapes products and their dosage, type of phytochemicals and amount of them in grapes products.The number of clinical trials in this field is limited.Furthermore, the sample size and duration of clinical trials are not enough large.Therefore, available evidence based on clinical trials is not very sufficient for conclusive and precise judgment yet.
Some beneficial effects of grapes and their products on immunity have been attributed to their phytochemicals such as anthocyanins, flavan-3-ol monomers, proanthocyanidins, phenolic acids, resveratrol, flavonols, and melatonin [19,[39][40][41].Some mechanisms related to the immunological effects of phytochemicals were presented as follows: increasing the activity of lymphocytes and lysosomal enzymes, the phagocytic ability of macrophages, the levels of immune function markers (such the number of cd T cells), and the antioxidant status.Moreover, these beneficial components had regulatory impacts on intestinal mucosal immunity and anti-allergic effects [19,[39][40][41].Another possible mechanism might be their anti-inflammatory effects via modulating transcription of inflammatory agents.Furthermore, they exhibited modifier effects on cell morphology, ligand-receptor interactions, signaling pathways, and foam-cell formation [19,40,41].

Conclusion
According to available evidence, the results of human studies especially clinical trials regarding the effect of grapes and their products on the immune system are limited and controversial.However, intake of grapes and their products may help to protect and promote immune system function due to having beneficial compounds such as different phytochemicals.Furthermore, more studies especially clinical trials are needed to clarify their exact effects of them and their mechanisms regarding the immune system.