Chemokines play a critical role in the migration of particular types of immune cells towards inflammation and infection sites, affecting the nature of immune responses and the outcomes of acute inflammation (i.e., either termination or progression to chronic inflammation) and the infection (i.e., either deletion, persistence, or the occurrence of immunopathologic reactions) (
46).
As a ligand for CXCR3, CXCL10 mainly triggers the migration of Th1 cells to the gastric mucosa and therefore plays a major role during HP infection (
47,
48). During inflammatory immune responses, CXCL10 chemokine is secreted from keratinocytes, neutrophils, monocytes, eosinophils, as well as endothelial and epithelial cells in response to IFN-γ, recruiting Th1 cells (
49) and triggering cell-mediated immunity against the bacteria and then HP elimination via activating macrophages. Increased CXCL10 expression was observed in
HP-infected human gastric mucosa (
50,
51), and elevated CXCR3 expression was also detected in murine and human stomach mucosa infected with
HP (
50-
52). The abnormal expression of CXCL10 and its receptor, CXCR3, may contribute to the development of
HP-linked PU and gastric cancer (
46). The overproduction of CXCL10 recruits a large number of Th1 cells to the gastric mucosa, causing immunopathologic tissue damages such as PU and gastritis (
48,
53). Our results indicated that in the HAS group, CXCL10 production by HPCE-stimulated PBMCs was significantly higher than by non-stimulated PBMCs, suggesting that adequate CXCL10 production might limit
HP infection rendering the asymptomatic phenotype. However, CXCL10 production was not significantly different between non-stimulated and HPCE-stimulated PBMCs in the PU group. The reasons for these observations remain to be revealed in future investigations. It seems that insufficient CXCL10 production in some stages of
HP infection may lead to the induction of a poor Th1 immune response against the bacteria, which in turn leads to
HP persistence and
HP-induced tissue damage. Our results also indicated that CXCL10 production in GE-treated cells (especially at the dose of 30 µg/mL) was significantly lower compared with HPCE-stimulated PBMCs in the NHS, HAS, and PU groups, suggesting the modulatory effects of ginger on CXCL10 production. Ginger may also directly inhibit CXCL10 secretion from epithelial cells, keratinocytes, endothelial cells, neutrophils, eosinophils, and monocytes (
49) or indirectly suppress the inflammatory mediators of IL-12, IL-18, TNF-α, and IFN-γ, which act as CXCL10 inducers (
54).
According to the results of the present study, CXCR3 expression in HPCE-induced PBMCs was higher than in non-stimulated PBMCs in the NHS, HAS, and PU groups, reflecting the promotion of Th1 immune responses by
HP. The expression of CXCR3 in HPCE-stimulated PBMCs was higher in PU patients than in HAS individuals, suggesting that the uncontrolled activation of Th1 cells may play a role in PU development. The results of the present study indicated that in the NHS, HAS, and PU groups, CXCR3 expression decreased in the HPCE-stimulated PBMCs treated with GE (especially at the 20 and 30 µg/mL doses) compared with untreated HPCE-stimulated PBMCs. These results show that ginger has the capacity to downregulate local Th1 cell responses through reducing the expression of CXCR3, which finally mitigates immunopathological responses. In accordance with these observations, the modulatory effects of GE on the expression of CCR4 and CCR6 chemokine receptors, as well as CXCL10, CCL20, and CCL22 chemokines were indicated in an animal model of EAE (
14,
20).
As a ligand for CCR6, CCL20 mainly triggers the migration of Th17 cells toward inflammatory loci (
46). Mouse macrophages and human gastric epithelial cells produce CCL20 in vitro in response to
HP stimulation (
55,
56). Further,
HP infection attracts CCR6
+ CD4
+ T cells towards human stomach mucosa via CCL20, inducing apoptosis in gastric epithelial cells (
46). As mentioned, CCL20 recruits Th17 cells, which in turn attract neutrophils through inducing the release of neutrophil-attracting chemokines such as CXCL8 from epithelial cells and APCs (
57); however, the recruited neutrophils generally fail to kill
HP bacteria but lead to tissue damage. Our results indicated that in the NHS, HAS, and PU groups, the level of CCL20 production was greater in HPCE-induced PBMCs vs. non-stimulated PBMCs, as well as in HPCE-induced PBMCs from PU patients vs. their counterparts from HAS and NHS individuals. These results indicated that PBMCs from PU patients produced greater quantities of CCL20 than the cells obtained from the HAS and NHS groups. Therefore, CCL20 may play an essential role in PU development. In GE-treated cultures (especially at the doses of 20 and 30 µg/mL), CCL20 production was lower compared with untreated HPCE-stimulated PBMCs from NHS, HAS, and PU individuals. Therefore, the beneficial anti-inflammatory effects of ginger may be partly induced through modulating CCL20 production. Our data also indicated that CCR6 expression was higher in HPCE-stimulated PBMCs than in non-stimulated PBMCs in the NHS, HAS, and PU groups. Moreover, CCR6 expression in HPCE-stimulated PBMCs was higher in the PU than in the NHS group. The elevated expression of CCR6 may result in the aggregation of a large number of Th17 cells in the gastric mucosa, which in turn recruits numerous neutrophils that eventually lead to tissue damage. In addition, CCR6 expression decreased in the HPCE-stimulated PBMCs treated with GE compared with untreated HPCE cells. Therefore, it seems that ginger can downregulate local Th17 cell responses and neutrophil recruitment via reducing CCR6 expression and therefore alleviate immune-mediated tissue injury.
The ligands of CCR4 (CCL17 and CCL22) mainly trigger the migration of Th2 and Treg cells toward infectious agents. The elevated expressions of CCL17 and CCL22 have been detected in antrum biopsy specimens from
HP-infected persons compared with non-infected subjects (
15,
58). In H. felis-induced MALT lymphoma in mice, Treg cells were effectively recruited to the tumour microenvironment via B lymphocyte-derived CCL17 and CCL22 (
59). Likewise, CCL17 and CCL22 recruit Treg and Th2 lymphocytes into stomach mucosa, limiting inflammatory and immune responses against the bacteria and leading to
HP persistence mainly via secreting anti-inflammatory cytokines such as IL-4, IL-10, IL-35, and TGF-β (
46). So, adequate levels of CCL17 and CCL22 may prevent harmful inflammatory responses and tissue damage; however, their overproduction recruits a large number of Th2 and Treg cells to the gastric mucosa, leading to the development of
HP-associated malignancies, including gastric cancer and MALT lymphoma (
46). In PU patients, we observed that CCL17 and CCL22 production was higher in HPCE-stimulated than in non-stimulated PBMCs. Therefore, it seems that in PU patients, a greater CCL17 and CCL22 production is a compensatory mechanism to limit tissue injury. Our results also indicated that CCL17 and CCL22 production was higher in GE-treated (especially at the dose of 30 µg/mL) compared with untreated HPCE-stimulated PBMCs derived from NHS, HAS, and PU individuals, indicating the modulatory effects of ginger on inflammatory responses through upregulating CCL17 and CCL22.
We also observed that CCR4 expression was higher in HPCE-stimulated PBMCs compared with non-stimulated PBMCs in the NHS, HAS, and PU groups. Also, CCR4 expression in HPCE-induced PBMCs from PU patients was lower than in their counterparts from HAS and NHS subjects. These results indicated that the PBMCs derived from PU patients expressed lower levels of CCR4 compared with the PBMCs obtained from the HAS and NHS groups. Therefore, a low expression of CCR4 may reduce the influx of Treg and Th2 cells into stomach mucosa. This phenomenon results in the hyper-activation of pathogenic Th1 and Th17 cells that play key roles in PU development. The results presented here also indicated that in the NHS, HAS, and PU groups, CCR4 expression increased in the HPCE-stimulated PBMCs treated with GE (especially at the dose of 20 µg/mL) compared with untreated HPCE-induced PBMCs. This finding suggested that ginger might upregulate local Treg and Th2 responses via increasing CCR4 expression, finally mitigating immunopathologic reactions such as PU and gastritis.
The composition of the bacterial microbiota varies in different parts of the gastrointestinal tract. In this regard, the least and most populated areas are the stomach and distal colon, respectively (
60). Gastric bacterial microbiota changes during
Helicobacter-associated diseases (
31). In healthy persons, the bacterial microbiome mainly includes
Veillonella spp.,
Clostridium spp.,
Lactobacillus spp.,
Streptococci,
Propionibacterium,
Staphylococci,
Firumicutes,
Bacteroidetes,
Fusobacteria,
Actinobacteria, and
Proteobacteria. In chronically
H. pylori-infected patients, the number of
Actinobacteria,
Bacteroidetes, and
Firmicutes decreased while the frequency of
Spirochetes,
Acidobacteriae, and
Proteobacteriae increased (
31,
61). There are large populations of microorganisms in the gastrointestinal tract, which interact with each other. According to previous studies, some of the bacterial species dwelling in the gastrointestinal tract are sensitive to ginger, and this microbial sensitivity may affect the pattern of
HP sensitivity to treatments.
It should be also noted that
CagA+HP strains induce more potent inflammatory responses and are associated with more serious
HP-linked complications compared with CagA
-HP strains (
62,
63). Thus, here we investigated the effects of GE on the expression of some chemokines and chemokine receptors induced by
CagA+HP. Nevertheless,
CagA-HP strains may similarly induce the expression of inflammatory chemokines and chemokine receptors, but at a lower extent. It seems that GE can modulate the expression of the chemokines and chemokine receptors induced by
CagA-HP strains. Our study encourages conducting more investigations to clarify the effects of ginger on
CagA+HP- and
CagA-HP-mediated inflammatory responses.
In conclusion, the results of the present study revealed that the HPCE-stimulated PBMCs derived from PU patients expressed greater amounts of CCL17, CCL20, CCL20, CXCL10, and CCR6 compared with non-stimulated PBMCs. So, ghinger seems to have the capacity to modulate the expression of pro-inflammatory chemokines and their receptors in the PBMCs obtained from PU patients. It is suggested to perform more studies to divulge the therapeutic potentials of ginger for treating HP-related disorders.