3.4 Expression of inflammatory chemokines
Comparing the expression of inflammatory chemokines in the mucosa of the
CRS group and the ABRS group, the neutrophil related chemokines IL-6 and
IL-8 were significantly increased in the ABRS group (P<0.05),
but there was no statistical difference in eosinophil related chemokines
between the two groups (Table 3, Fig. 2). Comparison of chemokine
expression in mucosa and polyps on the affected side of CRS showed that
the neutrophil-associated chemokines IL-6, IL-8 and MCP-1 were
significantly increased in polyps (Table 3, Fig. 3).
In all the samples, the contents of IL-5 and GM-CSF were lower than the
detection limit (10pg/ml). Considering the low content of them in
tissues, no valid data could be displayed.
Discussion
ABRS is a common condition and it is difficult to estimate its exact
incidence. About 0.5-2% of children with ARS develop secondary
bacterial infections that lead to ABRS, but most of them can be cured by
anti-infective treatment 1, 10. Studies have found
that when people are stimulated by rhinovirus, local inflammatory
reaction will be caused, IL-6 and IL-8 in nasal lavage fluid will
increase11. RV-1B infection can promote the
endocytosis of Staphylococcus aureus by lung cells
cultured with semi-permeable membranes, and induce the release of IL-6
and IL-8 and the overexpression of ICAM-112. In our
study, the results of bacterial culture of nasal sinus secretion showed
that the most common bacteria were Staphylococcus (12 cases),
followed by Streptococcus (5 cases), and the rest were multiple
infections.
In order to rule out the presence of primary CFTR dysfunction caused by
potential CF patients in the CRS group, SCLs and WES were performed, and
parental generation verification was performed in patients with
non-SNPs. CF diagnosis was ruled out after analyzing the results. In
other words, children with these mutations do not normally affect the
amount or function of CFTR protein in the body. However, in the case of
exposure to allergens or invasion of microorganisms such as viruses, the
anti-strike ability and recovery ability of CFTR may be weakened13.
Acquired CFTR dysfunction is mostly associated with epithelial mucosal
injury caused by acute and chronic infection, inflammation, hypoxia and
environmental pollution8. Virus invasion causes nasal
mucosal epithelial injury, and stimulates the immune response and repair
mechanism to prevent the virus from causing persistent airway
injury14. However, when the immunity of the body is
not enough to clear the virus or the viral load is too high and the
virulence is too strong, the CFTR function of mucosal epithelium cannot
be restored in time, and the mucus fluidity under the airway mucosa is
reduced, which leads to acute and chronic infection.
The immune response of the nasal mucosal epithelium is not limited to
release of antimicrobial surfactants and mucus to delay the spread of
pathogens in the airway, but it also expresses and secretes various
cytokines and chemokines to drive the immune response against invading
pathogens in the airway14. In an in vitro study,
infection of human primary nasal epithelial cells with H3N7 resulted in
an exponential increase in IFN α, IL 28A, and IL 29. The chemokines and
the inflammatory markers such as CXCL11, RANTES, IL-1, IL-6, IL-8, are
rapidly produced and released 14. In this study, the
expression of CFTR mRNA in the ABRS group was lower than that in the CRS
group, and the IL-6 and IL-8 associated with neutrophils were
significantly increased in the ABRS group. When activated in an
inflammatory response, neutrophils can kill pathogens directly by
phagocytosis or degranulation and indirectly by releasing TNF-α, IL-1,
IL-8, IL-6, IFN-γ 11, 15. These factors stimulate the
production of downstream factors and recruit more neutrophils or other
leukocytes to the site of infection or inflammation, exerting
anti-inflammatory effects 16, 17. In combination with
the results of this study, we speculate that the extremely low CFTR mRNA
caused by acute inflammation of nasal mucosa makes CFTR function
seriously impaired, which not only easily aggravates the proliferation
of pathogens such as bacteria, but also plays a certain role in the
chemotaxis of neutrophil.
The etiology of nasal polyps is complex, which is a chronic inflammatory
lesion of nasal mucosa. Eosinophils, macrophages and dendritic cells can
participate in the activation, release, induction and regulation of a
variety of cytokines to mediate inflammatory processes. Tissue
remodeling caused by chronic inflammation and immune response eventually
leads to nasal polyps 18. In the CRS group, we
compared the expression of CFTR mRNA and inflammatory chemokines in the
ipsilateral mucosa and polyps of the same patient. It was found that the
expression of CFTR mRNA in polyps was significantly lower than in
mucosa. Thi et al. showed the expression of CFTR in nasal polyps was
significantly lower than that in nasal mucosa, which was also supported
by our results19. The formation of nasal polyps,
epithelial barrier damage and rupture is an important feature, and
colonized bacteria and other pathogens, such as Staphylococcus aureus,
etc., aggravate the epithelial barrier damage20.
Moreover, the hypoxic environment of the sinuses in CRS patients may
also cause locally acquired CFTR dysfunction when polyps block the nasal
or sinus drainage pathways, and may initiate a cascade of persistent
fluid and electrolyte abnormalities in the sinuses8.
Some findings suggest that local persistent hypoxia may lead to acquired
CFTR dysfunction in nasal mucosa, resulting in mucociliary dysfunction
in CRS21, 22.
In recent years, more and more data show that the endotype of CRS in
different races is not the same. CRSwNP is mainly eosinophilic
inflammation in western countries. However, CRS is characterized by
non-eosinophilic inflammation in Asia23, 24. In this
study, we also observed that the neutrophil-mediated chemokines IL-6,
IL-8 and MCP-1 were significantly increased in polyps, while the
expression of eosinophil-associated chemokines was not significantly
different between mucosa and polyps. Some studies found that IL-6 was
elevated in CRS polyps and GRO, IL-8 were positively correlated with
IL-6, suggesting that IL-6 may enhance neutrophil recruitment to the
site of infection25. Therefore, we hypothesized that
chronic inflammation of the nasal mucosa and pathogen infection not only
cause CFTR dysfunction, but also cause neutrophil chemotaxis. And
because of local mucosal hyperplasia or swelling, resulting in local
hypoxia microenvironment, which further lead to CFTR dysfunction: The
intracellular H2O could not be discharged out of the cell along with
Cl-, which participated in the formation of nasal
polyps.
This study is a single-center study, so the sample size is limited. Due
to the limitation of sample collection, local mucosa and polyps may not
represent the inflammation status of all mucosa. Besides, baseline data
on CFTR expression in the nasal mucosa of children are lacking due to
the unavailability of nasal mucosa tissue from healthy children.
However, we still observed differences in CFTR expression in different
inflammatory states of nasal mucosa. In this study, the detection
results of eosinophil chemokines IL-5 and CSF were below the lower limit
of detection. Considering their low amount of content in the sample, the
data were unreliable, so they could not be included in the analysis and
discussion. Future studies with larger sample sizes and more sensitive
reagents and assays will be considered to explore the role of neutrophil
chemotactic factor and eosinophil chemotactic factor in rhinosinusitis.
Conclusion
Acquired CFTR dysfunction and neutrophil chemokine play a role in the
development of acute and chronic rhinosinusitis in children. CFTR
dysfunction and neutrophil chemokines IL-6 and IL-8 play more important
roles in ABRS than in chronic inflammation of nasal mucosa and may play
a role in the occurrence and development of nasal polyps.