Nasal polyps in patients with CRSwNP are characterized by a diversity of Th phenotypes and cytokines, activated B cells and plasma cells, and infiltration of eosinophils and neutrophils [21,22,23], but studies comparing the immune profile and endotyping of nasal polyp tissue in the AERD group compared with the non-AERD group of patients with CRSwNP are very limited.

In the current study, we revealed that among immunoglobulin isotypes, only IgE serum levels were significantly higher in the AERD group than in the non-AERD group. In addition, the overall percentage of eosinophils, neutrophils, and plasma cells in the histopathological evaluation of nasal polyp samples was significantly higher in the AERD group than in the non-AERD group. There were also significant increases in GATA3, IL4, IL5, and IL17 gene expression levels in nasal polyp tissue from the AERD group compared with the non-AERD group.

According to our findings, only IgE serum levels showed a significant increment in the AERD group compared with the non-AERD group.

Although aspirin sensitivity is not an allergen-specific IgE response due to the absence of aspirin-specific IgE antibodies, evidence indicates that atopic sensitization to classical allergens is widespread in patients with AERD and some patients show higher total serum IgE levels [24]. Elevated IgE binds to high affinity- FcεRI located on the surface of mast cells and basophils, leading to the activation of these cells, which can secrete various pro-inflammatory mediators, including IL4, IL13, histamine, and eicosanoids, all of which can contribute to the exacerbation of symptoms [25].

According to studies, eicosanoids are produced in an unbalanced way by people with CRSwNP. Both AERD and non-AERD groups produce more pro-inflammatory leukotrienes (LT) and fewer anti-inflammatory prostaglandins (PGs), but this phenomenon is more severe in patients with AERD. For instance, higher levels of LTE4 in nasal, bronchial, and urine fluids, especially following NSAID exposure, higher levels of PGD2 metabolites in their urine and plasma, and decreased PGE2 synthesis and its receptor EP2 [26]. In addition, although the treatment of patients with CRSwNP is very confusing and different treatments have distinct effects on patients, anti-IgE therapeutic strategies such as omalizumab are effective and quick-acting because they prevent the overproduction of PGs and cysteinyl LTs in addition to functioning as a mast cell stabilizer for patients with AERD [27].

In line with our study, Bangert et al. reported higher serum IgE levels in the AERD group of patients with CRSwNP [28]. Elevated IgE serum levels in patients with CRSwNP are mainly due to excessive tissue overspill [29]. In this regard, Bucheit et al. showed that nasal polyps from the AERD group had a higher frequency of plasma cells in addition to increased levels of local antibodies and a higher rate of antibody class switching compared with polyps from the non-AERD group [30], although in another study they found that class switching not only to IgE but also to IgG4 was higher in the AERD group of patients with CRSwNP with recurrent polyps. They further claimed that enhanced IgG4 synthesis is probably to compensate for the effect of elevated IgE and has a protective effect against the development of nasal polyps in these patients [31].

Based on our results, both AERD and non-AERD groups were eosinophilic forms of CRSwNP, although eosinophil infiltration was significantly higher in the AERD group than the non-AERD group of patients with CRSwNP. Consistent with our study, Stevens et al. showed elevated infiltration of eosinophils in the AERD group compared with the non-AERD group, indicating a higher infiltration rate of eosinophil-mediated inflammation in nasal polyps [32]. Also, Bangert et al., similar to what was mentioned in our study, introduced the AERD group in CRSwNP as a predominantly eosinophilic Th2 inflammation. They noted that the percentage of IL5Rα+ cells, including eosinophils and mast cells, was significantly higher in the AERD than the non-AERD group following a significant increase of Th2 molecules such as IL5 and CCL7 and a trend towards increased IL13 levels in the nasal secretions of the AERD group, although we did not observe a significant difference in the count of mast cells between these two groups [28]. These findings, in accordance with the results of our study, emphasize the predominant Th2 eosinophilic inflammation in the AERD group. Eosinophils stimulate the nasal mucosa, which produces mediators such as TSLP, IL25, and IL33. More eosinophils and mast cells are recruited and activated by these mediators and release more inflammatory molecules, followed by more Th2 inflammatory cells and further inflammation. The existence of this self-perpetuating phenomenon, which is clearly shown in the AERD group due to the higher infiltration of eosinophils, has also been supported by other investigations [28, 33, 34]. Previous studies have shown that more eosinophil infiltration in patients with CRSwNP can be associated with disease severity, poor response to treatment, and recurrence after surgery. Based on our knowledge, although high infiltrating and the key role of neutrophils in nasal polyp formation and mucosal inflammation in patients with CRSwNP have been mentioned in previous studies [35,36,37], there is no information on the comparison of polyp tissue neutrophil counts between the AERD and the non-AERD groups in patients with CRSwNP. In polyp tissue, we found that neutrophil counts, like eosinophils and plasma cells, are significantly higher in the AERD than in the non-AERD groups. In addition, previous studies have shown that increased neutrophilia in nasal polyps reduces the response to therapies and is related to disease recurrence [38, 39].

As previously stated, research comparing nasal polyp endotyping in patients with AERD and non-AERD types of CRSwNP is extremely rare. In the present study, we revealed significantly higher gene expression levels of GATA3, IL4, IL5, and IL17 in the AERD group than the non-AERD group, demonstrating the predominance of Th2 inflammation among these patients. Similar to our results, in a study published in 2020 by Scott et al., the prevalence of Th2 inflammatory cytokines was demonstrated with significantly higher levels of IL5, IL13, and IFNγ in the AERD group than the non-AERD group [40], although in our study, gene expression levels of IFNγ did not differ between the AERD and the non-AERD groups. They also noted that the inflammation pattern can even be completely different among the AERD group in patients with CRSwNP [40]. On the other hand, contrary to our study, Stevens et al. reported that despite the increased gene expression levels of Th2 inflammation mediators, including IL4, IL5, and IL13, when comparing patients with CRSwNP to patients with CRSsNP and controls, there was no difference in the expression of these genes between the AERD and the non-AERD groups of patients with CRSwNP [32].

As with our results, no significant difference was reported in IL1β gene expression levels between the AERD and the non-AERD groups [28]. It is worth mentioning that some research has also found a rise in Th2 mediators in the Nasal Lavage Fluids (NFL) sample, which appears to be indicative of their content in polyp tissue [41].

Even though, based on previous studies, a Th17-dominant inflammatory pattern can typically be found in patients with CRSsNP [42], elevated mRNA expression levels of IL17 and RoRγt in patients with CRSwNP compared with controls have also been claimed [43]. Until present, no comparison of Th17 mediators between the AERD and the non-AERD groups of patients with CRSwNP has been described. Despite the absence of a significant difference in the gene expression level of RoRγt, we discovered a significantly higher gene expression level of IL17 in the AERD group than in the non-AERD group.

It has been shown that endotyping nasal polyps based on gene expression levels in patients with CRSwNP, compared with phenotyping, provides a more comprehensive approach by identifying local lymphocyte subtypes and cytokines, which determine the predominant type of inflammatory microenvironment and can be used in improved diagnostic and therapeutic approaches [44, 45].

In contrast to our research, there are studies that describe the inflammatory pattern of Asian patients with Th17 and Th1 predominance [46, 47]. Also, Wang et al. were demonstrated that there appears to be an extraordinary diversity in immunologic endotypes of CRSwNP in Europe, China, Japan, and Australia [48]. According to these cases, ethnicity can be suggested as one of the contributing factors to the development of CRS and subgroup differentiation. Also, Katotomichelakis et al. stated that the inflammatory patterns of nasal polyps in the same geographical area may change over time [49].

CRS and its treatment, especially in cases of CRSwNP with recurrent polyps, is one of the medical challenges, and performing targeted treatments can be one of the important achievements in the treatment of affected people. Numerous investigations have been carried out for this goal to assess the profile of immune cells and associated cytokines. However, investigations into the division of patients with CRSwNP into AERD and non-AERD subgroups have been uncommon. The aim of this study was to evaluate patients with CRSwNP in two AERD and non-AERD groups. The results showed that, in addition to the patients participating in this study having an inflammatory cell profile, CRSwNP patients with AERD showed increased levels of cytokines and different cell profiles. As a result, the results emphasize that CRSwNP individuals can show different cellular and cytokine profiles, and new treatment regimens can be adapted to these inflammatory changes.

This study had several limitations, including patients’ referrals from one center and a narrow study population. Furthermore, due to the non-sterile status of the nasal region, bacterial culture was not performed. We suggest studies with a higher number of participants and broader cytokine measurements. Furthermore, specific IgE measurements may be helpful in future research. The study of Staphylococcus aureus endotoxin as a superantigen can be used to assess the effects of bacterial infection or colonization. In addition, assigning a control group and organizing a case-control study can be helpful in the precise evaluation of the pathophysiology of patients with AERD and non-AERD subtypes of CRSwNP.