The present study describes S100A7 in the nose and how it is regulated during SAR. Nasal administration of LPS induces S100A7 release in healthy non-allergic subjects. Lower levels of S100A7 are seen in NAL fluid from SAR patients than from healthy controls and the levels are further decreased upon allergen provocation. SAR patients having completed ASIT display higher levels of S100A7 in NAL than before initiation of treatment. S100A7 is found to emanate mainly from the nasal epithelium and to activate PBMC and neutrophils to produce cytokines, proliferate and up-regulate adhesion molecule expression. Further, the epithelium-induced S100A7 generation is repressed by the allergic mediators IL-4 and histamine.
We have previously identified S100A7 in the NAL proteome using 2-dimensional gel electrophoresis in combination with mass spectrometry, and demonstrated lower levels in patients with symptomatic SAR compared to controls . The present study, investigating S100A7 in NAL using ELISA, confirms and complements previous data by showing diminished levels in SAR patients outside pollen season compared to non-allergic controls, along with a further reduction in the SAR group after allergen provocation. Moreover, the levels appear to return to normal after immunotherapy treatment. No differences in S100A7 levels among healthy and allergic subjects are seen in serum, which supports the notion of a local role for S100A7 in SAR. Results from immunohistochemical staining and real-time RT-PCR of nasal biopsies clearly demonstrate presence of S100A7 in the epithelium and seromucous glands, and culture of epithelial cells reveals a basal secretion of S100A7. These findings are in accordance with a study by Glaser et al. showing an expression in sebaceous glands in the nose , and recent results by Tieu and colleagues demonstrating reduced levels of epithelial S100A7 in patients with CRS and SAR [14, 15]. It should also be mentioned that in contrast to the low levels of S100A7 seen during inflammatory conditions in the upper airways, there are studies demonstrating an enhanced expression and secretion of S100A7 in the skin of patients with AD [25–27]. Moreover, we have previously detected S100A7 in tonsillar epithelium and lymphocytes (CD19+, CD4+ and CD8+ cells) and found reduced levels in tonsils in response to infection and atopic predisposition . In contrast, blood-derived B and T cells express very low or no levels of S100A7. These discrepancies in expression might be related to compartmental differences. Also, the high antigen load in the tonsils might cause a microbe-induced regulation of S100A7 expression.
Accumulating evidence suggests that there might be intrinsic or disease-driven deficiencies in the epithelial barrier function of the nasal mucosa in AR patients . Indeed, allergics suffer from an ongoing so called minimal persistent inflammation, characterized by e.g. infiltration of inflammatory cells (eosinophils and neutrophils) and up-regulation of epithelial adhesion molecules, which in turn primes the nasal mucosa leading to increased sensitivity and responsiveness to allergen provocation [29, 30]. Likewise, we have recently shown that SAR patients have higher clinical symptom scores, pulmonary nitric oxide production, NAL leukocyte numbers and cytokine levels compared to healthy subjects . The epithelium provides not only a physical barrier through mucociliary clearance and tight junctions, but it can also resist entry of pathogens through the production of antimicrobial defense proteins. The present study shows reduced levels of S100A7 in SAR patients and in response to allergen challenge. In addition to the epithelial disruption seen in the atopic airway , we propose defects in AMPs of this kind to be a factor behind the increased susceptibility to microbial infection often seen during periods of SAR [32–34]. However, patients having completed ASIT have a less pronounced minimal persistent inflammation, manifested by a reduced eosinophilic infiltration into the nasal mucosa and reduced epithelial damage , which in turn can explain the higher levels of S100A7 in NAL fluid among these patients.
Nasal challenge with LPS, as a mimic of bacterial upper airway infection, induces release of S100A7 in NAL fluid from healthy subjects. In line with this, the expression of S100A7 by the human hair follicle epithelium has been found to be inducible upon treatment with prototypical microbial products such as LPS . Interestingly, unpublished data from our lab show that nasal administration of LPS (total dose of 50 μg) in SAR patients does not induce release of S100A7 in NAL (before: 92.2 ± 6.5 vs. 24 h after: 92.0 ± 7.4, p = 0.98). The inability of these patients to respond in terms of S100A7 secretion might be a consequence of their impaired antimicrobial defense system. However, it cannot be excluded that the differential responsiveness to LPS among healthy and allergic subjects is related to the dose, as a 2-fold lower concentration was given to the latter group.
The diminished levels of S100A7 during SAR do not correlate with the infiltration of neutrophils. Instead, IL-4 and histamine are found to suppress the S100A7 secretion by epithelial cells, suggesting that a Th2-like cytokine milieu negatively regulates the S100A7 production. Elevated levels of Th2-biased cytokines have been demonstrated in nasal washings of SAR patients both during pollen season and after allergen provocation [37–39], and Glaser et al. have demonstrated that the TNF-α-induced S100A7 secretion by human keratinocytes is inhibited by IL-4 and IL-13 .
Even though there is a ~2-fold reduction in the concentration of S100A7 in NAL fluid from SAR patients, it should be mentioned that the changes in levels in some of the treatment groups are fairly small, which raises questions regarding the biological significance. However, in real-life, efficient clearance of microbes involves a crosstalk between several different cells, signals and mediators that are triggered simultaneously. This is reflected by e.g. the ability of S100A7 to activate the cellular immunity and the ability of cytokines, including TNF-α, IL-4, IL-6 and oncostatin-M [3, 25], to both positively and negatively regulate the generation of S100A7. Hence, it is not the effect of each single AMP, but the combined actions of different mediators that are of biological importance.
The receptor for secreted S100A7 is still unknown, and consequently its functional relevance is poorly understood. In the present study, we demonstrate that S100A7 activates human PBMC and neutrophils to produce cytokines, proliferate and up-regulate adhesion molecule expression. Neutrophils have previously been reported to secrete cytokines, reactive oxygen species and AMPs in response to S100A7 stimulation , but so far there are no other studies demonstrating an effect on mononuclear cells except for its chemotactic properties for CD4+ T cells .