Innate mechanisms in upper airway inflammation with focus on epithelium and neutrophils

Abstract

Mucosal inflammation is a key feature in allergic rhinitis (AR) and chronic rhinosinusitis with nasal polyps (CRSwNP). The traditional idea of the epithelium as a simple barrier and neutrophils as a homogenous cell population, already terminally differentiated, has lately been reconsidered. Recent findings have identified advanced immunological properties of both epithelial cells (ECs) and neutrophil subsets. Toll-like receptors (TLRs) and activin receptorlike kinases (ALKs) constitute important receptors of the ECs in recognizing stimuli leading to inflammatory and biological processes through altered gene expression. The new neutrophil classification, in four various subsets, is based on their expression of FcγRIII (CD16) and L-selectin (CD62L). The various subsets appear to have diverse roles during inflammatory conditions. The overall aim of this thesis is to investigate the role of the epithelial and neutrophil cells in upper airway innate immunity.

Papers I-III explored the role of nasal epithelial cells (NECs) in antigen presentation as well as TLRs and ALKs on ECs in AR and CRSwNP. Major histocompatibility complex class II (MHC class II) as well as co-stimulatory molecules were found on NECs from mice and humans and were upregulated on OVA-sensitized mice. NECs from sensitized mice could take up, process and present antigens in a class II dependent manner for the activation of antigenspecific CD4+ T cells. NECs from AR patients were able to activate autologous T cells against the major birch allergen protein, Bet v 1, and induce an IL-13 release. Normally, TLR9 can be found in NECs, but was found to be almost absent in NECs from the mucosa close to the polyps of CRSwNP patients. The TLR9 expression could be reconstituted by stimulation with its ligand, CpG, both in vitro and in vivo. Stimulation also resulted in a downregulation of VEGFR2, a receptor of angiogenesis, and cytokines. Investigation of polyp ECs revealed an upregulation of ALK1-6. Upon ligand stimulation, a downregulation of factors affecting cell proliferation (Ki67) and inflammation (ICAM-1 and IL-8) was seen. This was even more pronounced when microbial infection was mimicked.

In Papers IV and V, neutrophil subsets were described for the first time in the nasal mucosa and a local shift to the activated subset became evident in AR and CRSwNP. In AR, the activated subset CD16high CD62Ldim was shown to have T cell priming capacities and an ability to enhance eosinophil migration. Neutrophils from CRSwNP patients displayed an upregulation of CD11b, most clearly emphasized on the cells of the activated subset. The corresponding adhesion molecule ICAM-1 was upregulated on the epithelium of polyps.

In summary, epithelial and neutrophil cells in the nasal mucosa of patients with AR and CRSwNP exhibit an alerted receptor pattern with a deranged immunological response. Functional data including T cell activation, migration, adhesion and cytokine release clearly indicate a role for TLRs, ALKs and activated neutrophils in these upper airway inflammatory diseases. Further, antigen presenting ECs can contribute to mucosal inflammation in AR.