Chronic rhinosinusitis and cystic fibrosis: the interaction between sinus bacteria and mucosal immunity

Chronic rhinosinusitis (CRS) is highly prevalent in cystic fibrosis (CF) patients, in whom a close correlation exists between the microbiology of the upper and lower respiratory tracts. We have reported intramucosal bacterial microcolonies in the sinus mucosa from idiopathic CRS patients and have made observations suggesting that these may result from mucosal immunotolerance secondary to altered macrophage function. In this study, we sought to determine whether intramucosal microcolonies exist in the mucosa of CF patients with CRS, and to investigate the associated mucosal immunology.

Mucus swabs and tissue biopsies were taken from 9 patients with CF undergoing functional endoscopic sinus surgery (FESS) for CRS, 11 with idiopathic CRS undergoing FESS, and 9 with normal sinuses having transnasal pituitary surgery. Microbiology samples were taken for culture and intramucosal microcolonies were sought using Gram staining. Mucosal immune cells were identified using fluorescent immunohistochemistry.

Positive culture rates were similar between CRS patients and controls, but there were significantly more intramucosal microcolonies in the CRS groups (8/9 CF-CRS, 7/11 CRS), compared to controls (1/9). Furthermore, the biodensity of intramucosal microcolonies was significantly higher in CF-CRS than idiopathic CRS. Mirroring the microbiological observations, the number of CD163+ macrophages was significantly increased in CF-CRS compared to idiopathic CRS (p = 0.03).

Intramucosal bacteria exist within the sinus mucosa of patients with CF, and in significantly greater numbers than in idiopathic CRS patients. We speculate that intramucosal microcolonies may also exist in the lower respiratory tract mucosa in CF and play a role in disease recalcitrance.