ORIGINAL RESEARCH–SINONASAL DISORDERS Murine complement deficiency ameliorates acute cigarette smoke-induced nasal damage Kara S. Davis, Sarah E. Casey, Jennifer K. Mulligan, PhD, Ryan M. Mulligan, MS, Rodney J. Schlosser, MD, and Carl Atkinson, PhD, Charleston, SC Sponsorships or competing interests that may be relevant to con- tent are disclosed at the end of this article. ABSTRACT OBJECTIVE: Exposure to cigarette smoke is a risk factor for chronic rhinosinusitis. Current literature confirms complement fragments are activated in human nasal mucosa. The mechanism(s) responsible for this activation is unclear. We investigated the effects of cigarette smoke on nasal mucosa in vitro and via a model of cigarette smoke exposure by using animals deficient in comple- ment components. STUDY DESIGN: Prospective, controlled animal and in vitro human cell line study. SETTING: University laboratory. SUBJECTS AND METHODS: Human respiratory epithelial cells were exposed to five, 10, and 20 percent cigarette smoke extract (CSE) in vitro in the presence or absence of human serum. Complement activation was assessed by enzyme-linked immu- nosorbent assay and immunofluorescent techniques. Complement- deficient (C3 –/– ,n = 6; factor B –/– ,n = 50) and sufficient mice (wild type, n = 10) were exposed to the smoke of four cigarettes per exposure for two exposures per day for three days. Mice were sacrificed 12 hours after the last exposure, and the nasal cavity was surgically removed. Histological characteristics were analyzed by the use of a subjective scale and quantitative image analysis scoring systems. RESULTS: In vitro analysis of respiratory cell cultures demon- strated that exposure of serum to CSE resulted in complement activation. Furthermore, immunofluorescent staining for C3d could only be demonstrated in CSE-exposed cultures. In vivo analysis demonstrated that complement deficiency, either C3 or factor B deficiency, resulted in a significant reduction in histolog- ical evidence of damage as compared with wild-type control mice (wild type vs C3 –/– , P = 0.02; wild type vs factor B –/– , P = 0.07; no significant difference between C3 –/– vs factor B –/– ). CONCLUSION: These data demonstrate that cigarette smoke activates the complement system. Furthermore, complement defi- ciency protected against smoke-induced mucosal damage in this small series. © 2010 American Academy of Otolaryngology–Head and Neck Surgery Foundation. All rights reserved. E ach year, chronic rhinosinusitis (CRS) is estimated to affect 14 percent of the adult U.S. population. 1 Not surprisingly, CRS is repeatedly found to have an adverse impact on the daily activities, productivity, and cognitive function of patients. Despite these widespread negative consequences, the treatment of CRS apart from surgical intervention remains largely symptomatic and often does not induce remission of underlying mucosal inflammation. Expertly defined as “in- flammatory conditions involving the paranasal sinuses, as well as the lining of the nasal passages that persist beyond 12 weeks,” a more complete understanding of the inflam- mation characterizing CRS and its mechanism(s) is re- garded as the gateway to developing more definitive treat- ment options. 2 Furthermore, as new types of therapeutic options are developed for other diseases, understanding the pathogenesis of CRS is crucial to predict the therapeutic outcomes of CRS patients to these novel treatments and to research them appropriately. 3 Until recently, much of the study of CRS pathogenesis focused on the adaptive immune system in isolation, includ- ing the relative balance of T helper cell 1 versus T helper cell 2 (Th 2 ) cytokine milieu in response to ubiquitous en- vironmental stimuli, such as bacteria and fungi. These lines of evidence, however, do not explain why only some sub- jects develop CRS and other related conditions to pathogens to which nearly all humans are exposed. Environmental stimuli presented to a person’s nasal mucosa are not unique pathogens; it seems plausible that variations in individual immunologic responses to otherwise-ubiquitous stimuli may contribute to the development of CRS. An emerging theory is the role of the innate immune system and, more important, how it interacts with and modifies responses of the adaptive immune system to induce deregulated immune responses leading to chronic inflammation. Innate immunity is the basic defense of the sinonasal cavity, including anatomical and physiological features of the epithelium, which functions to limit the penetration of environmental stimuli and pathogens, thereby lessening the Received October 17, 2009; revised February 4, 2010; accepted February 16, 2010. Otolaryngology–Head and Neck Surgery (2010) 143, 152-158 0194-5998/$36.00 © 2010 American Academy of Otolaryngology–Head and Neck Surgery Foundation. All rights reserved. doi:10.1016/j.otohns.2010.02.022