Innate immunity genes influence the severity of acute appendicitis

The innate immune response has been highly conserved during evolution. It involves an orchestrated polyphony of local and systemic responses that rapidly destroy invading microbes.1 Key innate immune mechanisms include those that recognize microbial molecular patterns and initiate the local response that attracts and activates leukocytes, increases vascular permeability, elicits pain, and enhances blood flow to the infected tissue.2 Many features of innate immunity are characteristic of acute appendicitis, a common form of moderately severe, yet localized, bacterial infection.3 Although the pathophysiology of acute appendicitis is not entirely understood, obstruction of the appendiceal lumen appears to be the initiating event in most cases.4 Bacterial overgrowth and invasion occur within the distended, obstructed appendix. The bacteriology is complex, involving both aerobic and anaerobic bacterial constituents of the normal gastrointestinal flora.5,6 Pathologically, neutrophil infiltration of the muscularis is a necessary microscopic feature; in complicated disease, it is often accompanied by bacterial invasion. The likelihood of postoperative complications, which are primarily infectious, is strongly related to the severity of inflammation.3,7 In addition, the severity of disease, and thus the risk for developing postoperative complications, has been tied to patient- and surgeon-related delays in surgery and to the lack of health care insurance, factors of considerable importance in the delivery of health services.8,9 Furthermore, appendicitis is also a useful human model of local inflammation, since appendiceal infection elicits both regional and systemic responses and because standard management permits measurement of regional (peritoneal) and systemic (blood) cytokine concentrations. Since the disease is treated, in most cases, by appendectomy and as pathologic examination of the inflamed tissue is always performed, the inflammatory response can be measured and characterized. Additional advantages of acute appendicitis for the study of local inflammation are that many patients are relatively young and healthy prior to developing the disease and the duration of symptoms prior to study is generally short. We hypothesized that the severity of local inflammation, as it occurs in acute appendicitis, can be influenced by polymorphisms in genes involved in innate immunity. To test this hypothesis, we studied patients with acute appendicitis for the occurrence of single nucleotide polymorphisms (SNPs) in genes that encode participants in two general stages of the innate response, microbial recognition and local inflammation. CD14 initiates the response to Gram-negative organisms by binding to bacterial lipopolysacharide (LPS), peptidoglycan, and other bacterial molecules,10 physical contact between CD14-bound LPS, MD-2, and Toll-like receptor 4 (TLR4) initiates LPS signal transduction within macrophages, with the TLR4 molecule being the critical transmembrane component of the signaling pathway for LPS.11,12 Since SNPs in the CD14 and TLR4 genes (CD14 −159 C→T, TLR4 896 A→G) have been associated with altered responses to LPS,13,14 we hypothesized that these SNPs might be present in individuals with complicated appendicitis. In addition to these SNPs in CD14 and TLR4, we also studied polymorphisms in the genes for three proteins that figure prominently in local inflammation, regardless of the inciting factor(s). Tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6) link microbial recognition, as well as many noninfectious stimuli, to acute inflammatory responses. Polymorphisms in the regulatory regions of each of these genes have been associated with altered cytokine responses and outcomes in a variety of experimental and clinical conditions.15–17