Within this niche the bacterium employs a variety of mechanisms to evade host immune response. Lipopolysaccharides (LPS) on the surface of H. pylori are modified to WH-4-023 in vivo display certain human blood group antigens, primarily Lewis antigens X and Y [4–7], and less frequently H type 1, i-antigen, blood group A, or Lewis antigens A or B [8–10]. These surface LPS antigens are necessary for the establishment of infection, because mutant strains defective for LPS O-antigen synthesis or for Lewis X/Y expression fail to colonize

mice [11–13]. There is evidence that Lewis antigens expressed on the bacterial surface contribute to adherence of H. pylori to gastric epithelial cells [10, 14], and play a role in tissue tropism [15–17]. Gastric epithelial cells also express Lewis Autophagy Compound Library antigens [18, 19], suggesting that the display of Lewis antigens on the bacterial surface may serve as PCI-34051 a mimicry strategy.

Studies of clinical isolates [18, 20] and experimental infections in animals [21] support this role for bacterial Lewis antigens in immune evasion. In human infection, H. pylori Lewis antigens have been linked to the severity of peptic ulcer and duodenitis [16, 22]. Another important feature of H. pylori LPS is its modified lipid A structure, with reduced acylation and fewer charged groups than is typical of enterobacteria [23]. These lipid A modifications minimize endotoxic and inflammatory properties of H. pylori LPS (reviewed in [24]). Cholesterol is a nonessential nutrient for H pylori, though it promotes growth in serum-free media [25, 26]. H. pylori specifically incorporate cholesterol into the bacterial membrane [27], as do a limited number of pathogenic and commensal bacteria including Proteus mirabilis, Lactobacillus STK38 acidophilus, Borrelia sp., and Mycoplasma [28–30]. Cholesterol may strengthen the membrane in these organisms [30–32]. H. pylori also uniquely form cholesterol α-glycoside [33, 34], and this metabolite can be further modified by acylation or phosphatidylation

[34]. Alpha-glucosylated cholesterol subverts host immune response to the bacterium in a mouse model, through suppression of phagocytosis and of T cell activation [35]. Other roles for cholesterol and cholesterol metabolites in the bacterial membrane have yet to be explored. In this report, we demonstrate that the biosynthesis of lipopolysaccharide, including Lewis antigen expression and LPS core/lipid A modification, are altered by availability of cholesterol in the growth medium. We present data indicating that these changes in the cell envelope may significantly influence the pathogen/host interaction in an animal model of infection. Methods Bacterial strains and growth conditions Strains of H pylori included the laboratory strain ATCC43504 (origin: Australia), 26695 (UK), clinical isolate G27 (Italy [36], provided by N.