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Legionella Pneumophila and Helicobacter Pylori: Roles in Pathogenesis and Immunity

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Legionella Pneumophila and Helicobacter Pylori: Roles in Pathogenesis and Immunity Infectious Diseases in Obstetrics and Gynecology 7:58-63 (1999) (C) 1999 Wiley-Liss, Inc. Surface-Associated Heat Shock Proteins of Legionella pneumophila and Helicobacter pylori: Roles in Pathogenesis and Immunity P.S. Hoffman 1. and R.A. Garduno ZDepartment of Microbiology and Immunology, Dalhousie University, Halifax, Nova Scotia, Canada eDivision of Infectious Diseases, Department of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada ABSTRACT Bacterial heat shock proteins (Hsps) are abundantly produced during the course of most microbial infections and are often targeted by the mammalian immune response. While Hsps have been well characterized for their roles in protein folding and secretion activities, little attention has been given to their participation in pathogenesis. In the case of Legionella pneumophila, an aquatic intracellular parasite of protozoa and cause of Legionnaires' disease, Hsp60 is uniquely located in the periplasm and on the bacterial surface. Surface-associated Hsp60 promotes attachment and invasion in a HeLa cell model and may alter an early step associated with the fusion of phagosomes with lysosomes. Avirulent strains of L. pneumophila containing defined mutations in several dot/icm genes are defective in localizing Hsp60 onto their surface and are reduced approximately 1000-fold in their invasiveness towards HeLa cells. For the ulcer-causing bacterium Helicobacter pylori, surface- associated Hsp60 and Hsp70 mediate attachment to gastric epithelial cells. The increased expres- sion of these Hsps following acid shock correlates with both increased association with and inflam- mation of the gastric mucosa. A role for Hsps in colonization, mucosal infection and in promoting inflammation is discussed. Infect. Dis. Obstet. Gynecol. 7:58-63, 1999. (C) 1999 Wilcy-Liss, Inc. KEY WORDS Legiondla pneumophila; Helicobacterpylori; heat shock proteins; cellular immunity; adhesion eat shock proteins (Hsps, also known as stress nodominant proteins are thought of as those that or chaperone proteins), particularly the mem- are either secreted or expressed on the surface of bers of the Hsp60 and HspT0 families, have been microbes, so studies indicating that the Hsp60 of recognized for years as immunodominant antigens Escherichia coli (GroEL) is exclusively located in of many microbial pathogens. 1-3 Moreover, im- the cytoplasm seemed contradictory. In addition, mune responses against bacterial Hsps have often none of the heat shock or stress regulated genes been implicated in certain autoimmune diseases z,3 studied to date encode proteins with signal se- and chronic infections. 4,s Yet, autoimmune disease quences or any other known secretion-specific mo- can be prevented in several animal model systems tif to suggest these proteins are secreted. There- by vaccination with Hsps, 6,7 indicating that the im- fore, early reports implicating Hsps in pathogenesis mune response to Hsps is both complex and can be were not taken too seriously or were thought to be modulated by extrinsic factors. Generally, immu- too preliminary to support a strong case. To begin Grant sponsor: Medical Research Council of Canada; Astra Pharma, Canada; Natural Sciences Engineering Council of Canada. *Correspondence to: Dr. Paul S. Hoffman, Department of Microbiology & Immunology, Sir Charles Tupper Building, Rm 7P, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7. E-mail: [email protected] BACTERIAL HSPS IN PATHOGENESIS HOFFMAN AND GARDUNO Fig. I. Immunolocalization of Hsp60 in L. pneumophila (a) and E. coli expressing recombinant L. pneumophila Hsp60 from pSHI6 (b). Bar indicates 0.1 mm for both panels. to understand what roles Hsps might play inpatho- sections of L. pneumophila, using antibodies specific genesis and host immune response, we have been for Hsp60 and gold-conjugated anti-immuno- investigating Legiondla pneumophi/a, an aquatic mi- globulin (MAb or PAb), the gold particles were crobe that has not evolved with humans, and Hdi- found to surround the periphery of the bacteria cobacterpylori, an organism highly evolved and spe- (see Fig. la), indicating both a periplasmic and a cialized to the human gastric mucosa. While both surface location. 8,9 As a control for these experi- pathogens express Hsps on their surface, the ments, recombinant L. pneumophila Hsp60 was pro- pathogenesis role for these Hsps differs. Our stud- duced from a clone in E. coli. As can be seen in ies suggest that the diversity of function attributed Figure lb, the E. coli bacteria accumulated Hsp60 to Hsps, and in particular to pathogenesis mecha- in the cytoplasm, with little or no gold spheres lo- nisms, is largely determined by cellular location. cated in other compartments or on the surface. Comparative immunogold studies with antibodies LOCALIZATION OF HSPS raised to well-known surface associated antigens (LPS, OmpS) gave results similar to those observed Immunolocalization techniques have been success- with Hsp60 antiserum, 8 supporting the case that fully used to determine the cellular location of Hsp60 is a legitimate surface antigen in L. pneumo- Hsps. Surface localization can be determined with phila. Several studies employing immunogold la- whole bacterial cells by either immunofluorescence beling of whole H. pylori cells showed that Hsp60 (light microscopy) or by immunogold electron mi- was located on the bacterial surface. 1-1z Further, croscopy using monoclonal (MAb) or polyclonal immunogold labeling of biopsy samples from pa- (PAb) antibodies raised against the particular Hsp. tients infected with H. pylori also revealed Hsp60 Performing immunolocalization with sectioned associated with inflamed tissue. 13 These studies bacteria permits further localization of these pro- indicate that Hsp60 is one of the dominant proteins teins among internal compartments. When immu- expressed in situ by H. pylori. nogold electron microscopy was performed on thin An examination of Hsp60 sequences from many INFECTIOUS DISEASES IN OBSTETRICS AND GYNECOLOGY 59 BACTERIAL HSPS IN PA THOGENESIS HOFFMAN AND GARDUNO Hsp60 Mediated Invasion of a HeLa Cell Hsp60 Actin polymerization Lysosomes Rabs Fig. 2. Parasite-directed receptor-mediated endocytosis teria-laden endosome to secondary lysosomes. A feature of of L. pneumophila by HeLa cells. The illustration indicates the specialized endosome in which L. pneumophila replicates that Hsp60 binds to specific receptors on the HeLa cells, is its envelopment by the endoplasmic reticulum. "Rabs" initiating actin polymerization and endocytosis of the bac- indicates several families of GTP-proteins associated with terium into an early endosome. We propose that Hsp60, trafficking activities. GTP guanosine triphosphate; ER interacting with the phagosome membrane, alters signal endoplasmic reticulum. transduction networks that would ordinarily traffic the bac- microbial pathogens deposited in Genbank reveals lated in the laboratory by selection for tolerance to no obvious secretion motifs in this family of highly 0.65% sodium chloride. Mutations conferring so- conserved proteins. Therefore, it has been pro- dium tolerance map to several regions of the chro- posed that the observed surface location of Hsps is mosome containing the dot/icm genes involved in achieved by mechanisms that do not involve secre- facilitating DNA or protein transport. 14,s These tion. For instance, it has been proposed that in H. genes seem to be important in facilitating the sur- pylori, Hsp60 released from naturally lysed bacteria face localization of Hsp60 since avirulent mutants 11 binds to the surface of neighboring bacteria, but appear unable to efficiently localize Hsp60 to the this is not the mechanism by which Hsp60 reaches surface. 9 Several lines of evidence outlined in the 8 the surface of L. pneumophila. Specific studies ad- following sections support the hypothesis that sur- dressing the secretion of Hsp60 by L. pneumophila face-exposed Hsp60 is utilized by L. pneumophila as have not been conducted. However, the observa- an invasin that additionally may alter early events tion that E. coli expressing the L. pneumophila gene associated with organelle trafficking and phagoly- for Hsp60 does not secrete the protein would imply sosomal fusion. that E. coli lacks the machinery used by L. pneumo- phila and perhaps other bacteria to mobilize Hsp60 ADHERENCE AND INVASION to the periplasm or cell surface, s Virulent as well as avirulent strains of L. pneumo- Avirulent mutants of L. pneumophila can be iso- phila are phagocytized by professional phagocytes 60 INFECTIOUS DISEASES IN OBSTETRICS AND GYNECOLOGY BACTERIAL HSPS IN PA THOGENESIS HOFFMAN AND GARDUNO Low acidity High acidity Decreased expression of HSPs Upregulation of HSPs Bacteriaswim in mucus. increase inflammation and release of nutrients Bacteria more adherent. Mucus layer Gastric epithelium Immune response Fig. 3. Illustration of the interactions of H. pylori in the of IL-Ib and IL-12 production by recruited macrophages gastric mucosa. Under conditions of high acidity, such as and interferon-y by activated Th-I T-cells. Under condi- might occur in a gastric or duodenal ulcer, H. pytori Hsps are tions of lower acid (more alkaline pH), repression of Hsp upregulated and both localized on the surface and released. production leads to less adherent bacteria that can be found The increased surface-expressed Hsp60 and Hsp70 pro- throughout the mucus lining of the stomach. From this re- mote attachment to the epithelial cells, which might afford mote location, released
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