Pilus Adhesin RrgA Interacts with Complement Receptor 3, Thereby Affecting Macrophage Function and Systemic Pneumococcal Disease

10.1128/mBio.00535-12Pneumococcal pili have been shown to influence pneumococcal colonization, disease development, and the inflammatory response in mice. The role of the pilus-associated RrgA adhesin in pneumococcal interactions with murine and human macrophages was investigated. Expression of pili with RrgA enhanced the uptake of pneumococci by murine and human macrophages that was abolished by antibodies to complement receptor 3 (CR3) and not seen in CR3-deficient macrophages. Recombinant RrgA, but not pilus subunit RrgC, promoted CR3-mediated phagocytosis of coated beads by murine and human macrophages. Flow cytometry showed that purified CR3 binds pneumococcal cells expressing RrgA, and purified RrgA was shown to interact with CR3 and its I domain. In vivo, RrgA facilitated spread of pneumococci from the upper airways and peritoneal cavity to the bloodstream. Earlier onset of septicemia and more rapidly progressing disease was observed in wild-type mice compared to CR3-deficient mice challenged intranasally or intraperitoneally with pneumococci. Motility assays and time-lapse video microscopy showed that pneumococcal stimulation of macrophage motility required RrgA and CR3. These findings, together with the observed RrgA-dependent increase of intracellular survivors up to 10 h following macrophage infection, suggest that RrgA-CR3-mediated phagocytosis promotes systemic pneumococcal spread from local sites.IMPORTANCE Streptococcus pneumoniae is a major contributor to morbidity and mortality in infectious diseases globally. Symptomatology is mainly due to pneumococcal interactions with host cells leading to an inflammatory response. However, we still need more knowledge on how pneumococci talk to immune cells and the importance of this interaction. Recently, a novel structure was identified on the pneumococcal surface, an adhesive pilus found in about 30% of clinical pneumococcal isolates. The pilus has been suggested to be important for successful spread of antibiotic-resistant pneumococcal clones globally. Here we sought to identify mechanisms for how the pneumococcal pilin subunit RrgA contributes to disease development by interacting with host immune cells. Our data suggest a new way for how pneumococci may cross talk with phagocytic cells and affect disease progression. An increased understanding of these processes may lead to better strategies for how to treat these common infections.Peer reviewe

Causal Inference Regarding Infectious Aetiology of Chronic Conditions: A Systematic Review

<div><p>Background</p><p>The global burden of disease has shifted from communicable diseases in children to chronic diseases in adults. This epidemiologic shift varies greatly by region, but in Europe, chronic conditions account for 86% of all deaths, 77% of the disease burden, and up to 80% of health care expenditures. A number of risk factors have been implicated in chronic diseases, such as exposure to infectious agents. A number of associations have been well established while others remain uncertain.</p><p>Methods and Findings</p><p>We assessed the body of evidence regarding the infectious aetiology of chronic diseases in the peer-reviewed literature over the last decade. Causality was assessed with three different criteria: First, the total number of associations documented in the literature between each infectious agent and chronic condition; second, the epidemiologic study design (quality of the study); third, evidence for the number of Hill's criteria and Koch's postulates that linked the pathogen with the chronic condition.</p><p>We identified 3136 publications, of which 148 were included in the analysis. There were a total of 75 different infectious agents and 122 chronic conditions. The evidence was strong for five pathogens, based on study type, strength and number of associations; they accounted for 60% of the associations documented in the literature. They were human immunodeficiency virus, hepatitis C virus, <i>Helicobacter pylori</i>, hepatitis B virus, and <i>Chlamydia pneumoniae</i> and were collectively implicated in the aetiology of 37 different chronic conditions. Other pathogens examined were only associated with very few chronic conditions (≤3) and when applying the three different criteria of evidence the strength of the causality was weak.</p><p>Conclusions</p><p>Prevention and treatment of these five pathogens lend themselves as effective public health intervention entry points. By concentrating research efforts on these promising areas, the human, economic, and societal burden arising from chronic conditions can be reduced.</p></div

Number of publications per study type for the respiratory system (year 2001–2010).

<p>Number of publications per study type for the respiratory system (year 2001–2010).</p

Number of publications per study type for neoplasms, blood and blood-forming organs, endocrine, nutritional and metabolic disorders, and nervious system (year 2001–2010).

<p>The chronic conditions were grouped into disease areas according to the highest hierarchy level in the International System for Classification of Diseases (ICD)-10. Associations between infectious agents and chronic conditions belonging to 15 disease areas were identified (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0068861#pone-0068861-g005" target="_blank">Figures 5</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0068861#pone-0068861-g006" target="_blank">6</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0068861#pone-0068861-g007" target="_blank">7</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0068861#pone-0068861-g008" target="_blank">8</a>). The numbers of publications per infectious agent were quantified and, for each infectious agent, the publications were presented according to study type (i.e., systematic reviews, prospective cohort studies and RCTs, retrospective cohort studies, and case-control studies). For each infectious agent and disease area, the total numbers of Hill's criteria and Koch's postulates fulfilled were determined. In the figures, the infectious agents were ranked, first according to the number of Koch's postulates fulfilled and secondly according to the number of Hill's criteria fulfilled. In this dataset, the strongest associations were those between chronic conditions of the circulatory system and <i>C. pneumoniae</i> or <i>T. cruzi</i>, and between chronic conditions of the genitourinary tract and <i>C. trachomatis</i>.</p

Number of publications per study type for skin and connective tissue, muscoskeletal system, genitourinary system, congenital malformations and perinatal blood, unclassified symptoms (year 2001–2010).

<p>Number of publications per study type for skin and connective tissue, muscoskeletal system, genitourinary system, congenital malformations and perinatal blood, unclassified symptoms (year 2001–2010).</p

Number of associations per chronic condition (year 2001–2010).

<p>There were 122 chronic conditions identified in the current study. At least five associations were identified for each of the chronic conditions displayed, and the number of associations per chronic condition was disaggregated according to the class of infectious agent (i.e. bacteria, viruses, fungi, and parasites). The top-five chronic conditions identified in this data set were chronic rhinosinusitis, cirrhosis, hepatocellular carcinoma, bronchiectasis, and chronic liver disease. Viruses were most frequently associated with these chronic conditions, followed by bacteria, fungi, and parasites.</p

Percentage of publications per disease area (year 2001–2010).

<p>The chronic conditions were grouped into disease areas according to the highest hierarchy level in the ICD-10, and are displayed in that order. As certain publications described several individual associations, the classification into disease areas is not exclusive. Thus, the total percentage does not sum up to 100%. The disease areas where the highest numbers of publications were identified were the digestive system, neoplasms, the circulatory system, the respiratory system, and the nervous system.</p

Number of associations described per infectious agent (year 2001–2010).

<p>There were 75 infectious agents identified in this study. At least five associations to one or more disease areas were identified for each of the infectious agents displayed. The number of associations per infectious agent was disaggregated into disease areas based on the highest hierarchy level in the ICD-10, and is displayed above the bars. The infectious agents for which the highest numbers of associations were described were HIV, HCV, <i>Helicobacter spp.</i>, HBV, and <i>C. pneumoniae</i>. Generally, viruses tended to be associated with a high number of disease areas, followed by bacteria, parasites, and fungi.</p

Flow diagram outlining included and excluded publications (year 2001–2010).

<p>A protocol was devised for the systematic study, and the searches were performed in the MEDLINE®, Embase®, Cochrane Reviews and Cochrane Clinical Trials databases. The following inclusion criteria were applied: Infectious agent implicated as a cause or a co-factor of a chronic condition (i.e. disease, disabilities and sequelae that last at least three months); publication in English between 2001 and 2010; study types, i.e. SRs; RCTs, cohort studies, cross-sectional studies, case-control studies, case studies/case series/case reports, literature reviews, or pathological assessments of diseased material. Exclusion criteria were: Infectious agents described as triggers to the chronic condition; non-English language; publication year before 2001; study type, i.e. other studies than those outlines in the inclusion criteria above (including animal studies). In total, 3136 publications were identified in the systematic searches in the databases, and 148 publications were finally included in the analysis. Citations were first screened by two independent reviewers (‘first pass’). Full-text copies of all references that could potentially meet the eligibility were then screened by two independent reviewers (‘second pass’). The data presented in the publications included after this stage were extracted by two independent reviewers.</p

TLR7 contributes to the rapid progression but not to the overall fatal outcome of secondary pneumococcal disease following influenza A virus infection.

Increased risk for bacterial superinfections substantially contributes to the mortality caused by influenza A virus (IAV) epidemics. While the mechanistic basis for this lethal synergism is still insufficiently understood, immune modulation through the viral infection has been shown to be involved. Since the pattern-recognition receptor (PRR) toll-like receptor 7 (TLR7) is a major sensor for the viral genome, we studied how IAV recognition by TLR7 influences the development of secondary pneumococcal infection. In a mouse model of IAV, TLR7-deficient hosts induced a potent antiviral response and showed unchanged survival. In secondary pneumococcal infection during acute influenza, TLR7ko mice showed a fatal outcome similar to wild-type (WT) hosts, despite significantly delayed disease progression. Also, when bacterial superinfection occurred after virus clearance, WT and TLR7-deficient hosts showed similar mortality, even though we found the phagocytic activity of alveolar macrophages isolated from IAV-pre-infected hosts to be enhanced in TLR7ko over WT mice. Thus, we show that a virus-sensing PRR modulates the progression of secondary pneumococcal infection following IAV. However, the fatal overall outcome in WT as well as TLR7ko hosts suggests that processes distinct from TLR7-triggering override the contribution of this single PRR