Porphyromonas gingivalis–dendritic cell interactions: consequences for coronary artery disease

An estimated 80 million US adults have one or more types of cardiovascular diseases. Atherosclerosis is the single most important contributor to cardiovascular diseases; however, only 50% of atherosclerosis patients have currently identified risk factors. Chronic periodontitis, a common inflammatory disease, is linked to an increased cardiovascular risk. Dendritic cells (DCs) are potent antigen presenting cells that infiltrate arterial walls and may destabilize atherosclerotic plaques in cardiovascular disease. While the source of these DCs in atherosclerotic plaques is presently unclear, we propose that dermal DCs from peripheral inflamed sites such as CP tissues are a potential source. This review will examine the role of the opportunistic oral pathogen Porphyromonas gingivalis in invading DCs and stimulating their mobilization and misdirection through the bloodstream. Based on our published observations, combined with some new data, as well as a focused review of the literature we will propose a model for how P. gingivalis may exploit DCs to gain access to systemic circulation and contribute to coronary artery disease. Our published evidence supports a significant role for P. gingivalis in subverting normal DC function, promoting a semimature, highly migratory, and immunosuppressive DC phenotype that contributes to the inflammatory development of atherosclerosis and, eventually, plaque rupture

The Native 67-Kilodalton Minor Fimbria of Porphyromonas gingivalis Is a Novel Glycoprotein with DC-SIGN-Targeting Motifs▿

We recently reported that the oral mucosal pathogen Porphyromonas gingivalis, through its 67-kDa Mfa1 (minor) fimbria, targets the C-type lectin receptor DC-SIGN for invasion and persistence within human monocyte-derived dendritic cells (DCs). The DCs respond by inducing an immunosuppressive and Th2-biased CD4+ T-cell response. We have now purified the native minor fimbria by ion-exchange chromatography and sequenced the fimbria by tandem mass spectrometry (MS/MS), confirming its identity and revealing two putative N-glycosylation motifs as well as numerous putative O-glycosylation sites. We further show that the minor fimbria is glycosylated by ProQ staining and that glycosylation is partially removed by treatment with β(1-4)-galactosidase, but not by classic N- and O-linked deglycosidases. Further monosaccharide analysis by gas chromatography-mass spectrometry (GC-MS) confirmed that the minor fimbria contains the DC-SIGN-targeting carbohydrates fucose (1.35 nmol/mg), mannose (2.68 nmol/mg), N-acetylglucosamine (2.27 nmol/mg), and N-acetylgalactosamine (0.652 nmol/mg). Analysis by transmission electron microscopy revealed that the minor fimbria forms fibers approximately 200 nm in length that could be involved in targeting or cross-linking DC-SIGN. These findings shed further light on molecular mechanisms of invasion and immunosuppression by this unique mucosal pathogen

Effects of Age, Hemoglobin Type and Parasite Strain on IgG Recognition of <i>Plasmodium falciparum</i>–Infected Erythrocytes in Malian Children

<div><p>Background</p><p>Naturally-acquired antibody responses to antigens on the surface of <i>Plasmodium falciparum</i>-infected red blood cells (iRBCs) have been implicated in antimalarial immunity. To profile the development of this immunity, we have been studying a cohort of Malian children living in an area with intense seasonal malaria transmission.</p> <p>Methodology/Principal Findings</p><p>We collected plasma from a sub-cohort of 176 Malian children aged 3-11 years, before (May) and after (December) the 2009 transmission season. To measure the effect of hemoglobin (Hb) type on antibody responses, we enrolled age-matched HbAA, HbAS and HbAC children. To quantify antibody recognition of iRBCs, we designed a high-throughput flow cytometry assay to rapidly test numerous plasma samples against multiple parasite strains. We evaluated antibody reactivity of each plasma sample to 3 laboratory-adapted parasite lines (FCR3, D10, PC26) and 4 short-term-cultured parasite isolates (2 Malian and 2 Cambodian). 97% of children recognized ≥1 parasite strain and the proportion of IgG responders increased significantly during the transmission season for most parasite strains. Both strain-specific and strain-transcending IgG responses were detected, and varied by age, Hb type and parasite strain. In addition, the breadth of IgG responses to parasite strains increased with age in HbAA, but not in HbAS or HbAC, children.</p> <p>Conclusions/Significance</p><p>Our assay detects both strain-specific and strain-transcending IgG responses to iRBCs. The magnitude and breadth of these responses varied not only by age, but also by Hb type and parasite strain used. These findings indicate that studies of acquired humoral immunity should account for Hb type and test large numbers of diverse parasite strains.</p> </div

Strain-specific innate immune signaling pathways determine malaria parasitemia dynamics and host mortality

Intramural Research Program of the Division of Intramural Research at the NIAID; National Institutes of Health (NIH); National Cancer Institute; NIH [R01CA090327, R01CA101795]; China Scholarship Council (CSC)Malaria infection triggers vigorous host immune responses; however, the parasite ligands, host receptors, and the signaling pathways responsible for these reactions remain unknown or controversial. Malaria parasites primarily reside within RBCs, thereby hiding themselves from direct contact and recognition by host immune cells. Host responses to malaria infection are very different from those elicited by bacterial and viral infections and the host receptors recognizing parasite ligands have been elusive. Here we investigated mouse genome-wide transcriptional responses to infections with two strains of Plasmodium yoelii (N67 and N67C) and discovered differences in innate response pathways corresponding to strain-specific disease phenotypes. Using in vitro RNAi-based gene knockdown and KO mice, we demonstrated that a strong type I IFN (IFN-I) response triggered by RNA polymerase III and melanoma differentiation-associated protein 5, not Toll-like receptors (TLRs), binding of parasite DNA/RNA contributed to a decline of parasitemia in N67-infected mice. We showed that conventional dendritic cells were the major sources of early IFN-I, and that surface expression of phosphatidylserine on infected RBCs might promote their phagocytic uptake, leading to the release of parasite ligands and the IFN-I response in N67 infection. In contrast, an elevated inflammatory response mediated by CD14/TLR and p38 signaling played a role in disease severity and early host death in N67C-infected mice. In addition to identifying cytosolic DNA/RNA sensors and signaling pathways previously unrecognized in malaria infection, our study demonstrates the importance of parasite genetic backgrounds in malaria pathology and provides important information for studying human malaria pathogenesis

Breadth of IgG responses to parasite strains stratified by season, Hb type and age.

<p>The number of parasite strains (range, 0-7) recognized by IgG were counted and stratified by season, Hb type and age. <b>a</b>, Tukey whisker plots showing the total number of parasite strains recognized by IgG in paired plasma samples taken before and after the 2009 transmission season. p-values were calculated using Wilcoxon matched-pairs signed rank test. **p<0.01. <b>b</b>, <b>c</b>, Tukey whisker plots showing the total number of parasite strains recognized by IgG before (<b>b</b>) and after (<b>c</b>) the 2009 transmission season, stratified by age and Hb type. p-values were calculated using Kruskal-Wallis test followed by Dunn’s multiple comparison test. *p<0.05, **p<0.01, ***p<0.001.</p

Effect of Hb type on IgG recognition of different parasite strains.

<p>The proportions of children responding to each parasite strain were compared between Hb types, before and after the transmission season. The age effect at each time point was evaluated using Chi-square likelihood ratio test; significant findings were then confirmed by Odds ratio test. The seasonal effect of each Hb type was evaluated using Fisher’s exact test. *p<0.05, **p<0.01, ***p<0.001. Error bars shown are the upper 95% Confidence Interval for the % responder estimates.</p

The breadth of IgG responses to parasite strains correlates with increased IgG titers to merozoite antigens.

<p>IgG titers to 4 merozoite antigens (AMA-1, EBA-175, MSP-1, MSP-2) were measured in plasma obtained before the transmission season, and stratified by the total number of parasite strains recognized by IgG. Tukey whisker plots are shown. IgG titers were compared using Kruskal-Wallis test followed by Dunn’s multiple comparison test. *p<0.05. The numbers of children recognizing 0-2, 3, 4, 5 and 6-7 parasite strains were 45, 34, 32, 36 and 30.</p

Effect of age on IgG recognition of different parasite strains.

<p>The proportions of children responding to each parasite strain were compared between age groups, before and after the transmission season. The age effect at each time point was evaluated using Chi-square likelihood ratio test; significant findings were then confirmed by Odds ratio test. The seasonal effect in each age group was evaluated using Fisher’s exact test. *p<0.05, **p<0.01, ***p<0.001. Error bars shown are the upper 95% Confidence Interval for the % responder estimates.</p