Kovit Pattanapanyasat

DC-SIGN (CD209) Mediates Dengue Virus Infection of Human Dendritic Cells

Dengue virus is a single-stranded, enveloped RNA virus that productively infects human dendritic cells (DCs) primarily at the immature stage of their differentiation. We now find that all four serotypes of dengue use DC-SIGN (CD209), a C-type lectin, to infect dendritic cells. THP-1 cells become susceptible to dengue infection after transfection of DC-specific ICAM-3 grabbing nonintegrin (DC-SIGN), or its homologue L-SIGN, whereas the infection of dendritic cells is blocked by anti–DC-SIGN antibodies and not by antibodies to other molecules on these cells. Viruses produced by dendritic cells are infectious for DC-SIGN– and L-SIGN–bearing THP-1 cells and other permissive cell lines. Therefore, DC-SIGN may be considered as a new target for designing therapies that block dengue infection.

Human antibody responses after dengue virus infection are highly cross-reactive to Zika virus

Significance In this study, we address the issue of cross-reactivity between dengue virus (DENV) and Zika virus (ZIKV) by testing sera and plasmablast-derived monoclonal antibodies from dengue patients against ZIKV. We show that both acute and convalescent dengue sera potently bind and neutralize ZIKV and that this cross-reactivity is also evident at the monoclonal level. We also demonstrate in vitro antibody-dependent enhancement of ZIKV infection in the presence of dengue-induced antibodies. Our findings strongly suggest that preexisting dengue antibodies may modulate immune responses to ZIKV infection. These data are timely and highly relevant from a public health standpoint given that a majority of regions currently experiencing Zika virus epidemics are endemic for dengue. Zika virus (ZIKV) is an emerging mosquito-borne flavivirus of significant public health concern. ZIKV shares a high degree of sequence and structural homology compared with other flaviviruses, including dengue virus (DENV), resulting in immunological cross-reactivity. Improving our current understanding of the extent and characteristics of this immunological cross-reactivity is important, as ZIKV is presently circulating in areas that are highly endemic for dengue. To assess the magnitude and functional quality of cross-reactive immune responses between these closely related viruses, we tested acute and convalescent sera from nine Thai patients with PCR-confirmed DENV infection against ZIKV. All of the sera tested were cross-reactive with ZIKV, both in binding and in neutralization. To deconstruct the observed serum cross-reactivity in depth, we also characterized a panel of DENV-specific plasmablast-derived monoclonal antibodies (mAbs) for activity against ZIKV. Nearly half of the 47 DENV-reactive mAbs studied bound to both whole ZIKV virion and ZIKV lysate, of which a subset also neutralized ZIKV. In addition, both sera and mAbs from the dengue-infected patients enhanced ZIKV infection of Fc gamma receptor (FcγR)-bearing cells in vitro. Taken together, these findings suggest that preexisting immunity to DENV may impact protective immune responses against ZIKV. In addition, the extensive cross-reactivity may have implications for ZIKV virulence and disease severity in DENV-experienced populations.

Rapid and Massive Virus-Specific Plasmablast Responses during Acute Dengue Virus Infection in Humans

ABSTRACT Humoral immune responses are thought to play a major role in dengue virus-induced immunopathology; however, little is known about the plasmablasts producing these antibodies during an ongoing infection. Herein we present an analysis of plasmablast responses in patients with acute dengue virus infection. We found very potent plasmablast responses that often increased more than 1,000-fold over the baseline levels in healthy volunteers. In many patients, these responses made up as much 30% of the peripheral lymphocyte population. These responses were largely dengue virus specific and almost entirely made up of IgG-secreting cells, and plasmablasts reached very high numbers at a time after fever onset that generally coincided with the window where the most serious dengue virus-induced pathology is observed. The presence of these large, rapid, and virus-specific plasmablast responses raises the question as to whether these cells might have a role in dengue immunopathology during the ongoing infection. These findings clearly illustrate the need for a detailed understanding of the repertoire and specificity of the antibodies that these plasmablasts produce.

Circulating Red Cell–derived Microparticles in Human Malaria

In patients with falciparum malaria, plasma concentrations of cell-derived microparticles correlate with disease severity. Using flow cytometry, we quantified red blood cell-derived microparticles (RMPs) in patients with malaria and identified the source and the factors associated with production. RMP concentrations were increased in patients with Plasmodium falciparum (n = 29; median, 457 RMPs/μL [range, 13-4,342 RMPs/μL]), Plasmodium vivax (n = 5; median, 409 RMPs/μL [range, 281-503/μL]), and Plasmodium malariae (n = 2; median, 163 RMPs/μL [range, 127-200 RMPs/μL]) compared with those in healthy subjects (n = 11; median, 8 RMPs/μL [range, 3-166 RMPs/μL]; P = .01). RMP concentrations were highest in patients with severe falciparum malaria (P = .01). Parasitized red cells produced >10 times more RMPs than did unparasitized cells, but the overall majority of RMPs still derived from uninfected red blood cells (URBCs). In cultures, RMP production increased as the parasites matured. Hemin and parasite products induced RMP production in URBCs, which was inhibited by N-acetylcysteine, suggesting heme-mediated oxidative stress as a pathway for the generation of RMPs.

Flow cytometric quantitation of red blood cell vesicles in thalassemia

Thalassemia is a hereditary hemolytic anemia caused by mutations in the globin gene complex. Circulatory disturbances including arterial and venous thrombosis have also been noted in these patients. Aggregability of abnormal RBC and the high level of membrane‐derived microparticles stemming from activated platelets and other blood cells are thought to be responsible for the associated thrombotic risk. Destruction of RBC is also thought to be an important pathophysiological consequence, particularly through the formation of circulating vesicles. To our knowledge, there has been no attempt to quantitatively evaluate the number of RBC vesicles in thalassemia. This prompted us to study the level of RBC vesicles in the peripheral blood of thalassemia patients using quantitative flow cytometry.

Dengue Virus Infection Induces Expansion of a CD14+CD16+ Monocyte Population that Stimulates Plasmablast Differentiation

Dengue virus (DENV) infection induces the expansion of plasmablasts, which produce antibodies that can neutralize DENV but also enhance disease upon secondary infection with another DENV serotype. To understand how these immune responses are generated, we used a systems biological approach to analyze immune responses to dengue in humans. Transcriptomic analysis of whole blood revealed that genes encoding proinflammatory mediators and type I interferon-related proteins were associated with high DENV levels during initial symptomatic disease. Additionally, CD14(+)CD16(+) monocytes increased in the blood. Similarly, in a nonhuman primate model, DENV infection boosted CD14(+)CD16(+) monocyte numbers in the blood and lymph nodes. Upon DENV infection in vitro, monocytes upregulated CD16 and mediated differentiation of resting B cells to plasmablasts as well as immunoglobulin G (IgG) and IgM secretion. These findings provide a detailed picture of innate responses to dengue and highlight a role for CD14(+)CD16(+) monocytes in promoting plasmablast differentiation and anti-DENV antibody responses.

Platelet Inhibition by Nitrite Is Dependent on Erythrocytes and Deoxygenation

Background Nitrite is a nitric oxide (NO) metabolite in tissues and blood, which can be converted to NO under hypoxia to facilitate tissue perfusion. Although nitrite is known to cause vasodilation following its reduction to NO, the effect of nitrite on platelet activity remains unclear. In this study, the effect of nitrite and nitrite+erythrocytes, with and without deoxygenation, on platelet activity was investigated. Methodology/Finding Platelet aggregation was studied in platelet-rich plasma (PRP) and PRP+erythrocytes by turbidimetric and impedance aggregometry, respectively. In PRP, DEANONOate inhibited platelet aggregation induced by ADP while nitrite had no effect on platelets. In PRP+erythrocytes, the inhibitory effect of DEANONOate on platelets decreased whereas nitrite at physiologic concentration (0.1 µM) inhibited platelet aggregation and ATP release. The effect of nitrite+erythrocytes on platelets was abrogated by C-PTIO (a membrane-impermeable NO scavenger), suggesting an NO-mediated action. Furthermore, deoxygenation enhanced the effect of nitrite as observed from a decrease of P-selectin expression and increase of the cGMP levels in platelets. The ADP-induced platelet aggregation in whole blood showed inverse correlations with the nitrite levels in whole blood and erythrocytes. Conclusion Nitrite alone at physiological levels has no effect on platelets in plasma. Nitrite in the presence of erythrocytes inhibits platelets through its reduction to NO, which is promoted by deoxygenation. Nitrite may have role in modulating platelet activity in the circulation, especially during hypoxia.

Activated platelet-derived microparticles in thalassaemia.

Thromboembolic complications have been documented in thalassaemia patients. The aggregability of abnormal red blood cells and the high level of membrane‐derived microparticles (MPs) stemming from blood cells are thought to be responsible for the associated thrombotic risk. We investigated the number of MPs, their cellular origin and their procoagulant properties in β‐thalassaemia. Fresh whole blood was simultaneously stained for annexin V, cellular antigens and the known density beads. The procoagulant properties of these phosphatidylserine (PS)‐bearing MPs were also measured by assessing the platelet factor‐3‐like activity in the blood. Flow cytometric results showed that splenectomised β‐thalassaemia/HbE patients had significantly higher levels of PS‐bearing MPs than non‐splenectomised β‐thalassaemia/HbE patients and normal individuals (P < 0·0001). There was a good correlation between PS‐bearing MPs and PS‐bearing platelets, reflecting the existence of chronic platelet activation in β‐thalassaemia/HbE patients (rs = 0·511, P < 0·001). The cellular origin of PS‐bearing MPs showed mostly activated‐platelet origin with adhesion (CD41a/CD62P/CD36). Moreover, the platelet procoagulant activity was higher in splenectomised β‐thalassaemia/HbE patients when compared with non‐splenectomised (P < 0·05) and normal individuals (P < 0·01), and the amount correlated with PS‐bearing MPs (rs = 0·560, P < 0·001). These findings suggest that MPs originate from activated platelets with a potential to aggravate thrombotic events when the numbers are excessive, as is commonly seen in splenectomised β‐thalassaemia/HbE patients.

Performance evaluation of the Alere PIMA CD4 test for monitoring HIV-infected individuals in resource-constrained settings.

Background: Enumeration of CD4+ T-lymphocytes is important in the management of HIV. However, standard laboratory systems based on flow cytometry are expensive, complicated, and thus unavailable to most resource-limited settings where a low-cost and fully automated point-of-care CD4 testing system is required. In attempts to address this issue, a study was conducted to validate the Alere PIMA point-of-care CD4 test. Method: Duplicate values of the absolute number of CD4+ T-lymphocytes in 203 HIV-infected blood samples obtained using the PIMA system were compared with the two predicate single-platform FACSCount and the dual-platform FACSCan (Becton Dickinson Biosciences). Results: The overall absolute CD4+ T-lymphocyte count obtained using the PIMA system correlated highly with the FACSCount (r2 = 0.957; mean bias, -54.2 cells/μL; limit of agreement, -190.9 to +82.5 cells/μL) and the FACSCan (r2 = 0.957; mean bias -44.0 cells/μL; limit of agreement, -179.7 to +91.6 cells/μL). Good correlation and low biases were also observed for samples with CD4+ T-lymphocyte count ranges of 0 to 200 and 0 to 350 cells/μL. Additionally, there was no significant difference in absolute CD4+ T-lymphocyte counts noted between the duplicate samples using the PIMA system. Conclusions: This new point-of-care product is a simple and reliable system and should contribute significantly to the simplification of performing CD4 testing and thus increase access for patients in resource-limited settings. The inability to obtain values for the frequency (%) of CD4+ T-lymphocyte count is one limitation of the PIMA system, the addition of which would be of value for clinical staging or monitoring in HIV-infected pediatric patients.

A novel method to derive amniotic fluid stem cells for therapeutic purposes

BackgroundHuman amniotic fluid stem (hAFS) cells have become an attractive stem cell source for medical therapy due to both their ability to propagate as stem cells and the lack of ethical debate that comes with the use of embryonic stem cells. Although techniques to derive stem cells from amniotic fluid are available, the techniques have limitations for clinical uses, including a requirement of long periods of time for stem cell production, population heterogeneity and xeno-contamination from using animal antibody-coated magnetic beads. Herein we describe a novel isolation method that fits for hAFS derivation for cell-based therapy.Methods and ResultsWith our method, single hAFS cells generate colonies in a primary culture of amniotic fluid cells. Individual hAFS colonies are then expanded by subculturing in order to make a clonal hAFS cell line. This method allows derivation of a substantial amount of a pure stem cell population within a short period of time. Indeed, 108 cells from a clonal hAFS line can be derived in two weeks using our method, while previous techniques require two months. The resultant hAFS cells show a 2-5 times greater proliferative ability than with previous techniques and a population doubling time of 0.8 days. The hAFS cells exhibit typical hAFS cell characteristics including the ability to differentiate into adipogenic-, osteogenic- and neurogenic lineages, expression of specific stem cell markers including Oct4, SSEA4, CD29, CD44, CD73, CD90, CD105 and CD133, and maintenance of a normal karyotype over long culture periods.ConclusionsWe have created a novel hAFS cell derivation method that can produce a vast amount of high quality stem cells within a short period of time. Our technique makes possibility for providing autogenic fetal stem cells and allogeneic cells for future cell-based therapy.