TF-FVIIa PAR2-ß-Arrestin Signaling Sustains Organ Dysfunction in Coxsackievirus B3 Infection of Mice.

BACKGROUND: Accumulating evidence implicates the activation of G-protein-coupled PARs (protease-activated receptors) by coagulation proteases in the regulation of innate immune responses. METHODS: Using mouse models with genetic alterations of the PAR2 signaling platform, we have explored contributions of PAR2 signaling to infection with coxsackievirus B3, a single-stranded RNA virus provoking multiorgan tissue damage, including the heart. RESULTS: We show that PAR2 activation sustains correlates of severe morbidity-hemodynamic compromise, aggravated hypothermia, and hypoglycemia-despite intact control of the virus. Following acute viral liver injury, canonical PAR2 signaling impairs the restoration process associated with exaggerated type I IFN (interferon) signatures in response to viral RNA recognition. Metabolic profiling in combination with proteomics of liver tissue shows PAR2-dependent reprogramming of liver metabolism, increased lipid droplet storage, and gluconeogenesis. PAR2-sustained hypodynamic compromise, reprograming of liver metabolism, as well as imbalanced IFN responses are prevented in ß-arrestin coupling-deficient PAR2 C-terminal phosphorylation mutant mice. Thus, wiring between upstream proteases and immune-metabolic responses results from biased PAR2 signaling mediated by intracellular recruitment of ß-arrestin. Importantly, blockade of the TF (tissue factor)-FVIIa (coagulation factor VIIa) complex capable of PAR2 proteolysis with the NAPc2 (nematode anticoagulant protein c2) mitigated virus-triggered pathology, recapitulating effects seen in protease cleavage-resistant PAR2 mice. CONCLUSIONS: These data provide insights into a TF-FVIIa signaling axis through PAR2-ß-arrestin coupling that is a regulator of inflammation-triggered tissue repair and hemodynamic compromise in coxsackievirus B3 infection and can potentially be targeted with selective coagulation inhibitors.

Rotaviruses in Wild Ungulates from Germany, 2019-2022.

Rotavirus A (RVA) is an important cause of diarrhea in humans and animals. However, RVA in wild animals has only scarcely been investigated so far. Here, the presence of RVA in wild ungulates hunted between 2019 and 2022 in Brandenburg, Germany, was investigated using real-time RT-PCR and sequencing of RT-PCR products. By analyzing intestinal contents, RVA-RNA was detected in 1.0% (2/197) of wild boar (Sus scrofa), 1.3% (2/152) of roe deer (Capreolus capreolus), and 2.1% (2/95) of fallow deer (Dama dama) but not in 28 red deer (Cervus elaphus) samples. Genotyping identified G3P[13] strains in wild boar, which were closely related to previously described pig and wild boar strains. Genotype G10P[15] strains, closely related to strains from roe deer, sheep, or cattle, were found in roe deer. The strains of fallow deer represented genotype G3P[3], clustering in a group containing different strains from several hosts. The results indicated a low prevalence of RVA in wild ungulates in Germany. Associations of specific genotypes with certain ungulate species seem to exist but should be confirmed by analyses of more samples in the future.

Comparison of Extraction Methods for the Detection of Tick-Borne Encephalitis Virus RNA in Goat Raw Milk and Cream Cheese.

Infection with the tick-borne encephalitis virus (TBEV) can cause meningitis, meningoencephalitis and myelitis in humans. TBEV is an enveloped RNA virus of the family Flaviviridae, which is mostly transmitted via tick bites. However, transmission by consumption of virus-contaminated goat raw milk and goat raw milk products has also been described. Only a few methods have been reported for the detection of TBEV in food so far. Here, we compare different virus extraction methods for goat raw milk and goat raw milk cream cheese and subsequent detection of TBEV-RNA by RT-qPCR. Langat virus (LGTV), a naturally attenuated TBEV strain, was used for artificial contamination experiments. Mengovirus and the human coronavirus 229E were compared to assess their suitability to serve as internal process controls. Out of three tested extraction protocols for raw milk, sample centrifugation followed by direct RNA extraction from the aqueous interphase yielded the best results, with a recovery rate (RR) of 31.8 ± 4.9% for LGTV and a detection limit of 6.7 × 103 LGTV genome copies/ml. Out of two methods for cream cheese, treatment of the samples with TRI Reagent® and chloroform prior to RNA extraction showed the best RR of 4.7 ± 1.6% for LGTV and a detection limit of 9.4 × 104 LGTV genome copies/g. RRs of Mengovirus and LGTV were similar for both methods; therefore, Mengovirus is suggested as internal process control virus. The developed methods may be useful for screening or surveillance studies, as well as in outbreak investigations.

[Hepatitis E virus-a zoonotic virus: distribution, transmission pathways, and relevance for food safety]. / Das Hepatitis-E-Virus ­ ein zoonotisches Virus: Verbreitung, Übertragungswege und Bedeutung für die Lebensmittelsicherheit.

The hepatitis E virus (HEV) is an etiological agent of acute hepatitis in humans. In addition, chronic infections resulting in fatal liver cirrhosis currently emerge in immunosuppressed transplant patients. The number of notified hepatitis E cases in Germany has steeply increased in recent years. Here, genotype 3, which can be zoonotically transmitted from animals to humans, is predominant. The main reservoirs are pigs and wild boars, which show no signs of infection. In this article, the distribution of HEV in animals in Germany, possible transmission pathways, and especially the importance of food as a transmission vehicle are presented based on the current scientific literature.HEV is widely spread among domestic pigs and wild boars in Germany and the virus is mainly transmitted by direct contact or by consumption of food produced from those animals. However, if HEV RNA is detected in specific food it is often unclear whether the contained virus is still infectious or inactivated by the conditions during production. Recent studies indicate a high stability of HEV against different physicochemical conditions, whereas - among others - the virus can be efficiently inactivated by heating. Therefore, proper heating of pork meat and liver prior to consumption in general is recommended. For risk groups, avoiding shortly cured raw sausages is an additional suggestion.Further research is necessary to identify relevant risk food products, to investigate alternative transmission pathways, and to develop efficient measures in order to reduce or prevent zoonotic transmissions of the virus in future.

Mitigated viral myocarditis in A/J mice by the immunoproteasome inhibitor ONX 0914 depends on inhibition of systemic inflammatory responses in CoxsackievirusB3 infection.

A preclinical model of troponin I-induced myocarditis (AM) revealed a prominent role of the immunoproteasome (ip), the main immune cell-resident proteasome isoform, in heart-directed autoimmunity. Viral infection of the heart is a known trigger of cardiac autoimmunity, with the ip enhancing systemic inflammatory responses after infection with a cardiotropic coxsackievirusB3 (CV). Here, we used ip-deficient A/J-LMP7-/- mice to investigate the role of ip-mediated effects on adaptive immunity in CV-triggered myocarditis and found no alteration of the inflammatory heart tissue damage or cardiac function in comparison to wild-type controls. Aiming to define the impact of the systemic inflammatory storm under the control of ip proteolysis during CV infection, we targeted the ip in A/J mice with the inhibitor ONX 0914 after the first cycle of infection, when systemic inflammation has set in, well before cardiac inflammation. During established acute myocarditis, the ONX 0914 treatment group had the same reduction in cardiac output as the controls, with inflammatory responses in heart tissue being unaffected by the compound. Based on these findings and with regard to the known anti-inflammatory role of ONX 0914 in CV infection, we conclude that the efficacy of ip inhibitors for CV-triggered myocarditis in A/J mice relies on their immunomodulatory effects on the systemic inflammatory reaction.

Interlaboratory Validation of a Detection Method for Hepatitis E Virus RNA in Pig Liver.

BACKGROUND: In the last years, the number of notified hepatitis E cases in humans has continuously increased in Europe. Foodborne infection with the zoonotic hepatitis E virus (HEV) genotype 3 is considered the major cause of this disease. Undercooked liver and raw sausages containing the liver of pigs and wild boar are at high risk of containing HEV. However, so far, no standardized method for the detection of HEV-RNA in pig liver is available. METHODS: An international collaborative study on method reproducibility involving 11 laboratories was performed for an HEV-RNA detection method, which consists of steps of sample homogenization, RNA extraction and real-time RT-PCR detection, including a process control. Naturally contaminated pork liver samples containing two different amounts of HEV and a HEV-negative pork liver sample were tested by all laboratories using the method. RESULTS: Valid results were retrieved from 10 laboratories. A specificity of 100% and a sensitivity of 79% were calculated for the method. False negative results were only retrieved from the sample containing very low HEV amounts near the detection limit. CONCLUSIONS: The results show that the method is highly specific, sufficiently sensitive and robust for use in different laboratories. The method can, therefore, be applied to routine food control as well as in monitoring studies.

Interlaboratory Validation of a Method for Hepatitis E Virus RNA Detection in Meat and Meat Products.

Increasing numbers of hepatitis E cases are currently recognized in many European countries. The zoonotic hepatitis E virus (HEV) genotype 3 mainly circulates in domestic pigs and wild boars, and can be transmitted to humans via consumption of insufficiently heated meat or meat products produced from those animals. Here, a detailed protocol for detection of HEV RNA in meat products is provided, which is based on the method originally described by Szabo et al. (Intl J Food Microbiol 215:149-156, 2015). It consists of a TRI Reagent®/chloroform-based food matrix homogenization, a silica bead-based RNA extraction and a real-time RT-PCR-based RNA detection. The method was further validated in a ring trial with nine independent laboratories using pork liver sausage samples artificially contaminated with different amounts of HEV. The results indicate sufficient sensitivity, specificity, and accuracy of the method for its broad future use in survey studies, routine food control or outbreak investigations.

The immunoproteasome-specific inhibitor ONX 0914 reverses susceptibility to acute viral myocarditis.

Severe heart pathology upon virus infection is closely associated with the immunological equipment of the host. Since there is no specific treatment available, current research focuses on identifying new drug targets to positively modulate predisposing immune factors. Utilizing a murine model with high susceptibility to coxsackievirus B3-induced myocarditis, this study describes ONX 0914-an immunoproteasome-specific inhibitor-as highly protective during severe heart disease. Represented by reduced heart infiltration of monocytes/macrophages and diminished organ damage, ONX 0914 treatment reversed fulminant pathology. Virus-induced immune response features like overwhelming pro-inflammatory cytokine and chemokine production as well as a progressive loss of lymphocytes all being reminiscent of a sepsis-like disease course were prevented by ONX 0914. Although the viral burden was only minimally affected in highly susceptible mice, resulting maintenance of immune homeostasis improved the cardiac output, and saved animals from severe illness as well as high mortality. Altogether, this could make ONX 0914 a potent drug for the treatment of severe virus-mediated inflammation of the heart and might rank immunoproteasome inhibitors among drugs for preventing pathogen-induced immunopathology.

Inhibition of chymotryptic-like standard proteasome activity exacerbates doxorubicin-induced cytotoxicity in primary cardiomyocytes.

The anthracycline doxorubicin (DOX) is a potent anticancer agent for multiple myeloma (MM). A major limitation of this drug is the induction of death in cardiomyocytes leading to heart failure. Here we report on the role of the ubiquitin-proteasome system (UPS) as a critical surveillance pathway for preservation of cell vitality counteracting DOX treatment. Since in addition to DOX also suppression of proteasome activity is a rational therapeutic strategy for MM, we examined how small molecular compounds with clinically relevant proteasome subunit specificity affect DOX cytotoxicity. We found that during DOX-treatment, the activity of the ß5 standard proteasome subunit is crucial for limiting off-target cytotoxicity in primary cardiomyocytes. In contrast, we demonstrate that the ß5 equivalent LMP7 of the immunoproteasome represents a safe target for subunit-specific inhibitors in DOX-exposed cardiomyocytes. Neither inhibition of LMP7 in primary cardiomyocytes nor genetic ablation of LMP7 in heart tissue influenced the development of DOX cardiotoxicity. Our results indicate that as compared to compounds like carfilzomib, which target both the ß5 standard proteasome and the LMP7 immunoproteasome subunit, immunoproteasome-specific inhibitors with known anti-tumor capacity for MM cells might be advantageous for reducing cardiomyocyte death, when a combination therapy with DOX is envisaged.

The immunoproteasome controls the availability of the cardioprotective pattern recognition molecule Pentraxin3.

Cardiomyocyte death as a result of viral infection is an excellent model for dissecting the inflammatory stress response that occurs in heart tissue. We reported earlier that a specific proteasome isoform, the immunoproteasome, prevents exacerbation of coxsackievirus B3 (CVB3)-induced myocardial destruction and preserves cell vitality in heart tissue inflammation. Following the aim to decipher molecular targets of immunoproteasome-dependent proteolysis, we investigated the function and regulation of the soluble PRR Pentraxin3 (PTX3). We show that the ablation of PTX3 in mice aggravated CVB3-triggered inflammatory injury of heart tissue, without having any significant effect on viral titers. Thus, there might be a role of PTX3 in preventing damage-associated molecular pattern-induced cell death. We found that the catalytic activity of the immunoproteasome subunit LMP7 regulates the timely availability of factors controlling PTX3 production. We report on immunoproteasome-dependent alteration of ERK1/2 and p38MAPKs, which were both found to be involved in PTX3 expression control. Our finding of a cardioprotective function of immunoproteasome-dependent PTX3 expression revealed a crucial mechanism of the stress-induced damage response in myocardial inflammation. In addition to antigen presentation and cytokine production, proteolysis by the immunoproteasome can also regulate the innate immune response during viral infection.

Ubiquitin-like protein ISG15 (interferon-stimulated gene of 15 kDa) in host defense against heart failure in a mouse model of virus-induced cardiomyopathy.

BACKGROUND: Common causative agents in the development of inflammatory cardiomyopathy include cardiotropic viruses such as coxsackievirus B3 (CVB3). Here, we investigated the role of the ubiquitin-like modifier interferon-stimulated gene of 15 kDa (ISG15) in the pathogenesis of viral cardiomyopathy. METHODS AND RESULTS: In CVB3-infected mice, the absence of protein modification with ISG15 was accompanied by a profound exacerbation of myocarditis and by a significant increase in mortality and heart failure. We found that ISG15 in cardiomyocytes contributed significantly to the suppression of viral replication. In the absence of an intact ISG15 system, virus titers were markedly elevated by postinfection day 8, and viral RNA persisted in ISG15(-/-) mice at postinfection day 28. Ablation of the ISG15 protein modification system in CVB3 infection predisposed mice to long-term disease with deposition of collagen fibers, all leading to inflammatory cardiomyopathy. We found that ISG15 acts as part of the intrinsic immunity in cardiomyocytes and detected no significant effects of ISG15 modification on the cellular immune response. ISG15 modification of CVB3 2A protease counterbalanced CVB3-induced cleavage of the host cell eukaryotic initiation factor of translation eIF4G in cardiomyocytes, thereby counterbalancing the shutoff of host cell translation in CVB3 infection. We demonstrate that ISG15 suppressed infectious virus yield in human cardiac myocytes and the induction of ISG15 in patients with viral cardiomyopathy. CONCLUSIONS: The ISG15 conjugation system represents a critical innate response mechanism in cardiomyocytes to fight the battle against invading pathogens, limiting inflammatory cardiomyopathy, heart failure, and death. Interference with the ISG15 system might be a novel therapeutic approach in viral cardiomyopathy.

In vivo ablation of type I interferon receptor from cardiomyocytes delays coxsackieviral clearance and accelerates myocardial disease.

UNLABELLED: Acute coxsackievirus B3 (CVB3) infection is one of the most prevalent causes of acute myocarditis, a disease that frequently is identified only after the sudden death of apparently healthy individuals. CVB3 infects cardiomyocytes, but the infection is highly focal, even in the absence of a strong adaptive immune response, suggesting that virus spread within the heart may be tightly constrained by the innate immune system. Type I interferons (T1IFNs) are an obvious candidate, and T1IFN receptor (T1IFNR) knockout mice are highly susceptible to CVB3 infection, succumbing within a few days of challenge. Here, we investigated the role of T1IFNs in the heart using a mouse model in which the T1IFNR gene can be ablated in vivo, specifically in cardiomyocytes. We found that T1IFN signaling into cardiomyocytes contributed substantially to the suppression of viral replication and infectious virus yield in the heart; in the absence of such signaling, virus titers were markedly elevated by day 3 postinfection (p.i.) and remained high at day 12 p.i., a time point at which virus was absent from genetically intact littermates, suggesting that the T1IFN-unresponsive cardiomyocytes may act as a safe haven for the virus. Nevertheless, in these mice the myocardial infection remained highly focal, despite the cardiomyocytes' inability to respond to T1IFN, indicating that other factors, as yet unidentified, are sufficient to prevent the more widespread dissemination of the infection throughout the heart. The absence of T1IFN signaling into cardiomyocytes also was accompanied by a profound acceleration and exacerbation of myocarditis and by a significant increase in mortality. IMPORTANCE: Acute coxsackievirus B3 (CVB3) infection is one of the most common causes of acute myocarditis, a serious and sometimes fatal disease. To optimize treatment, it is vital that we identify the immune factors that limit virus spread in the heart and other organs. Type I interferons play a key role in controlling many virus infections, but it has been suggested that they may not directly impact CVB3 infection within the heart. Here, using a novel line of transgenic mice, we show that these cytokines signal directly into cardiomyocytes, limiting viral replication, myocarditis, and death.

Coxsackievirus B3 infects the bone marrow and diminishes the restorative capacity of erythroid and lymphoid progenitors.

Coxsackievirus B3 (CVB3) is known to infect stem cells in the neonatal central nervous system. Here, we evaluated the effects of CVB3 infection on the major source and repository of stem cells, the bone marrow (BM). Viral genome was detectable in BM within 24 h of infection, and productive infection of BM cells was evident, peaking at 48 h postinfection (p.i.), when ∼1 to 2% of BM cells produced infectious virus particles. Beginning at 2 to 3 days p.i., a dramatic and persistent loss of immature erythroid cells, B and T lymphocytes, and neutrophils was observed in BM and, by day 3 to 4 p.i., the femoral BM stroma was largely destroyed. Analysis of peripheral blood revealed a modest neutrophilia, a loss of reticulocytes, and a massive lymphopenia. The abundance of multipotent progenitor cells (Lin(-)/c-kit(+)/Flt3(+)) in BM declined ∼10-fold during CVB3 infection and, consistent with a deficiency of primitive hematopoietic progenitors, serum levels of the hematopoietic growth factor Flt3 ligand were dramatically elevated. Therefore, we analyzed the regenerative capacity of BM from CVB3-infected mice. Granulocyte/macrophage progenitors displayed a relatively normal proliferative ability, consistent with the fact that the peripheral blood level of neutrophils-which are very short-lived cells-remained high throughout infection. However, erythroid and lymphoid hematopoietic progenitors in BM from CVB3-infected mice showed a markedly reduced colony-forming capacity, consonant with the observed loss of both lymphocytes and immature erythroid cells/reticulocytes from the BM and peripheral blood. In summary, CVB3 infects the BM and exerts differential effects on the various hematopoietic progenitor populations.

Inhibition of fatty acid synthase by amentoflavone reduces coxsackievirus B3 replication.

Coxsackievirus B3 (CVB3) is a human pathogen that causes acute and chronic infections, but an antiviral drug to treat these diseases has not yet been developed for clinical use. Several intracellular pathways are altered to assist viral transcription, RNA replication, and progeny release. Among these, fatty acid synthase (FAS) expression is increased. In order to test the potential of FAS inhibition as an anti-CVB3 strategy, several experiments were performed, including studies on the correlation of CVB3 replication and FAS expression in human Raji cells and an analysis of the time and dose dependence of the antiviral effect of FAS inhibition due to treatment with amentoflavone. The results demonstrate that CVB3 infection induces an up-regulation of FAS expression already at 1 h postinfection (p.i.). Incubation with increasing concentrations of amentoflavone inhibited CVB3 replication significantly up to 8 h p.i. In addition, suppression of p38 MAP kinase activity by treatment with SB239063 decreased FAS expression as well as viral replication. These data provide evidence that FAS inhibition via amentoflavone administration might present a target for anti-CVB3 therapy.

Inhibition of nuclear factor kappa B activation reduces Coxsackievirus B3 replication in lymphoid cells.

Interactions between viral replication machineries and host cell metabolism display interesting information how certain viruses capitalize cellular pathways to support progeny production. Among those pathogens, Coxsackievirus B3 (CVB3) has been identified to manipulate intracellular signaling very comprehensively. Next to others, this human pathogenic virus causes acute and chronic forms of myocarditis, pancreatitis, and meningitis. Here, activation of nuclear factor kappa B (NFκB) signaling appears to be involved in successful infection. Viral replication is not restricted to solid organs but involves susceptible immune cells as well. In the present study, p65 phosphorylation as one aspect of NFκB activation and inhibition via BAY 11-7085 administration was analyzed in the context of CVB3 replication in lymphoid cells. During CVB3 infection, an up-regulation of p65 translation is detectable, which is accompanied by noticeable phosphorylation. Inhibition of NFκB signaling reduces viral replication in a dose- and time-dependent manner. Taken together, these results indicate that during CVB3 replication in human and murine lymphoid cells, NFκB signaling is activated and facilitates viral replication. Therefore, antiviral strategies to target such central cellular signaling pathways may represent potential possibilities for the development of new virostatica.

Analysis of different DNA vaccines for protection of experimental influenza A virus infection.

Influenza viruses cause acute respiratory infections in humans that result in significant excessive morbidity and mortality rates every year. Current vaccines are limited in several aspects, including laborious manufacturing technology, non-sufficient efficacy, and time-consuming adjustments to new emerging virus variants. An alternative vaccine approach utilizes plasmid DNA encoding influenza virus antigens. Previous experiments have evaluated the protective efficacy of DNA vaccines expressing variable as well as conserved antigens. In this present study, several different combinations of influenza A virus (IAV) HA, NA, M1, M2, NS1, NS2, and NP sequences were cloned into the plasmid pVIVO, which allows the independent expression of two genes separately. These DNA vaccines were administered to induce protection against a lethal IAV infection, and to reduce immunopathology in lung tissue of surviving animals. The highest efficacy was provided by vaccines expressing HA and NA, as well as a mixture of plasmids encoding HA, NA, M1, M2, NS1, NS2, and NP (Mix). Three days post-infection, more than a 99.99% reduction of viral load and no inflammation was achieved in lung tissue of pVIVO/HA-NA-vaccinated mice. Animals vaccinated with pVIVO/HA-NA, pVIVO/HA-M2, or vaccine Mix, survived a lethal challenge with minor or no obvious pathologic abnormities in the lungs. All other surviving mice revealed extensive changes in the lung tissue, indicating possibly an ongoing bronchiolitis obliterans. In addition, pVIVO/HA-NA and the vaccine Mix were also protective against a heterologous IAV infection. Taken together, next to all combinations of different DNA vaccines, the intramuscular application of pVIVO/HA-NA was the most efficient procedure to decrease virus replication and to prevent immunopathology in lung tissue of IAV-infected mice.

Therapy of experimental influenza virus infection with pyrrolidine dithiocarbamate.

The search for new antiviral strategies to treat influenza A virus (IAV) infections is one major international health care activity. Hereby, the IAV-caused misuse of cellular nuclear factor kappa B (NF-κB) signaling pathways in infected cells represents one target for antiviral therapy. In the present study, pyrrolidine dithiocarbamate (PDTC), which is known as an antioxidant and as an inhibitor of IAV-induced NF-κB activation, was studied in vivo. After the antiviral activity of PDTC was confirmed in MDCK cells, mice-infected with the mouse-adapted strain of IAV A/PR/8/34 (H1N1)-were treated intraperitoneally simultaneously with PDTC (75, 150, 200 mg/kg body weight). The influence of PDTC administrations was evaluated on viral replication and inflammatory reactions in lung tissue up to 14 days postinfection (p. i.). This therapy increased survival up to 80% and reduced IAV-caused weight loss and viral replication in lung tissue in a dose-dependent manner. Protective effects were less pronounced, if the therapy started later on during an ongoing IAV infection. In addition, simultaneous PDTC treatment also limited IAV-caused infiltration of immune cells as well as local interferon-γ expression in lung tissue. These results imply that PDTC decreases IAV-caused disease in mice significantly. Therefore, the development of drugs like PDTC that interfere with NF-κB signaling may represent a modern focus of anti-IAV therapy.

Antibody-dependent enhancement of coxsackievirus B3 infection of primary CD19+ B lymphocytes.

Coxsackievirus B3 (CVB3) is associated with several different acute and chronic forms of human disease, including myocarditis, aseptic meningitis, and pancreatitis. Moreover, CVB3 also infects immune cells like CD19+ B lymphocytes, but the viral uptake mechanism into these cells is not well understood. Therefore, primary murine and human CD19+ B cells were isolated by magnetic-activated cell separation technology and analyzed for virus receptor expression, antibody-dependent enhancement of viral infection, and different cellular surface proteins, that might be involved in mechanisms of viral uptake. Western blot analysis of these cells revealed no significant expression of the coxsackievirus-adenovirus receptor CAR. But incubation of CVB3 with serum dilutions, which exhibited binding but not neutralizing characteristics, increased viral uptake and replication significantly in a dose-dependent manner. Viral entry was reduced when Fc portions of immunoglobulins were blocked by protein A treatment. Moreover, the classical complement system rather than Fc-gamma-receptor-mediated mechanisms could be involved in viral uptake. Taken together, these data suggest an antibody-dependent enhancement of CVB3 infection of primary murine and human CD19+ B cells.