Recombinant ESAT-6-like proteins provoke protective immune responses against invasive Staphylococcus aureus disease in a murine model.

Staphylococcus aureus is a common pathogen found in the community and in hospitals. Most notably, methicillin-resistant S. aureus is resistant to many antibiotics, which is a growing public health concern. The emergence of drug-resistant strains has prompted the search for alternative treatments, such as immunotherapeutic approaches. To date, most clinical trials of vaccines or of passive immunization against S. aureus have ended in failure. In this study, we investigated two ESAT-6-like proteins secreted by S. aureus, S. aureus EsxA (SaEsxA) and SaEsxB, as possible targets for a vaccine. Mice vaccinated with these purified proteins elicited high titers of anti-SaEsxA and anti-SaEsxB antibodies, but these antibodies could not prevent S. aureus infection. On the other hand, recombinant SaEsxA (rSaEsxA) and rSaEsxB could induce Th1- and Th17-biased immune responses in mice. Mice immunized with rSaEsxA and rSaEsxB had significantly improved survival rates when challenged with S. aureus compared with the controls. These findings indicate that SaEsxA and SaEsxB are two promising Th1 and Th17 candidate antigens which could be developed into multivalent and serotype-independent vaccines against S. aureus infection.

Productive replication of Middle East respiratory syndrome coronavirus in monocyte-derived dendritic cells modulates innate immune response.

The Middle East respiratory syndrome coronavirus (MERS-CoV) closely resembled severe acute respiratory syndrome coronavirus (SARS-CoV) in disease manifestation as rapidly progressive acute pneumonia with multi-organ dysfunction. Using monocyte-derived-dendritic cells (Mo-DCs), we discovered fundamental discrepancies in the outcome of MERS-CoV- and SARS-CoV-infection. First, MERS-CoV productively infected Mo-DCs while SARS-CoV-infection was abortive. Second, MERS-CoV induced significantly higher levels of IFN-γ, IP-10, IL-12, and RANTES expression than SARS-CoV. Third, MERS-CoV-infection induced higher surface expression of MHC class II (HLA-DR) and the co-stimulatory molecule CD86 than SARS-CoV-infection. Overall, our data suggests that the dendritic cell can serve as an important target of viral replication and a vehicle for dissemination. MERS-CoV-infection in DCs results in the production of a rich combination of cytokines and chemokines, and modulates innate immune response differently from that of SARS-CoV-infection. Our findings may help to explain the apparent discrepancy in the pathogenicity between MERS-CoV and SARS-CoV.

Active replication of Middle East respiratory syndrome coronavirus and aberrant induction of inflammatory cytokines and chemokines in human macrophages: implications for pathogenesis.

Middle East respiratory syndrome coronavirus (MERS-CoV) infection caused severe pneumonia and multiorgan dysfunction and had a higher crude fatality rate (around 50% vs. 10%) than SARS coronavirus (SARS-CoV) infection. To understand the pathogenesis, we studied viral replication, cytokine/chemokine response, and antigen presentation in MERS-CoV-infected human monocyte-derived macrophages (MDMs) versus SARS-CoV-infected MDMs. Only MERS-CoV can replicate in MDMs. Both viruses were unable to significantly stimulate the expression of antiviral cytokines (interferon α [IFN-α] and IFN-ß) but induced comparable levels of tumor necrosis factor α and interleukin 6. Notably, MERS-CoV induced significantly higher expression levels of interleukin 12, IFN-γ, and chemokines (IP-10/CXCL-10, MCP-1/CCL-2, MIP-1α/CCL-3, RANTES/CCL-5, and interleukin 8) than SARS-CoV. The expression of major histocompatibility complex class I and costimulatory molecules were significantly higher in MERS-CoV-infected MDMs than in SARS-CoV-infected cells. MERS-CoV replication was validated by immunostaining of infected MDMs and ex vivo lung tissue. We conclusively showed that MERS-CoV can establish a productive infection in human macrophages. The aberrant induction of inflammatory cytokines/chemokines could be important in the disease pathogenesis.

Cross-reactive antibodies in convalescent SARS patients' sera against the emerging novel human coronavirus EMC (2012) by both immunofluorescent and neutralizing antibody tests.

OBJECTIVES: A severe acute respiratory syndrome (SARS)-like disease due to a novel betacoronavirus, human coronavirus EMC (HCoV-EMC), has emerged recently. HCoV-EMC is phylogenetically closely related to Tylonycteris-bat-coronavirus-HKU4 and Pipistrellus-bat-coronavirus-HKU5 in Hong Kong. We conducted a seroprevalence study on archived sera from 94 game-food animal handlers at a wild life market, 28 SARS patients, and 152 healthy blood donors in Southern China to assess the zoonotic potential and evidence for intrusion of HCoV-EMC and related viruses into humans. METHODS: Anti-HCoV-EMC and anti-SARS-CoV antibodies were detected using screening indirect immunofluorescence (IF) and confirmatory neutralizing antibody tests. RESULTS: Two (2.1%) animal handlers had IF antibody titer of ≥ 1:20 against both HCoV-EMC and SARS-CoV with neutralizing antibody titer of <1:10. No blood donor had antibody against either virus. Surprisingly, 17/28 (60.7%) of SARS patients had significant IF antibody titers with 7/28 (25%) having anti-HCoV-EMC neutralizing antibodies at low titers which significantly correlated with that of HCoV-OC43. Bioinformatics analysis demonstrated a significant B-cell epitope overlapping the heptad repeat-2 region of Spike protein. Virulence of SARS-CoV over other betacoronaviruses may boost cross-reactive neutralizing antibodies against other betacoronaviruses. CONCLUSIONS: Convalescent SARS sera may contain cross-reactive antibodies against other betacoronaviruses and confound seroprevalence study for HCoV-EMC.

A functional variation in CD55 increases the severity of 2009 pandemic H1N1 influenza A virus infection.

Infection due to 2009 pandemic H1N1 influenza A virus (A[H1N1]pdm09) is commonly manifested as mild infection but occasionally as severe pneumonia. We hypothesized that host genetic variations may contribute to disease severity. An initially small-scale genome-wide association study guided the selection of CD55 single-nucleotide polymorphisms in 425 Chinese patients with severe (n = 177) or mild (n = 248) disease. Carriers of rs2564978 genotype T/T were significantly associated with severe infection (odds ratio, 1.75; P = .011) under a recessive model, after adjustment for clinical confounders. An allele-specific effect on CD55 expression was revealed and ascribed to a promoter indel variation, which was in complete linkage disequilibrium with rs2564978. The promoter variant with deletion exhibited significantly lower transcriptional activity. We further demonstrated that CD55 can protect respiratory epithelial cells from complement attack. Additionally, A(H1N1)pdm09 infection promoted CD55 expression. In conclusion, CD55 polymorphisms are associated with severe A(H1N1)pdm09 infection. CD55 may exert a substantial impact on the disease severity of A(H1N1)pdm09 infection.

The lower serum immunoglobulin G2 level in severe cases than in mild cases of pandemic H1N1 2009 influenza is associated with cytokine dysregulation.

The majority of patients with pandemic influenza H1N1 2009 had mild illness, but some, including those with no risk factors for severe disease, may succumb to this infection. Besides viral factors such as the D222/225G substitution of the hemagglutinin, host factors such as IgG2 subclass deficiency recently was reported to be associated with severe disease in a cohort of Australian patients besides other known risk factors, including underlying chronic illness, extremes of age, and pregnancy. We conducted a case-control study of 38 Asian patients with respiratory failure due to severe pandemic influenza and compared the results to those for 36 mild cases. None had selective IgG2 deficiency, but the level of IgG2 subclass was significantly lower in the severe cases (3.55 g/liter versus 4.75 g/liter; P = 0.002), whereas the levels of IgG1, IgG3, and IgG4 were not significantly different from those of the mild cases. Previous studies suggested that some IgHG2 and FcγRIIa genotypes were associated with IgG2 deficiency. The allelic frequency of the IgHG2 genotypes in our severe cases was not correlated with their levels of IgG2, while that of FcγRIIa was not significantly different from that of the general Han Chinese population (P = 0.216). Only the overall cytokine/chemokine profile (P = 0.029) and serum globulin level (P = 0.005) were found to be independently associated with the IgG2 level by multivariate analysis. The lower IgG2 level in our severe group might be related to cytokine dysregulation rather than being a significant risk factor for severe pandemic influenza. The importance of this finding for therapeutic intervention will require further studies of larger cohorts of patients.