Immunoglobulin A responses to Puumala hantavirus

Hemorrhagic Fever with Renal Syndrome: Literature Review, Epidemiology, Clinical Picture and Pathogenesis

Hantaviruses can cause two types of infections in humans: hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome. The old world hantaviruses, primarily Hantaan virus (HTNV), responsible for causing HFRS occurs endemically in Asia and Europe. Apodernus agraricus, a striped field mouse, is being considered as main host reservoir for HTNV. Infection in humans is typically accidental and occurs when virus-containing rodent excretions such as urine, feces, or saliva are aerosolized. The major clinical manifestations includes increased vascular permeability causing vascular leakage, acute kidney injury and coagulation abnormalities. The case fatality rate of HFRS varies around 5.0 - 10.0% depending on the causative viral agent. The direct effects of viral infection on endothelial cells, as well as the immunological response to the viral infection, have been suggested to play a key role in the pathogenesis of HFRS. This article summarizes the current knowledge of HFRS epidemiology in Korea and around the globe, etiology, host transmission, clinical presentation, pathogenesis, diagnostic techniques, treatment, and prevention.

Generation of plasma cells and CD27-IgD- B cells during hantavirus infection is associated with distinct pathological findings

OBJECTIVE

Human hantavirus infections can cause haemorrhagic fever with renal syndrome (HFRS). The pathogenic mechanisms are not fully understood, nor if they affect the humoral immune system. The objective of this study was to investigate humoral immune responses to hantavirus infection and to correlate them to the typical features of HFRS: thrombocytopenia and transient kidney dysfunction.

METHODS

We performed a comprehensive characterisation of longitudinal antiviral B-cell responses of 26 hantavirus patients and combined this with paired clinical data. In addition, we measured extracellular adenosine triphosphate (ATP) and its breakdown products in circulation and performed in vitro stimulations to address its effect on B cells.

RESULTS

We found that thrombocytopenia was correlated to an elevated frequency of plasmablasts in circulation. In contrast, kidney dysfunction was indicative of an accumulation of CD27-IgD- B cells and CD27-/low plasmablasts. Finally, we provide evidence that high levels of extracellular ATP and matrix metalloproteinase 8 can contribute to shedding of CD27 during human hantavirus infection.

CONCLUSION

Our findings demonstrate that thrombocytopenia and kidney dysfunction associate with distinctly different effects on the humoral immune system. Moreover, hantavirus-infected individuals have significantly elevated levels of extracellular ATP in circulation.

The Immune Correlates of Orthohantavirus Vaccine

Zoonotic transmission of orthohantaviruses from rodent reservoirs to humans has been the cause of severe fatalities. Human infections are reported worldwide, but vaccines have been approved only in China and Korea. Orthohantavirus vaccine development has been pursued with no sense of urgency due to the relative paucity of cases in countries outside China and Korea. However, the orthohantaviruses continuously evolve in hosts and thus the current vaccine may not work as well against some variants. Therefore, a more effective vaccine should be prepared against the orthohantaviruses. In this review, we discuss the issues caused by the orthohantavirus vaccine. Given the pros and cons of the orthohantavirus vaccine, we suggest strategies for the development of better vaccines in terms of pandemic preparedness.

Hemorrhagic Fever with Renal Syndrome: Pathogenesis and Clinical Picture

Hantaan virus (HTNV) causes hemorrhagic fever with renal syndrome (HFRS), which is a zoonosis endemic in eastern Asia, especially in China. The reservoir host of HTNV is field mouse (Apodemus agraricus). The main manifestation of HFRS, including acute kidney injury, increases vascular permeability, and coagulation abnormalities. In this paper, we review the current knowledge of the pathogenesis of HFRS including virus factor, immunity factor and host genetic factors. Furthermore, the treatment and prevention will be discussed.

Viral load and humoral immune response in association with disease severity in Puumala hantavirus-infected patients--implications for treatment

Hantaviruses are the causative agents of haemorrhagic fever with renal syndrome (HFRS) in Eurasia and of hantavirus cardiopulmonary syndrome (HCPS) in the Americas. The case fatality rate varies between different hantaviruses and can be up to 40%. At present, there is no specific treatment available. The hantavirus pathogenesis is not well understood, but most likely, both virus-mediated and host-mediated mechanisms are involved. The aim of the present study was to investigate the association among Puumala hantavirus (PUUV) viral RNA load, humoral immune response and disease severity in patients with HFRS. We performed a study of 105 PUUV-infected patients that were followed during the acute phase of disease and for up to 1–3 months later. Fifteen of the 105 patients (14%) were classified as having moderate/severe disease. A low PUUV-specific IgG response (p <0.05) and also a higher white blood cell count (p <0.001) were significantly associated with more severe disease. The PUUV RNA was detected in a majority of patient plasma samples up to 9 days after disease onset; however, PUUV RNA load or longevity of viraemia were not significantly associated with disease severity. We conclude that a low specific IgG response was associated with disease severity in patients with HFRS, whereas PUUV RNA load did not seem to affect the severity of HFRS. Our results raise the possibility of passive immunotherapy as a useful treatment for hantavirus-infected patients.

Specific humoral reaction of hemorrhagic fever with renal syndrome (HFRS) patients in China to recombinant nucleocapsid proteins from European hantaviruses

Hemorrhagic fever with renal syndrome (HFRS) is endemic in East Asia and Europe. This study was initiated to investigate the reactivity of antibodies in sera of Chinese HFRS patients with the recombinant nucleocapsid proteins (rNPs) of Hantaan virus (HTNV), Dobrava-Belgrade virus (DOBV), and Puumala virus (PUUV), which are the prevalent hantavirus strains in Europe. Forty-eight pairs of acute and convalescent sera were collected from HFRS patients in Hubei, China (1985-2002) and tested by indirect IgG, IgA, and IgM enzyme-linked immunosorbent assays with six rNPs of European hantaviruses as coated antigens, respectively. The results showed that the sensitivity of rNPs against IgG was HTNV-rNP > DOBV-rNP > PUUV-rNP, while the sensitivity against IgA was DOBV-rNP > HTNV-rNP > PUUV-rNP. Quantitative analysis revealed both acute and convalescent sera from HFRS patients predominantly exhibit high levels of IgA. Although PUUV-rNPs showed very weak reactivity to the three kinds of immunoglobulins in all samples, three pairs of sera unexpectedly cross-reacted strongly to all three PUUV-rNP subtypes. We first observe that HFRS patients' sera from Hubei Province show new prevalent characteristics of cross-reacting with PUUV-rNPs and continued high level of IgA in convalescent phase, as well as in China.

Development of novel immunoglobulin G (IgG), IgA, and IgM enzyme immunoassays based on recombinant Puumala and Dobrava hantavirus nucleocapsid proteins

Human infections with Asian and European hantaviruses can result in hemorrhagic fever with renal syndromes of differing severities characterized by renal dysfunction and sometimes by pulmonary symptoms. For the serological detection of human infections by hantaviruses relevant for Europe, we developed monoclonal antibody capture immunoglobulin G (IgG) and IgA enzyme-linked immunosorbent assays (ELISAs) based on yeast-expressed nucleocapsid proteins of Puumala and Dobrava hantaviruses. Moreover, for diagnosis of acute infections, mu-capture IgM ELISAs were established with nucleocapsid proteins expressed in Drosophila melanogaster Schneider S2 cells. The cutoff values of the ELISAs were determined by investigation of up to 500 human anti-hantavirus-negative serum samples. The specificities of the Puumala and Dobrava virus-specific IgM, IgA, and IgG ELISAs were found to be 100%. The sensitivities of these ELISAs were determined to be 100% with panels of characterized anti-Puumala or anti-Dobrava virus-positive human serum samples. In most cases, Puumala and Dobrava virus infections could be differentiated by ELISA reactivity alone, i.e., endpoint titration with homologous and heterologous antigens.

Presence of HIV-1 neutralizing IgA antibodies in primary HIV-1 infected patients

The initial control of viral replication during primary HIV-1 infection is dominated by CD8+ T-cell mediated responses. Neutralizing IgG to autologous virus is first detected in serum weeks after this response when the viraemia has already declined. However, the mucosal and systemic HIV-1 neutralizing IgA response during primary HIV-1 infection in patients treated with HAART has not been studied previously. The presence of HIV-1 neutralizing IgA antibodies in serum (n=10 patients) and semen (n=6 patients) samples was tested against a laboratory adapted HIV-1 isolate and against primary HIV-1 isolates, representing different clades and phenotypes. The patients received HAART during the study period and were followed from primary HIV-1 infection and up to 72 weeks. Overall, HIV-1 neutralizing IgA activity could be demonstrated in serum from 5 of 10 primary HIV-1 infected patients at inclusion, although the response was restricted to only 1 of the 4 tested isolates. In semen samples, HIV-1 neutralizing IgA activity was seen in 2 of 5 patients against at least 1 of the HIV-1 isolates. In conclusion, a restricted but early neutralizing IgA response can be detected in serum and semen in primary infected patients treated with HAART.

Immune responses to Puumala virus infection and the pathogenesis of nephropathia epidemica

Puumala virus, causative agent of a mild form of hemorrhagic fever with renal syndrome, also known as nephropathia epidemica, induces long-lasting humoral and cellular immunity in patients. The virus itself is not cytopathic, and the immune responses to the virus may be involved in teh pathogenesis of the disease.

Serum immunoglobulin A (IgA)-mediated immunity in human immunodeficiency virus type 2 (HIV-2) infection

In the present study, we sought to define the importance of serum IgA (sIgA)-mediated immunity in HIV-2 infection. Serum samples from a total of 29 HIV-2-infected patients from Guinea-Bissau (n = 20) and Portugal (n = 9) were studied. Samples from seronegative individuals were used as controls. Antibody reactivity to native and recombinant envelope glycoproteins as well as peptides representing various regions of the envelope glycoproteins was investigated. Furthermore, the capacity of purified IgA to neutralize the HIV-2(SBL6669) strain was tested. All serum samples showed IgA reactivity against whole HIV-2 antigen. Twenty-eight out of 29 IgA samples (96%) reacted with native HIV-2 gp125, 26/29 (90%) with recombinant gp105, and 29/29 (100%) with recombinant gp36. When using peptides, the most prominent IgA reactivity was seen against the peptide representing aa 644-658 of the transmembranous protein gp36, to which 72% of the sera reacted. Purified sIgA antibodies showed neutralizing effects against HIV-2(SBL6669) in 17/29 cases (59%). This work describes the HIV-2-specific sIgA antigenic response. Moreover, our findings show, for the first time, that sIgA may play a role in the in vitro neutralization of HIV-2.

Hantavirus immunology

Two clinical syndromes are associated with hantavirus infection in humans: hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). Autopsy findings typically reveal a common feature of increased permeability in microvascular beds, suggesting vascular endothelium is a prime target for virus infection. Endothelial cells are susceptible to hantavirus infection; however, virus does not cause cytopathic effects, to explain increased endothelium permeability. Therefore, immune mechanisms were suggested to play a crucial role in hantavirus pathogenesis. In this review, we summarize data on hantavirus-induced immune disturbances and discuss their implication in capillary leakage caused by hantavirus infection.

T-helper and humoral responses to Puumala hantavirus nucleocapsid protein: identification of T-helper epitopes in a mouse model

Puumala hantavirus (PUUV) is a rodent-borne agent causing nephropathia epidemica in humans, a milder form of haemorrhagic fever with renal syndrome occurring in Fennoscandia, central Europe and western Russia. In this study we characterized the immunogenicity of an E. coli-expressed nucleocapsid (N) protein of PUUV (strain Kazan-E6) in inbred mice (BALB/c, CBA and C57/BL6). The recombinant N (rN) protein raised PUUV-specific antibodies in all three tested murine haplotypes, and all IgG subclasses were detected. Epitope mapping using peptides spanning the N protein revealed that the B-cell recognition sites were mainly located at the amino-terminal part of the protein. Proliferative T-helper (Th) lymphocyte responses were detected in all haplotypes after a single immunization with rN. Several Th-recognition sites, spanning amino acids 6-27, 96-117, 211-232 and 256-277, were identified using overlapping peptides. Peptides representing the identified sites could also prime Th-lymphocytes to proliferate in response to recall with rN protein, thereby confirming the authenticity of the identified sites. The rN-primed Th-lymphocytes produced predominantly interleukin (IL)-2 and gamma interferon, together with lower levels of IL-4 and IL-6, indicating a mixed Th1/Th2 response.