Interferon type 1 responses in primary and secondary infections

The mammalian host responds to a microbial infection with a rapid innate immune reaction that is dominated by type I interferon (IFN-I) release. Most cells of vertebrates can respond to microbial attack with IFN-I production, but the cell type responsible for most of the systemic IFN-I release is thought to be plasmacytoid dendritic cells (pDCs). Besides its anti-microbial and especially anti-viral properties IFN-I also exerts a regulatory role on many facets of the sequential adaptive immune response. One of these is being the recently described partial, systemic activation of the vast majority of B and T lymphocytes in mice, irrespective of antigen reactivity. The biological significance of this partial activation of lymphocytes is at present speculative. Secondary infections occurring within a short time span of a primary infection fail to elicit a similar lymphocyte activation response due to a refractory period in systemic IFN-I production. This period of exhaustion in IFN-I responses is associated with an increased susceptibility of the host to secondary infections. The latter correlates with well-established clinical observations of heightened susceptibility of patients to secondary microbial infections after viral episodes

MHC Class II–Alpha Chain Knockout Mice Support Increased Viral Replication That Is Independent of Their Lack of MHC Class II Cell Surface Expression and Associated Immune Function Deficiencies

MHCII molecules are heterodimeric cell surface proteins composed of an α and β chain. These molecules are almost exclusively expressed on thymic epithelium and antigen presenting cells (APCs) and play a central role in the development and function of CD4 T cells. Various MHC-II knockout mice have been generated including MHC-IIAα(-/-) (I-Aα(-/-)), MHC-IIAβ(-/-) (I-β(-/-)) and the double knockout (I-Aαxβ(-/-)). Here we report a very striking observation, namely that alphaviruses including the avirulent strain of Semliki Forest virus (aSFV), which causes asymptomatic infection in wild-type C57BL6/J (B6) mice, causes a very acute and lethal infection in I-Aα(-/-), but not in I-β(-/-) or I-Aαxβ(-/-), mice. This susceptibility to aSFV is associated with high virus titres in muscle, spleen, liver, and brain compared to B6 mice. In addition, I-Aα(-/-) mice show intact IFN-I responses in terms of IFN-I serum levels and IFN-I receptor expression and function. Radiation bone marrow chimeras of B6 mice reconstituted with I-Aα(-/-) bone marrow expressed B6 phenotype, whereas radiation chimeras of I-Aα(-/-) mice reconstituted with B6 bone marrow expressed the phenotype of high viral susceptibility. Virus replication experiments both in vivo and in vitro showed enhanced virus growth in tissues and cell cultures derived form I-Aα(-/-) compared to B6 mice. This enhanced virus replication is evident for other alpha-, flavi- and poxviruses and may be of great benefit to producers of viral vaccines. In conclusion, I-Aα(-/-) mice exhibit a striking susceptibility to virus infections independent of their defective MHC-II expression. Detailed genetic analysis will be carried out to characterise the underlining genetic defects responsible for the observed phenomenon.This work was supported by institutional research support to Prof Mullbacher laboratory at the John Curtin School of Medical Research. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Gamma-irradiated influenza A virus provides adjuvant activity to a co-administered poorly immunogenic SFV vaccine in mice

Many currently available inactivated vaccines require "adjuvants" to maximize the protective immune responses generated against the antigens of interest. Recent studies in mice with gamma-irradiated influenza A virus (γ-FLU) have shown its superior efficacy compared to other forms of inactivated FLU vaccines and its ability to induce both potent interferon type-I (IFN-I) responses and the IFN-I-associated partial lymphocyte activation. Commonly, IFN-I responses induced by adjuvants, combined in vaccine preparations, have been shown to effectively enhance the immunogenicity of the antigens of interest. Therefore, we investigated the potential adjuvant activity of γ-FLU and the possible effect on antibody responses against co-administrated antigens, using gamma-irradiated Semliki Forest virus (γ-SFV) as the experimental vaccine in mice. Our data show that co-vaccination with γ-FLU and γ-SFV resulted in enhanced SFV-specific antibody responses in terms of increased titers by sixfold and greater neutralization efficacy, when compared to vaccination with γ-SFV alone. This study provides promising evidence related to the possible use of γ-FLU as an adjuvant to poorly immunogenic vaccines without compromising the vaccine efficacy of γ-FLU

Intranasal Flu Vaccine Protective against Seasonal and H5N1 Avian Influenza Infections

Background Influenza A (flu) virus causes significant morbidity and mortality worldwide, and current vaccines require annual updating to protect against the rapidly arising antigenic variations due to antigenic shift and drift. In fact, current subunit or split flu vaccines rely exclusively on antibody responses for protection and do not induce cytotoxic T (Tc) cell responses, which are broadly cross-reactive between virus strains. We have previously reported that γ-ray inactivated flu virus can induce cross-reactive Tc cell responses. Methodology/Principal Finding Here, we report that intranasal administration of purified γ-ray inactivated human influenza A virus preparations (γ-Flu) effectively induces heterotypic and cross-protective immunity. A single intranasal administration of γ-A/PR8[H1N1] protects mice against lethal H5N1 and other heterotypic infections. Conclusions/Significance Intranasal γ-Flu represents a unique approach for a cross-protective vaccine against both seasonal as well as possible future pandemic influenza A virus infections.Mohammed Alsharifi, Yoichi Furuya, Timothy R. Bowden, Mario Lobigs, Aulikki Koskinen, Matthias Regner, Lee Trinidad, David B. Boyle and Arno Müllbache

Gamma-Irradiated Influenza Virus Uniquely Induces IFN-I Mediated Lymphocyte Activation Independent of the TLR7/MyD88 Pathway

Background: We have shown previously in mice, that infection with live viruses, including influenza/A and Semliki Forest virus (SFV), induces systemic partial activation of lymphocytes, characterized by cell surface expression of CD69 and CD86, but not CD25. This partial lymphocytes activation is mediated by type-I interferons (IFN-I). Importantly, we have shown that c-irradiated SFV does not induce IFN-I and the associated lymphocyte activation. Principal Findings: Here we report that, in contrast to SFV, c-irradiated influenza A virus elicits partial lymphocyte activation in vivo. Furthermore, we show that when using influenza viruses inactivated by a variety of methods (UV, ionising radiation and formalin treatment), as well as commercially available influenza vaccines, only c-irradiated influenza virus is able to trigger IFN-I-dependent partial lymphocyte activation in the absence of the TLR7/MyD88 signalling pathways. Conclusions: Our data suggest an important mechanism for the recognition of c-irradiated influenza vaccine by cytosolic receptors, which correspond with the ability of c-irradiated influenza virus to induce cross-reactive and cross-protective cytotoxic T cell responses.Yoichi Furuya, Jennifer Chan, En-Chi Wan, Aulikki Koskinen, Kerrilyn R. Diener, John D. Hayball, Matthias Regner, Arno Müllbacher, Mohammed Alsharif

Atypical chemokine receptor 4 shapes activated B cell fate

Activated B cells can initially differentiate into three functionally distinct fates-early plasmablasts (PBs), germinal center (GC) B cells, or early memory B cells-by mechanisms that remain poorly understood. Here, we identify atypical chemokine receptor 4 (ACKR4), a decoy receptor that binds and degrades CCR7 ligands CCL19/CCL21, as a regulator of early activated B cell differentiation. By restricting initial access to splenic interfollicular zones (IFZs), ACKR4 limits the early proliferation of activated B cells, reducing the numbers available for subsequent differentiation. Consequently, ACKR4 deficiency enhanced early PB and GC B cell responses in a CCL19/CCL21-dependent and B cell-intrinsic manner. Conversely, aberrant localization of ACKR4-deficient activated B cells to the IFZ was associated with their preferential commitment to the early PB linage. Our results reveal a regulatory mechanism of B cell trafficking via an atypical chemokine receptor that shapes activated B cell fate

An empirical approach towards the efficient and optimal production of influenza-neutralizing ovine polyclonal antibodies demonstrates that the novel adjuvant CoVaccine HT(TM) is functionally superior to Freund's adjuvant

Passive immunotherapies utilising polyclonal antibodies could have a valuable role in preventing and treating infectious diseases such as influenza, particularly in pandemic situations but also in immunocompromised populations such as the elderly, the chronically immunosuppressed, pregnant women, infants and those with chronic diseases. The aim of this study was to optimise current methods used to generate ovine polyclonal antibodies. Polyclonal antibodies to baculovirus-expressed recombinant influenza haemagglutinin from A/Puerto Rico/8/1934 H1N1 (PR8) were elicited in sheep using various immunisation regimens designed to investigate the priming immunisation route, adjuvant formulation, sheep age, and antigen dose, and to empirically ascertain which combination maximised antibody output. The novel adjuvant CoVaccine HT™ was compared to Freund’s adjuvant which is currently the adjuvant of choice for commercial production of ovine polyclonal Fab therapies. CoVaccine HT™ induced significantly higher titres of functional ovine anti-haemagglutinin IgG than Freund’s adjuvant but with fewer side effects, including reduced site reactions. Polyclonal hyperimmune sheep sera effectively neutralised influenza virus in vitro and, when given before or after influenza virus challenge, prevented the death of infected mice. Neither the age of the sheep nor the route of antigen administration appeared to influence antibody titre. Moreover, reducing the administrated dose of haemagglutinin antigen minimally affected antibody titre. Together, these results suggest a cost effective way of producing high and sustained yields of functional ovine polyclonal antibodies specifically for the prevention and treatment of globally significant diseases.Natalie E. Stevens, Cara K. Fraser, Mohammed Alsharifi, Michael P. Brown, Kerrilyn R. Diener, John D. Haybal

Atypical chemokine receptor 4 shapes activated B cell fate

Activated B cells can initially differentiate into three functionally distinct fates-early plasmablasts (PBs), germinal center (GC) B cells, or early memory B cells-by mechanisms that remain poorly understood. Here, we identify atypical chemokine receptor 4 (ACKR4), a decoy receptor that binds and degrades CCR7 ligands CCL19/CCL21, as a regulator of early activated B cell differentiation. By restricting initial access to splenic interfollicular zones (IFZs), ACKR4 limits the early proliferation of activated B cells, reducing the numbers available for subsequent differentiation. Consequently, ACKR4 deficiency enhanced early PB and GC B cell responses in a CCL19/CCL21-dependent and B cell-intrinsic manner. Conversely, aberrant localization of ACKR4-deficient activated B cells to the IFZ was associated with their preferential commitment to the early PB linage. Our results reveal a regulatory mechanism of B cell trafficking via an atypical chemokine receptor that shapes activated B cell fate.This work was supported in part by a grant from the Australian National Health and Medical Research Council (APP1105312) to S.R. McColl, J.G. Cyster, and I. Comerford, J.G. Cyster is an investigator of the Howard Hughes Medical Institute. E.E. Kara is supported by an Australian postgraduate award, a Norman and Patricia Polglase scholarship, and a National Health and Medical Research Council C.J. Martin Overseas Biomedical fellowship

Complex patterns of human antisera reactivity to novel 2009 H1N1 and historical H1N1 influenza strains

Background: During the 2009 influenza pandemic, individuals over the age of 60 had the lowest incidence of infection with approximately 25% of these people having pre-existing, cross-reactive antibodies to novel 2009 H1N1 influenza isolates. It was proposed that older people had pre-existing antibodies induced by previous 1918-like virus infection(s) that cross-reacted to novel H1N1 strains. Methodology/Principal Findings: Using antisera collected from a cohort of individuals collected before the second wave of novel H1N1 infections, only a minority of individuals with 1918 influenza specific antibodies also demonstrated hemagglutination-inhibition activity against the novel H1N1 influenza. In this study, we examined human antisera collected from individuals that ranged between the ages of 1 month and 90 years to determine the profile of seropositive influenza immunity to viruses representing H1N1 antigenic eras over the past 100 years. Even though HAI titers to novel 2009 H1N1 and the 1918 H1N1 influenza viruses were positively associated, the association was far from perfect, particularly for the older and younger age groups. Conclusions/Significance: Therefore, there may be a complex set of immune responses that are retained in people infected with seasonal H1N1 that can contribute to the reduced rates of H1N1 influenza infection in older populations. © 2012 Carter et al