Peter J. M. Openshaw

IFITM3 restricts the morbidity and mortality associated with influenza

The 2009 H1N1 influenza pandemic showed the speed with which a novel respiratory virus can spread and the ability of a generally mild infection to induce severe morbidity and mortality in a subset of the population. Recent in vitro studies show that the interferon-inducible transmembrane (IFITM) protein family members potently restrict the replication of multiple pathogenic viruses. Both the magnitude and breadth of the IFITM proteins’ in vitro effects suggest that they are critical for intrinsic resistance to such viruses, including influenza viruses. Using a knockout mouse model, we now test this hypothesis directly and find that IFITM3 is essential for defending the host against influenza A virus in vivo. Mice lacking Ifitm3 display fulminant viral pneumonia when challenged with a normally low-pathogenicity influenza virus, mirroring the destruction inflicted by the highly pathogenic 1918 ‘Spanish’ influenza. Similar increased viral replication is seen in vitro, with protection rescued by the re-introduction of Ifitm3. To test the role of IFITM3 in human influenza virus infection, we assessed the IFITM3 alleles of individuals hospitalized with seasonal or pandemic influenza H1N1/09 viruses. We find that a statistically significant number of hospitalized subjects show enrichment for a minor IFITM3 allele (SNP rs12252-C) that alters a splice acceptor site, and functional assays show the minor CC genotype IFITM3 has reduced influenza virus restriction in vitro. Together these data reveal that the action of a single intrinsic immune effector, IFITM3, profoundly alters the course of influenza virus infection in mouse and humans.

Age at First Viral Infection Determines the Pattern of T Cell–mediated Disease during Reinfection in Adulthood

Infants experiencing severe respiratory syncytial virus (RSV) bronchiolitis have an increased frequency of wheeze and asthma in later childhood. Since most severe RSV infections occur between the 8th and 24th postnatal week, we examined whether age at first infection determines the balance of cytokine production and lung pathology during subsequent rechallenge. Primary RSV infection in newborn mice followed the same viral kinetics as in adults but was associated with reduced and delayed IFN-γ responses. To study rechallenge, mice were infected at 1 day or 1, 4, or 8 weeks of age and reinfected at 12 weeks. Neonatal priming produced more severe weight loss and increased inflammatory cell recruitment (including T helper 2 cells and eosinophils) during reinfection, whereas delayed priming led to enhanced interferon γ production and less severe disease during reinfection. These results show the crucial importance of age at first infection in determining the outcome of reinfection and suggest that the environment of the neonatal lung is a major determinant of cytokine production and disease patterns in later life. Thus, simply delaying RSV infection beyond infancy might reduce subsequent respiratory morbidity in later childhood.

Immune Responses and Disease Enhancement during Respiratory Syncytial Virus Infection

SUMMARY Respiratory syncytial virus (RSV) is one of the commonest and most troublesome viruses of infancy. It causes most cases of bronchiolitis, which is associated with wheezing in later childhood. In primary infection, the peak of disease typically coincides with the development of specific T- and B-cell responses, which seem, in large part, to be responsible for disease. Animal models clearly show that a range of immune responses can enhance disease severity, particularly after vaccination with formalin-inactivated RSV. Prior immune sensitization leads to exuberant chemokine production, an excessive cellular influx, and an overabundance of cytokines during RSV challenge. Under different circumstances, specific mediators and T-cell subsets and antibody-antigen immune complex deposition are incriminated as major factors in disease. Animal models of immune enhancement permit a deep understanding of the role of specific immune responses in RSV disease, assist in vaccine design, and indicate which immunomodulatory therapy might be beneficial to children with bronchiolitis.

Flow cytometric measurement of intracellular cytokines.

The identification of distinct T helper lymphocyte subsets (Th1/2) with polarised cytokine production has opened up new fields in immunobiology. Of the several alternative methods of monitoring cytokine production, flow cytometric analysis of intracellular staining has distinct advantages and pitfalls. It allows high throughput of samples and multiparameter characterisation of cytokine production on a single cell basis without the need for prolonged in vitro culture and cloning. However, these methods may cause important changes in cell surface phenotype which can make interpretation difficult.

Inhibition of tumor necrosis factor reduces the severity of virus-specific lung immunopathology.

TNF antagonists are effective treatments for rheumatoid arthritis and Crohn′s disease, and have been tried with variable success in other diseases caused by immune damage. To test the hypothesis that viral lung diseases caused by respiratory syncytial virus or influenza virus are partly due to overproduction of TNF, we used anti‐TNF antibody to treat mice with lung disease caused by these viruses. TNF depletion reduced pulmonary recruitment of inflammatory cells, cytokine production by T cells and the severity of illness without preventing virus clearance. These broad beneficial effects suggest that TNF antagonists might be tested as treatments of human viral lung diseases.

Risk factors for hospitalisation and poor outcome with pandemic A/H1N1 influenza: United Kingdom first wave (May–September 2009)

Background During the first wave of pandemic H1N1 influenza in 2009, most cases outside North America occurred in the UK. The clinical characteristics of UK patients hospitalised with pandemic H1N1 infection and risk factors for severe outcome are described. Methods A case note-based investigation was performed of patients admitted with confirmed pandemic H1N1 infection. Results From 27 April to 30 September 2009, 631 cases from 55 hospitals were investigated. 13% were admitted to a high dependency or intensive care unit and 5% died; 36% were aged <16 years and 5% were aged ≥65 years. Non-white and pregnant patients were over-represented. 45% of patients had at least one underlying condition, mainly asthma, and 13% received antiviral drugs before admission. Of 349 with documented chest x-rays on admission, 29% had evidence of pneumonia, but bacterial co-infection was uncommon. Multivariate analyses showed that physician-recorded obesity on admission and pulmonary conditions other than asthma or chronic obstructive pulmonary disease (COPD) were associated with a severe outcome, as were radiologically-confirmed pneumonia and a raised C-reactive protein (CRP) level (≥100 mg/l). 59% of all in-hospital deaths occurred in previously healthy people. Conclusions Pandemic H1N1 infection causes disease requiring hospitalisation of previously fit individuals as well as those with underlying conditions. An abnormal chest x-ray or a raised CRP level, especially in patients who are recorded as obese or who have pulmonary conditions other than asthma or COPD, indicate a potentially serious outcome. These findings support the use of pandemic vaccine in pregnant women, children <5 years of age and those with chronic lung disease.

Th1 and Th2 cytokine induction in pulmonary T cells during infection with respiratory syncytial virus

Helper T (Th) cells can be classified functionally into two main types. Broadly, Th1 cells play a major role in eliminating viral pathogens, while Th2 cells mediate anti-parasite immunity and allergic responses. These functions are thought to depend on characteristic and distinct patterns of cytokine production. Infection with human respiratory syncytial virus, an important common cold virus, causes transient lymphocytic bronchiolitis in mice. Activated T cells are partly responsible for this disease, but also eliminate the virus. To show whether polarized cytokine production occurs in individual cells during viral bronchiolitis, we sampled murine bronchoalveolar lavage and mediastinal lymph node cells before and after infection. RT-PCR of cellular mRNA and flow cytometric analysis of intracellular cytokine production showed a rapid IFN-gamma response at both sites, which persisted for more than 3 weeks in the lung. Most IFN-gamma-producing cells were CD8+. Some early CD4+ IFN-gamma-producing cells also made IL-10. Only low levels of IL-2, IL-4 and IL-5 mRNA or protein expression were detected at any time at either site. No cytokines were detected in B cell populations at either site. These novel techniques show the true complexity of cytokine production patterns on a cell-by-cell basis, allowing T cells to be reclassified according to function.

Intracellular IFN-gamma expression in natural killer cells precedes lung CD8+ T cell recruitment during respiratory syncytial virus infection.

Natural killer (NK) cells are recruited locally during the initial phases of virus infection and produce cytokines which may affect the subsequent emergence of specific T cells. In this study, cellular responses to primary respiratory syncytial virus (RSV) infection and after vaccination with individual viral proteins were investigated in BALB/c mice using the new NK cell antibody, DX5. Purified DX5+ cells caused lysis of YAC-1 cell targets. DX5+ cells did not express CD8, CD45R or MHC class II antigens. A small proportion of DX5+ cells co-expressed CD4 (10.3%) and CD3 (10.6%). Of the DX5+/CD4+ cells, the majority expressed the alpha/beta T cell receptor and less than 1% expressed the gamma/delta T cell receptor. During infection with RSV, lung DX5+/CD3- NK cells peaked on day 4 of primary infection and were the most numerous subset producing IFN-gamma, as determined by intracellular staining, at this time-point. Less than 1% of the DX5+ cells secreting IFN-gamma were CD4+. In the lungs of mice vaccinated with recombinant vaccinia virus expressing individual RSV proteins, increased NK cell cytotoxicity and IFN-gamma production correlated with increased numbers of CD8+ T cells. Mice with few NK cells subsequently had low CD8+ T cells and developed lung eosinophilia. IFN-gamma-producing NK cells therefore form a substantial component of the early cellular response to virus infection with important potential influences on the subsequent development of specific immunity.

CD4+ T cells clear virus but augment disease in mice infected with respiratory syncytial virus. Comparison with the effects of CD8+ T cells

Respiratory syncytial (RS) virus‐specific T cell lines were derived from the spleens of BALB/c mice primed by intranasal infection with RS virus. The lines were expanded by repealed antigenic stimulation in vitro, and separated into CD4+ and CD8+ T cell‐enriched fractions by immunomagnetic adhesion. The effects of passive transfer of these fractions into RS virus infected mice were observed. The most severe immunopathological changes were seen in mice receiving CD4+ cells. Transfer of CD4+, CD8+ or both cell fractions caused RS virus‐infected mice to become ill and lose weight. Both cell lines caused an increase in the severity of lung pathology (as monitored by bronchoalveolar lavage) with the appearance or lung haemorrhage and polymorphonuclear cell efflux. In addition, recipients of CD4+ cells developed striking pulmonary eosinophilia. In CD4+ cell recipients. 5×105 cells were sufficient to decrease lung virus titr, whereas 2×106 CD8+ cells were needed to produce a similar effect. The unseparated T cell line and the CD4+ cell fraction secreted significant amounts of IL‐3, IL‐4 and IL‐5 (P < 0·001). High levels of IL‐2 were produced only by the unseparated T cell line. The CD8+ cell fraction secreted IL‐3 only. The results show that, cell‐for‐cell CD4+ cells are more anti‐viral and more immunopathogenic than CD8+ cells in RS virus infected mice. Such effects may have contributed to the augmented disease seen in some infants vaccinated against RS virus.

A potential molecular mechanism for hypersensitivity caused by formalin-inactivated vaccines

Heat, oxidation and exposure to aldehydes create reactive carbonyl groups on proteins, targeting antigens to scavenger receptors. Formaldehyde is widely used in making vaccines, but has been associated with atypical enhanced disease during subsequent infection with paramyxoviruses. We show that carbonyl groups on formaldehyde-treated vaccine antigens boost T helper type 2 (TH2) responses and enhance respiratory syncytial virus (RSV) disease in mice, an effect partially reversible by chemical reduction of carbonyl groups.