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Enhanced virulence of influenza A viruses with the haemagglutinin of the 1918 pandemic virus


The ‘Spanish’ influenza pandemic of 1918–19 was the most devastating outbreak of infectious disease in recorded history. At least 20 million people1 died from their illness, which was characterized by an unusually severe and rapid clinical course. The complete sequencing of several genes of the 1918 influenza virus has made it possible to study the functions of the proteins encoded by these genes in viruses generated by reverse genetics, a technique that permits the generation of infectious viruses entirely from cloned complementary DNA. Thus, to identify properties of the 1918 pandemic influenza A strain that might be related to its extraordinary virulence, viruses were produced containing the viral haemagglutinin2 (HA) and neuraminidase3 (NA) genes of the 1918 strain. The HA of this strain supports the pathogenicity of a mouse-adapted virus in this animal4,5. Here we demonstrate that the HA of the 1918 virus confers enhanced pathogenicity in mice to recent human viruses that are otherwise non-pathogenic in this host. Moreover, these highly virulent recombinant viruses expressing the 1918 viral HA could infect the entire lung and induce high levels of macrophage-derived chemokines and cytokines, which resulted in infiltration of inflammatory cells and severe haemorrhage, hallmarks of the illness produced during the original pandemic6.

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We thank D. Dick, A. Grolla, M. Garbutt and S. Jones for assistance with BL4 procedures, M. McGregor and K. Wells for technical assistance, J. Gilbert for editing the manuscript, and Y. Kawaoka for illustrations. This work was supported by a grant-in-aid from the Japanese Ministry of Education, Culture, Sports, Science and Technology, CREST (Japan Science and Technology Corporation), NIAID Public Health Service research grants and Health Canada.

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Correspondence to Yoshihiro Kawaoka.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Figure 1

Global lung lesions caused by M88/Hsp or M88 virus. The figure shows hematoxylin-eosin staining and antigen distribution in whole lung sections on day 6 p.i. from mice infected with M88/Hsp or M88. (PDF 516 kb)

Supplementary Figure 2

Pathologic lesions in mice infected with WSN/HspNsp or WSN. Hematoxylin-eosin staining and detection of antigen distribution is shown on day 6 p.i. (PDF 1382 kb)

Supplementary Figure 3

Cytokine expression in the lungs of mice infected with M88/Hsp or M88 or mock infected (PBS). This figure shows the analysis of levels of 11 cytokines on days 1, 3, 5 and 6 p.i. (PDF 13 kb)

Supplementary Table 1

Shown are titres of virus recovered from the lungs of mice infected with WSN/HspNsp or WSN on both days 3 and 6 p.i. to indicate that, even though pathologic lesions observed with WSN/HspNsp are much more severe than with WSN (Supplementary Fig. 2), these viruses replicate to similar titres at both timepoints. (DOC 22 kb)

Supplementary Table 2

The table contains the data from Fig. 4 in a nongraphical form to allow direct comparison of the neutralization titres of each serum serum sample against WSN/HspNsp and a recent human H1N1 virus (A/Kawasaki/233/01). (DOC 39 kb)

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Further reading

Figure 1: Pathological examination of lungs infected with the M88/Hsp or M88 viruses.
Figure 3: Cytokine expression in lungs of mice infected with M88/Hsp and M88 or mock infected (PBS).
Figure 2: Competitive binding assay for haemagglutinin receptor specificity.
Figure 4: Neutralization activities in human sera against a virus possessing Hsp and Nsp.


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