Eurasian Avian-like M1 Plays More Important Role than M2 in Pathogenicity of 2009 Pandemic H1N1 Influenza Virus in Mice

Abstract

Reassortant variant viruses generated between 2009 H1N1 pandemic influenza virus [A(H1N1)pdm09] and endemic swine influenza viruses posed a potential risk to humans. Surprisingly, genetic analysis showed that almost all of these variant viruses contained the M segment from A(H1N1)pdm09, which originated from Eurasian avian-like swine influenza viruses. Studies have shown that the A(H1N1)pdm09 M gene is critical for the transmissibility and pathogenicity of the variant viruses. However, the M gene encodes two proteins, M1 and M2, and which of those plays a more important role in virus pathogenicity remains unknown. In this study, the M1 and M2 genes of A(H1N1)pdm09 were replaced with those of endemic H3N2 swine influenza virus, respectively. The chimeric viruses were rescued and evaluated in vitro and in mice. Both M1 and M2 of H3N2 affected the virus replication in vitro. In mice, the introduction of H3N2 M1 attenuated the chimeric virus, where all the mice survived from the infection, compared with the wild type virus that caused 100 % mortality. However, the chimeric virus containing H3N2 M2 was still virulent to mice, and caused 16.6% mortality, as well as similar body weight loss to the wild type virus infected group. Compared with the wild type virus, the chimeric virus containing H3N2 M1 induced lower levels of inflammatory cytokines and higher levels of anti-inflammatory cytokines, whereas the chimeric virus containing H3N2 M2 induced substantial pro-inflammatory responses, but higher levels of anti-inflammatory cytokines. The study demonstrated that Eurasian avian-like M1 played a more important role than M2 in the pathogenicity of A(H1N1)pdm09 in mice.

The Mobility of Eurasian Avian-like M2 Is Determined by Residue E79 Which Is Essential for Pathogenicity of 2009 Pandemic H1N1 Influenza Virus in Mice

“…Jianmei [32] reported that both M1-41V and M2-27 contribute to replication and pathogenicity. Our previous study indicated that both M1 and M2 of the CA09 strain affects the virulence when a gene segment is exchanged with the H3N2 swine influenza virus [26]. In the present study, we focused on the M2 protein of the (H1N1)pdm09 virus and its role in pathogenicity.…”

“…The wild-types CA09 (CA09-M2-WT) and CA09-M2-E79K were then rescued as previously described [24]. The reverse genetic system of CA09 and the plasmid with the full-length M gene of TX98 were generously provided by Dr. Qinfang Liu from the Shanghai Veterinary Research Institute [25,26]. The two viruses were propagated and titrated on MDCK cells.…”

“…Two groups were inoculated with CA09-M2-WT and CA09-M2-E79K, respectively, and one group with PBS as a control. The mice were intranasally infected with 50 µL of the 10 5.5 TCID 50 virus under slight anesthesia with CO 2 [26,27]. This dose of virus can cause high mortality to mice, which makes it easy to distinguish the difference in pathogenicity of different viruses; the survival rates of the challenge doses of 10 4.5 and 10 5.5 TCID 50 are shown in Figure S3.…”