Avian Influenza A (H7N9) viruses isolated from patients with mild and fatal infection differ in pathogenicity and induction of cytokines

Highlights

• Influenza A (H7N9) virus results in two types of infection: mild and severe.

• The different results of clinical findings may be related with host susceptibility and characteristics of the virus itself.

• In order to investigate potential pathogenesis of Influenza A (H7N9) virus, we performed pathogenecity and cytokines analysis of two isolates, A/Guangdong/6/2013 H7N9 virus (GD-6) from a patient with a mild infection, and A/Guangdong/7/2013 H7N9 virus (GD-7) from a patient with a fatal infection.

• We found that GD-7 replicated to higher levels than GD-6 in human peripheral blood mononuclear cells (PBMCs), lung tissues, and mice.

• Furthermore, GD-7 infection resulted in more severe lung damage in mice lung tissues than GD-6 infection.

• GD-7 elicited higher levels of interleukin-6 (IL-6) and tumor necrosis factor-α(TNF-α) than GD-6 did. In conclusion, GD-7 was more pathogenic and induced higher levels of proinflammatory cytokines than GD-6 did.

• A critical difference between GD-6 and GD-7 at residue 627 in the PB2 protein with GD-6 having the avian 627E and GD-7 having the mammalian adapted 627K.

• The effect of this difference to the clinical severity needs further molecular genetical and biological studies.

Abstract

Since 2013, a novel Influenza A (H7N9) virus strain has continued to circulate within poultry and causing human disease. Influenza A (H7N9) virus results in two types of infection: mild and severe. The different results of clinical findings may be related with host susceptibility and characteristics of the virus itself. In order to investigate potential pathogenesis of Influenza A (H7N9) virus, we performed pathogenecity and cytokines analysis of two isolates, A/Guangdong/6/2013 H7N9 virus (GD-6) from a patient with a mild infection, and A/Guangdong/7/2013 H7N9 virus (GD-7) from a patient with a fatal infection. We found that GD-7 replicated to higher levels than GD-6 in human peripheral blood mononuclear cells (PBMCs), lung tissues, and mice. Furthermore, GD-7 infection resulted in more severe lung damage in mice lung tissues than GD-6 infection. GD-7 elicited higher levels of interleukin-6 (IL-6) and tumor necrosis factor-α(TNF-α) than GD-6 did. In conclusion, GD-7 was more pathogenic and induced higher levels of proinflammatory cytokines than GD-6 did.

Introduction

In February 2013, a novel avian influenza H7N9 virus (A-H7N9) emerged in Shanghai and was found to infect humans [24]. Subsequently, new H7N9 cases were discovered in Anhui, Zhejiang, Jiangxi, Guangdong, and other Chinese provinces. As of 15 June 2017, a total of 1533 laboratory-confirmed cases of human infection with avian influenza A(H7N9) viruses, with 134 cases reported in the spring of 2013, 306 in 2013–14, 219 in 2014–15, 114 in 2015–16, and 760 in 2016–17, including at least 592 deaths, have been reported to WHO [1]. There were three waves of A-H7N9 infections during this period. From March to May 2013, the pandemic was mainly concentrated in the eastern region of China, with 133 human cases including 45 deaths reported [2]. From October 2013 to May 2014, the pandemic spread to south China and Zhejiang province, where 266 cases were reported [3]. From October 2014 to March 2015, cases were mainly concentrated in the southern region of China, with 118 cases leading to 37 deaths reported [4] (see Table 1).

Human infections with other H7 influenza viruses (H7N2, H7N3, and H7N7) have previously been reported in the Netherlands, USA, Canada, and UK and resulted in conjunctivitis with mild upper respiratory symptoms. Notably, current clinical findings have determined that A-H7N9 results in two types of infection: mild and severe. Mild infections have been presented typically in children and are characterized by flu-like symptoms such as fever, cough, and pharyngeal congestion [5]. On the other hand, severe infections have been typically reported in older adults with rapid illness development that appears as severe pneumonia and rapid development for ARDS, septic shock, and multiple organ failure that leads to death [2]. The different results of clinical findings may be related with host susceptibility and characteristics of the virus itself [6]. Infections with highly pathogenic avian influenza virus such as H5N1 can result in the excessive release of proinflammatory cytokines and chemokines that lead to dysregulation of the host immune response. This “cytokine storm” causes damage to the lung tissue [7], [8]. It was observed that IL-6, IL-8, TNF-α, IL-10 and other cytokines were significantly elevated in the serum of H7N9-infected patients. Furthermore, the levels of these cytokines were significantly higher in the fatal cases of H7N9 influenza compared to that of the mild cases [22]. It seems that the dysregulation of cytokines plays an important role in the course of disease, however, the detailed mechanism needs to be further studied.

In this study, two A-H7N9 strains were isolated from two patients with different clinical outcomes in Guangdong province in late 2013. We examined the pathogenicity as well as the cytokine profiles induced using in vitro, ex vivo, and in vivo studies. The purpose of this study was therefore to investigate potential pathogenesis of H7N9 virus.