Association of Increased Pathogenicity of Asian H5N1 Highly Pathogenic Avian Influenza Viruses in Chickens with Highly Efficient Viral Replication Accompanied by Early Destruction of Innate Immune Responses

Abstract

The Asian H5N1 highly pathogenic avian influenza (HPAI) viruses have been increasing in pathogenicity in diverse avian species since 1996 and are now widespread in Asian, European, and African countries. To better understand the basis of the increased pathogenicity of recent Asian H5N1 HPAI viruses in chickens, we compared the fevers and mean death times (MDTs) of chickens infected with the Asian H5N1 A/chicken/Yamaguchi/7/04 (CkYM7) strain with those infected with the H5N1 Duck/Yokohama/aq10/03 (DkYK10) strain, using a wireless thermosensor. Asian H5N1 CkYM7 caused peracute death in chickens before fever could be induced, whereas DkYK10 virus induced high fevers and had a long MDT. Real-time PCR analyses of cytokine mRNA expressions showed that CkYM7 quickly induced antiviral and proinflammatory cytokine mRNA expressions at 24 h postinfection (hpi) that suddenly decreased at 32 hpi. In contrast, these cytokine mRNA expressions increased at 24 hpi in the DkYK10 group, but decreased from 48 hpi onward to levels similar to those resulting from infection with the low-pathogenicity H5N2 A/chicken/Ibaraki/1/2004 strain. Sequential titrations of viruses in lungs, spleens, and kidneys demonstrated that CkYM7 replicated rapidly and efficiently in infected chickens and that the viral titers were more than twofold higher than those of DkYK10. CkYM7 preferentially and efficiently replicated in macrophages and vascular endothelial cells, while DkYK10 grew moderately in macrophages. These results indicate that the increased pathogenicity in chickens of the recent Asian H5N1 HPAI viruses may be associated with extremely rapid and high replication of the virus in macrophages and vascular endothelial cells, which resulted in disruption of the thermoregulation system and innate immune responses.

Inhibition of Reactive Oxygen Species Production Ameliorates Inflammation Induced by Influenza A Viruses via Upregulation of SOCS1 and SOCS3

“…Other literature suggests that suppression of the cytokine response alone may not be sufficient to provide adequate protection, as has been noted in mice infected with human H5N1 isolates (41). On the other hand, however, there is clear evidence of hypercytokinemia in H5N1-and H7N9-infected humans (5-7) and chickens (39). Moreover, functional microarray analysis of lung samples obtained from infected ferrets has shown overexpression of genes involved in IFN signaling, especially CXCL10 (42).…”

The Pathogenicity and Host Immune Response Associated with H5N1 Highly Pathogenic Avian Influenza Virus in Quail

“…However, in the present study, infection caused a decrease in the expression of IFN-γ in chicken PBMC. Similarly, Suzuki et al [18] found that IFN-γ decreased in the lung of chicken infected with HPAIV A/chicken/Yamaguchi/7/2004 (H5N1). Both this virus and the virus used in our study were isolated in Asia in recent years.…”

“…Both this virus and the virus used in our study were isolated in Asia in recent years. These recent Asian H5N1 viruses are thought to cause early destruction of the innate immune response in chicken [18], and have been increasing in pathogenicity in diverse avian species. On the other hand, in quail PBMC, the increase of IFN-γ expression appears to have activated the antiviral function in the innate immune response.…”

“…Th1 and pro-inflammatory responses were observed in the lung and spleen of 4-week-old chickens infected with a humanderived H5N1 HPAIV [11]. Furthermore, a recently emerged Asian H5N1 HPAIV was shown to quickly induce antiviral and pro-inflammatory cytokines in the lung of 4-week-old chickens as early as 24 hr after inoculation, but 8 hr later, just before death, their mRNA levels decreased dramatically [18]. In Pekin duck infected with three H5N1 strains, younger ducks expressed cytokine mRNA more weakly than older ducks, which were more resistant to the pathological conditions caused by HPAIV infection [17].…”

“…On the other hand, the role of cytokines in the pathology caused by H5N1 HPAIVs in avian species is less well understood. To date, several studies have shown that different avian species exhibit different pathologies and cytokine responses from H5N1 virus infection [7,11,15,17,18]. Type I interferon (IFN) was induced by H5N1 HPAIV in lung, spleen and plasma of 6-week-old chickens [15].…”