PA-X protein of H1N1 subtype influenza virus disables the nasal mucosal dendritic cells for strengthening virulence

ABSTRACT

PA-X protein arises from a ribosomal frameshift in the PA of influenza A virus (IAV). However, the immune regulatory effect of the PA-X protein of H1N1 viruses on the nasal mucosal system remains unclear. Here, a PA-X deficient H1N1 rPR8 viral strain (rPR8-△PAX) was generated and its pathogenicity was determined. The results showed that PA-X was a pro-virulence factor in mice. Furthermore, it reduced the ability of H1N1 viruses to infect dendritic cells (DCs), the regulator of the mucosal immune system, but not non-immune cells (DF-1 and Calu-3). Following intranasal infection of mice, CCL20, a chemokine that monitors the recruitment of submucosal DCs, was downregulated by PA-X, resulting in an inhibition of the recruitment of CD11b⁺ DCs to submucosa. It also attenuated the migration of CCR7⁺ DCs to cervical lymph nodes and inhibited DC maturation with low MHC II and CD40 expression. Moreover, PA-X suppressed the maturation of phenotypic markers (CD80, CD86, CD40, and MHC II) and the levels of secreted pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) while enhancing endocytosis and levels of anti-inflammatory IL-10 in vitro, suggesting an impaired maturation of DCs that the key step for the activation of downstream immune responses. These findings suggested that the PA-X protein played a critical role in escaping the immune response of nasal mucosal DCs for increasing the virulence of H1N1 viruses.

KEYWORDS:

• Influenza A virus
• H1N1
• PA-X protein
• dendritic cells
• innate immunity
• virulence

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability

All data are available from the authors upon reasonable request.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/21505594.2022.2139474

Additional information

Funding

This work was supported by the National Key Research and Development Program of China (2021YFD1800202), the National Natural Science Foundation of China (32172942), the Jiangsu Provincial Natural Science Fund for Excellent Young Scholars (BK20200105), the Agricultural Science and Technology Independent Innovation Fund of Jiangsu Province (CX(20)3092), Yangzhou University Interdisciplinary Research Foundation for Veterinary Medicine Discipline of Targeted Support (yzuxk202004), the High-Level Talent Support Plan of Yangzhou University [(2018) NO.10, (2020) NO.28], the Priority Academic Program Development of Jiangsu Higher Education (PAPD), and Jiangsu Province Postgraduate Research and Practice Innovation Program (No. KYCX21-3276).]