Influenza A viruses pose a constant potential threat to human health. In view of the innate antiviral activity of interferons (IFNs) and their potential use as anti-influenza agents, it is important to know whether viral resistance to these antiviral proteins can arise. To examine the likelihood of emergence of IFN-λ1-resistant H1N1 variants, we serially passaged the A/California/04/09 (H1N1) strain in a human lung epithelial cell line (Calu-3) in the presence of increasing concentrations of recombinant IFN-λ1 protein. To monitor changes associated with adaptation of this virus to growth in Calu-3 cells, we also passaged the wild-type virus in the absence of IFN-λ1. Under IFN-λ1 selective pressure, the parental virus developed two neuraminidase (NA) mutations, S79L and K331N, which significantly reduced NA enzyme activity (↓1.4-fold) and sensitivity to IFN-λ1 (↓˃20-fold), respectively. These changes were not associated with a reduction in viral replication levels. Mutants carrying either K331N alone or S79L and K331N together induced weaker phosphorylation of IFN regulatory factor 3 (IRF3), and, as a consequence, much lower expression of the IFN genes (IFNB1, IFNL1 and IFNL2/3) and proteins (IFN-λ1 and IFN-λ2/3). The lower levels of IFN expression correlated with weaker induction of tyrosine-phosphorylated STAT1 and reduced RIG-I protein levels. Our findings demonstrate that influenza viruses can develop increased resistance to the antiviral activity of type III interferons.
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机译：甲型流感病毒不断威胁着人类健康。考虑到干扰素（IFN）的先天抗病毒活性及其作为抗流感药的潜在用途，重要的是要知道是否会出现对这些抗病毒蛋白的病毒抗药性。为了检查出现IFN-λ1耐药H1N1变体的可能性，我们在重组浓度不断增加的情况下，在人肺上皮细胞系（Calu-3）中连续传代了A / California / 04/09（H1N1）株IFN-λ1蛋白。为了监测与此病毒适应Calu-3细胞生长相关的变化，我们还在没有IFN-λ1的情况下传代了野生型病毒。在IFN-λ1选择性压力下，亲本病毒产生了两个神经氨酸酶（NA）突变，即S79L和K331N，分别显着降低了NA酶的活性（↓1.4倍）和对IFN-λ1的敏感性（↓˃20倍）。这些变化与病毒复制水平的降低无关。单独携带K331N或S79L和K331N的突变体共同诱导IFN调节因子3（IRF3）的磷酸化较弱，因此，IFN基因（IFNB1，IFNL1和IFNL2 / 3）和蛋白质（IFN-λ1）的表达要低得多。和IFN-λ2/ 3）。较低水平的IFN表达与酪氨酸磷酸化STAT1的诱导较弱和RIG-1蛋白水平降低有关。我们的发现表明，流感病毒可以增强对III型干扰素的抗病毒活性的抵抗力。
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