Early Immune Signaling among different genera of influenza
Background: The interferon response is one of the early mechanisms of the innate immune system that defends host cells against infection by viruses including Influenza. When a cell becomes infected with a virus, it secretes interferons as a signaling molecule that then activates the transcription of hundreds of genes with anti-viral effects. Some of these (PKR, OAS) are well-studied, but many of the functions are poorly understood and potentially represent new pathways to target for antiviral therapies. The timing and magnitude of the response has important implications for the course and severity of disease so characterizing the response is paramount to understanding treatment.
Methods: We incubated small-cell lung cancer Calu3 cells with infection media containing either a well-characterized laboratory strain of influenza A, B or C or a mock control. Cell lysates were collected at the indicated time points and total RNA was extracted. We then performed reverse transcription using poly-T primers and quantified transcriptomes of key interferon pathogen genes including IFN-B, IFN-L and ISG15 using qRT-PCR. We chose these genes because of IFN-B and IFN-L’s known importance in Influenza A infection and ISG15 inhibition by Influenza B.
Results: CALU3 cells infected with Influenza C produced a more robust IFN-B and IFN-L response than the other two strains tested. The cells infected with Influenza B had a more robust ISG15 response than Influenza C.
Conclusions: These results indicate that Influenza A and B have mechanisms to evade early mechanisms of the interferon response compared to Influenza C. Influenza B, however, appears to be lacking mechanisms to evade transcriptional induction ISG15 as well as the other genera. These findings provide implications for further exploration of unique mechanisms of immune evasion for Influenza genera. Based on this data, we suggest cell lines with knockouts for the genes tested to ascertain how big of a role they have in the development and severity of Influenza strains. We could support our transcriptional findings with protein level data using Western blotting of phosphorylated STAT1, a transcription factor that plays an essential role in responses to interferons, to quantify the activation of signaling pathways downstream of interferon receptors.