GFP Labelled Human Metapneumovirus

The innate sensing system is equipped with PRRs that specifically recognize various pathogen molecular structures (PAMPs). This leads to the induction of antiviral genes and the inhibition of viral growth. Human metapneumovirus (HMPV) is a major respiratory virus that causes upper and lower respiratory tract infections in children. Here, researchers show that upon HMPV infection, the innate sensing system senses viral RNA via the RIG-I sensor, which induces CEACAM1 expression. Researchers further show that CEACAM1 is induced via binding of IRF3 to the CEACAM1 promoter. Induction of CEACAM1 suppresses viral load by inhibiting the translation machinery in infected cells in a SHP2-dependent manner. Together, these studies demonstrate that HMPV-infected cells upregulate CEACAM1 to limit HMPV infection.

Here, to investigate whether HPMV infection affects the expression of various natural killer (NK) cell ligands, A549 cells were infected with HMPV. After 48 hours of infection, cells were verified to be infected using qRT-PCR (Figure 1a) or infection with a recombinant HMPV virus expressing green fluorescent protein GFP (GFP HMPV) (Figure 1b). Next, mock-infected and infected cells were stained for the expression of various immune ligands, such as CEACAM1 (Figures 1c and 1d, respectively). Virtually 100% of the cells were infected, as shown in Figure 1d. A significant induction of CEACAM1 expression following HMPV infection was also observed (Figures 1d and 1e). Analysis of the kinetics of CEACAM1 expression showed that protein expression was visible as early as 6 hours post-infection, peaking at 12 hours post-infection (Figure 1f). An increase in CEACAM1 mRNA was also observed after HMPV infection (Figure 1g).

Figure 1. Expression of CEACAM1 in A549 cell line following HMPV infection. (Diab M, et al., 2016)