Background: NF-kB is a family of transcription factors with pleiotropic influence across broad cellular responses. NFkB1 (p50) null mice are viable and mature into adulthood. Whilst p50 is important for immunity to bacterial and parasitic infections, its role in the control of viral infection has not been previously investigated. Intriguingly, we have discovered a critical role for p50 in host survival during systemic infection with the non-cytopathic Lymphocytic Choriomeningitis Virus (LCMV).
Methods and Results: p50-/- mice rapidly succumbed to LCMV infection with 100% lethality, whereas wild-type (WT) mice were asymptomatic. Death resulted from respiratory distress induced by severe pulmonary endothelial leakage, as measured by Evan’s blue extravasation assay and histology. There were no differences in organ viral titres between p50-/- and WT mice. Immune chimera experiments revealed that the fatal phenotype is intrinsic to the p50-/- stroma, occurring irrespective to the concomitant absence of p50 in the hematopoietic compartment. WT and p50-/- animals produced similar amounts pro-inflammatory cytokines in lungs and sera, as measured by Luminex cytokine assays. Antibody-mediated depletion of key molecules (TNF, VEGF, Type I and II IFNs) or immune cells (macrophages, neutrophils) also failed to prevent lethality. RNA-seq of pulmonary endothelial cells from naïve and LCMV-infected animals revealed hyper-activation in p50-/- mice marked by significant increases in the expression of, immune adhesion molecules: Vcam1, Icam1, E-sel, P-sel; cytokines: Cxcl1, Ccl2 ; and pathogen recognition receptors: RigI, Mda5 and Mavs.
Conclusion: Our findings reveal a critical and previously unknown role for p50 in the maintenance of endothelial integrity during infection. Our data indicates the p50-/- endothelium is hyper-activated and exacerbates innate responses to viral infection, driving leakage and lethality. While components of the immune system are likely involved, this phenotype is completely dependent upon a lack of p50 in the non-immune stroma. These findings require further investigation that may offer insights into the signalling pathways that precede dangerous vascular leakage in human infections such as Dengue virus.