Ebola virus infection of Flt3-dependent, conventional dendritic cells and antigen cross-presentation leads to high levels of T-cell activation
Severe Ebola virus disease (EVD) is characterized by excess, dysregulated T-cell activation and high levels of inflammation. Previous studies have described that in vitro EBOV infection of monocyte-derived DCs (moDCs) inhibits DC maturation resulting in suppression of T-cell activation. However, it is unknown how other DC subsets distinct from moDCs respond to EBOV infection. To better understand how DCs initiate T cell activation during EBOV infection, we assessed the response of FMS-like tyrosine kinase 3 (Flt3)-dependent, conventional mouse DCs (cDCs) to EBOV infection, and developed a DC-T-cell co-culture system utilizing a recombinant EBOV expressing the model antigen ovalbumin. Our findings suggested that, in contrast to moDCs, cDC2 and cDC1 were poorly infected with EBOV, although both infected and bystander cDCs displayed high levels of activation. DCs were able to activate CD8 T cells via cross-presentation of EBOV antigens obtained from cell debris of EBOV-infected cells. Of note, rather than interfering with cross-presentation, EBOV infection enhanced the cross-presentation capacity of DCs. Our findings indicate that EBOV infection of Flt3-dependent cDCs, results in activation rather than inhibition leading to high levels of CD8 T-cell activation. With that we propose a mechanistic explanation for the excess T-cell activation observed in severe human EVD.