Pericyte dysfunction alone may be insufficient to drive tick-borne orthoflavivirus non-structural protein 1-mediated microvascular permeability.

The emerging tick-borne flaviviruses Alkhumra haemorrhagic fever virus (AHFV) and Kyasanur Forest disease virus (KFDV) can cause severe haemorrhagic disease, yet the mechanisms driving this vascular leakage remain unclear. The microvascular capillaries and post-capillary venules affected during orthoflavivirus-related haemorrhagic disease consist of an endothelial cell (EC) barrier ensheathed in and supported by perivascular cells (pericytes), and we recently identified a critical role for pericytes in amplifying dengue microvascular dysfunction. The orthoflavivirus non-structural protein 1 (NS1) has been implicated in endothelial dysfunction and vascular leakage for several tick- and mosquito-borne flaviviruses. Here, we examined whether NS1 from AHFV and KFDV disrupts microvascular barrier integrity in pericyte-EC cocultures. We found AHFV and KFDV NS1 to disrupt the ability of pericytes to support EC function, which is required for maintenance of the microvascular barrier. However, under our experimental conditions, we detected no endothelial hyperpermeability upon NS1 treatment in ECs cultured alone or in combination with pericytes. Our findings suggest that the concomitant impairment of both EC and pericyte function may be required for NS1 to induce microvascular hyperpermeability. Our work highlights the potentially synergistic effects of microvascular cells during orthoflavivirus haemorrhage and emphasizes the need for further work into the mechanisms of vascular dysfunction during AHFV and KFDV infection.