Identification of target cells of a European equine arteritis virus strain in experimentally infected ponies

Currently, little is known on the cellular pathogenesis of equine arteritis virus (EAV). The purpose of the present study was to identify the target cells in ponies experimentally inoculated with EAV 08P178 (EU, clade-1). EAV-target organs (respiratory tissues with associated lymphoid tissues and large intestines), collected at 3 and 7 days post inoculation (dpi) and with virus titers ≥ 105.0 TCID50/g, were processed with double immunofluorescence staining for the simultaneous detection of EAV N-protein and one of the following cell markers: CD172a (myeloid cells), CD3 (T lymphocytes), IgM (B lymphocytes) and von Willebrand factor (endothelial cells). In the different analyzed organs, 31-58% and 47-63% of the EAV-positive cells were mononuclear leukocytes (mainly CD172a+ followed by CD3+) at 3 and 7 dpi, respectively. EAV-positive endothelial cells were not detected in 3.200 large blood vessels (≥3 endothelial cells/vessel cross section). However, in terminal capillaries (1-2 endothelial cells/vessel cross section) of the different organs, 15-51% of the endothelial cells were EAV-positive. In conclusion, the present study demonstrates that EAV 08P178 (i) has a main tropism for CD172a+ and CD3+ mononuclear leukocytes and (ii) infects a large number of endothelial cells in terminal capillaries. EAV 08P178 infection in capillaries is most probably the cause of an increased vascular permeability leading to leakage of fluid (edema-serous exudate) but not to severe vasculitis and hemorrhages.