Endothelial cell infection in vivo by equine infectious anaemia virus

This study identifies vascular endothelial cells as a previously unknown site of equine infectious anaemia virus (EIAV) replication in infected horses. Researchers used in situ hybridization combined with immunohistochemistry to detect EIAV-infected endothelial cells and macrophages in three horses infected with either virulent (Wyoming strain) or weakly virulent (tissue culture-adapted WSU5 strain) EIAV. All infected horses developed characteristic clinical signs including fever and thrombocytopenia. Viral RNA was detected in endothelial cells throughout multiple tissues including spleen, liver, intestine, and colon. While tissue macrophages remained the predominant infected cell type, endothelial cell infection was widespread. Notably, both virus strains infected similar cell types in vivo despite their different tropism patterns in cell culture, suggesting that differences in virulence are not determined by qualitative differences in cellular tropism. The authors propose that endothelial cell infection may contribute to EIAV-associated thrombocytopenia through subtle cellular damage promoting platelet adherence, though direct vascular lesions were not histologically evident.

Key findings

• Vascular endothelial cells are identified as a new in vivo site of productive EIAV replication, in addition to previously recognized tissue macrophages
• Both virulent Wyoming strain and attenuated tissue culture-adapted strain infected endothelial cells and macrophages similarly in vivo, despite different in vitro tropism patterns
• Endothelial cell infection does not appear to be a determinant of EIAV virulence, as both high and low virulence strains showed similar cellular tropism
• Qualitative differences in cellular tropism between virus strains do not account for observed virulence differences, suggesting virulence factors may reside in viral long terminal repeats