FIG. 1.
(A) Protocol used to alter the cell tropism of EIAV. A highly virulent, macrophage-tropic strain of EIAV (EIAVwyo) was used to infect primary MDMs. Supernatants were collected and passaged into fresh MDMs nine additional times. Concurrently, unsuccessful attempts were made to passage EIAVwyo stocks into primary equine endothelial cells (UVECs) and equine fibroblast cells (ED cells). Upon 10 MDM passages, viral stocks replicated in UVECs but the stocks still did not replicate in ED cells. Following 10 passages in UVECs, stocks were able to replicate in ED cells. 3′ TM and the LTR U3 sequences were RT-PCR amplified at passages noted and were analyzed as described below. (B) The 450-bp region of the EIAV genome amplified. This region encompassed the last 217 bp of TM, a 17-nucleotide spacer, and the 202 bp of the LTR U3.