Endotoxin treatment of equine infectious anaemia virus-infected horse macrophage cultures decreases production of infectious virus.

Lentiviruses replicate in cells of the immune system, and activation of immune cells has been shown to modulate virus replication. To determine the effects of macrophage activation on replication of equine infectious anaemia virus (EIAV), primary horse macrophage cultures (HMCs) were established from 20 different horses, infected with an avirulent strain of EIAV, and stimulated with 5 microg/ml of bacterial endotoxin. Supernatants collected from HMCs were assayed for the presence of tumour necrosis factor (TNF-alpha) and for production of infectious virus. Results indicated that EIAV replication in vitro varied significantly (P < or = 0.0001) from horse to horse, regardless of the treatment of HMCs. Also, EIAV replication was significantly (P < or = 0.0001) decreased in HMCs stimulated with bacterial endotoxin as compared to untreated HMCs. No significant correlation was found between virus replication and production of TNF-alpha following treatment of virus-infected cells with bacterial endotoxin. However, when HMCs were treated with endotoxin prior to virus infection, inhibition of EIAV replication was proportional to increasing levels of endotoxin. PCR and RT-PCR were used to amplify EIAV proviral DNA and mRNA sequences, respectively, at various time-points following infection. The results indicated that the early events of EIAV replication, up to and including transcription of multiple-spliced mRNAs, were not inhibited by treatment of EIAV-infected macrophages with bacterial endotoxin. This suggests that endotoxin treatment inhibits a posttranscriptional step in the virus replication cycle.