Replication ability in vitro and in vivo of equine infectious anemia virusavirulent Japanese strain

An attenuated equine infectious anemia virus (EIAV), V26, was previously pr epared by 50 passages of the Japanese virulent strain V70 in primary horse macrophage culture. The horses inoculated with this V26 virus were shown to raise neutralizing antibodies against V70 without any viremia. Here, we in vestigated the in vitro and in vivo replication ability of V26. Comparison of the long-terminal repeat (LTR) sequences between V26 and V70 revealed a large insertion within the LTR U3 hypervariable region of V26. V26 with the mutation in the LTR showed much higher promoter activity in vitro than V70 . This is consistent with the much higher replication rate of V26 in horse primary macrophage cultures compared with V70. In sharp contrast, we failed to identify the V26-specific LTR sequence by PCR, at least in sequential s amples of plasma or peripheral blood mononuclear calls derived from three h orses until day 62 after V26 inoculation. In contrast, antibody responses t o EIAV were observed in all horses. The results suggest that the replicatio n ability of V26 in vivo is extremely low. When one of the horses was subse quently challenged with cell-associated V70, it was found that the horse be came PCR positive for EIAV. There was no LTR mutation in EIAV genome in sam ples periodically prepared from the V70-challenged horse. Thus it was sugge sted that the LTR mutation in EIAV, which occurs during serial passage in v itro, affects EIAV replication in vitro and in vivo. (C) 2000 Academic Pres s.