AIM: To evaluate the relationship between the transcriptional level of IFN-gamma mRNA in peripheral blood mononuclear cells (PBMC) and immune protective response driven by inoculated horses with donkey leukocyte attenuated vaccine of EIAV(DLV), and to elucidate the immune mechanism of DLV. METHODS: A real-time PCR method was established for quantitative detection of IFN-gamma mRNA level from horse PBMCs. Twelve horses were divided into vaccination group, healthy control group, challenging control group and EIAV natural infection group. The transcriptional level and distribution of IFN-gamma mRNA in PBMCs were analyzed. The temperature and other parameters of the inoculated horses were monitored or a daily basis. Horses inoculated with DLV vaccines were challenged post-inoculated 8 months, and the change of transcriptional level of IFN-gamma mRNA during pre/post-challenge was evaluated. RESULTS: Compared with the healthy control and natural infection group. The transcriptional level of IFN-gamma mRNA was much higher in vaccination group (P<0.01), and kept increasing even after challenging with virulent EIAV strains. In the challenging control group, the transcriptional level of IFN-gamma mRNA fluctuated with the development of disease and reduced markedly during febrific episodes. CONCLUSION: This study for the first time reveals that EIAV-attenuated vaccine could induce high level transcription of IFN-gamma mRNA, with is associated closely with immune protective response induced by DLV. This finding provides some clues to elucidate the mechanism of immunity protection of DLV at the molecular level.