Bovine leukemia virus (BLV) is a retrovirus that affects primarily milky cows.Animals serologically positive to BLV show a Th1 cytokine profile with a predominance of interferon gamma (IFN-γ).IFN-γ has antiviral activity through mechanisms such as resistance to infection, inhibition of viral replication and apoptosis.The objective of this work was to determine the transcription levels of IFN-γ and its relationship with proviral load and persistent lymphocytosis in a population of Holstein cows of the province of Antioquia, Colombia.IFN-γ transcription levels were evaluated by qPCR in 140 Holstein cows.A one-way analysis of variance and a Student's t test were used to evaluate the differences between the means.The amount of IFN-γ mRNA found in BLV-positive cows was lower than in BLV-negative cows.Moreover, in the group of infected cows a lower level of IFN-γ mRNA expression was found in BLV and persistent lymphocytosis cows (BLV+PL) compared with BLV and aleukemia cows (BLV+AL).The level of IFN-γ mRNA expression was lower in cows with high proviral load (HPL) compared to cows with low proviral load (LPL).BLV infection is related to abnormal expression of IFN-γ mRNA, although IFN-γ has antiviral activity, its expression is affected by high proviral load.