Short-termed expression of interleukin-12 during experimental BLV infection may direct disease progression to persistent lymphocytosis

In this study an attempt was made to elucidate cellular response cytokine expression upon experimental bovine leukemia virus (BLV) infection in cattle. Progression of infection was monitored by BLV gp51 mRNA expression or DNA amplification by RT–PCR or PCR, respectively, to detect provirus infected cells. Antibodies to BLV were detected by an agar gel immuno-diffusion (AGID) test in 5 weeks and persistent lymphocytosis (PL+) was established in all four BLV-infected animals in 24 weeks after infection. At the initial stage of infection a strong cellular immune response was induced mediated by IL-12p40 mRNA expression. Short-termed IL-12p40 expression was observed in peripheral blood mononuclear cells (PBMC) in two out of four infected animals following 1–3 weeks after infection, while viral mRNA expression was observed 2 weeks following infection. Expression of genes coding for the pro-inflammatory TNFα, IL-1β and cellular response cytokines IFNγ and IL-2 was detected beginning with the second and third week after infection in all BLV-infected animals. However, IFNγ expression significantly decreased in 12 weeks after infection in three animals while IL-10 message initially detected 3 weeks after infection increased by 12 weeks and persisted. The observed immediate short-termed cell mediated immune response characterized by IL-12p40 and IFNγ expression followed by an early shift to an IL-10 induced humoral response, may change the cytokine balance and direct disease progression to the PL+ stage.