IL2 and deltaretrovirus infections: In addition, mRNA of cytokines such as interleukin-2 (IL-2), IL-12, and γ-interferon increase in peripheral blood mononuclear cells (PBMCs) of animals during early stages of BLV infection and decrease in PBMCs from animals with later stages of BLV infection (Pyeon et al., 1996; Yakobson et al., 1998).