Aberrant expression of immunoglobulin mRNA in bovine leukemia virus-infected cattle

Our objective was to determine whether bovine leukemia virus (BLV) integration and expression affect the expression of host genes that function in immune responses and cell proliferation. Freshly isolated mIgM+ cells obtained from BLV-infected cows with persistent lymphocytosis (PL) expressed increased Ig-μ mRNA and decreased mRNA for Ig-λ relative to infected and uninfected animals that had normal peripheral lymphocyte counts. In contrast, there was no correlation between BLV-infection status and expression of major histocompatibility complex (Mhc) Class I or Class II genes. The induction of BLV expression in mIgM+ cells from animals with PL did not affect significantly the levels of Mhc Class I, Class II, Ig-μ or Ig-λ mRNA. Phorbol ester-induced c-fos mRNA expression was greater in the BLV-infected cell line BL3∗ than the uninfected parental cell line BL3°. However, the level of c-fos expression did not appear different compared with its induction in peripheral blood B cells from seronegative animals and animals with PL. We conclude that the BLV early and late phase proteins have no effect on Ig or Mhc mRNA levels, but that freshly isolated mIgM+ cells from PL animals constitutively express increased Ig-μ and decreased Ig-λ mRNA. These data suggest that the increase in Ig-μ and mIgM on B cells from PL cows is related to a differentiation state rather than trans-activation by BLV.