Higher expression levels of alternatively spliced pX mRNA in human T lymphotropic virus type I asymptomatic carriers positive for antibodies to p40tax protein.

cDNA of human T lymphotropic virus type I (HTLV-I) pX gene mRNA expressed in peripheral blood lymphocytes of asymptomatic carriers was sequenced. One cDNA clone contained a novel splicing acceptor site, indicating an unidentified form of pX mRNA: pX delta 17 delta 37. All 21 asymptomatic carriers expressed some level of alternatively spliced pX mRNA (pX, pX delta 17, p21rex, orfII, or pX delta 17 delta 37). pX and pX delta 17 were the dominant mRNA species among the five pX mRNAs. All pX mRNAs but orfII correlated significantly with amounts of provirus DNA (P < .05). Levels of provirus DNA and pX mRNAs were significantly higher in anti-p40tax-positive carriers than in negative ones. These observations suggest that the pX mRNAs are expressed ubiquitously, with a complex pattern of splicing, and that the presence of anti-p40tax may serve as a marker for a higher virus load and viral replication levels in asymptomatic HTLV-I carriers.