Suppression of HIV-1 reverse transcriptase activity by mycoplasma contamination of cell cultures

The detection of HIV-1 in human peripheral blood lymphocytes is routinely carried out by cocultivation of test cells with normal peripheral blood mononuclear cells (PBMC). The presence of virus is evidenced by cytologic observation of syncytia or by detecting viral reverse transcriptase (RT) and/or p24 antigen in the culture supernatant fluid. Syncytia formation is almost always associated with the presence of virus as measured by RT, although many RT-positive cultures do not form syncytia. As part of a large screening program, we identified three cultures that showed syncytia but were RT negative. The basis for these discrepant observations was contamination of cultures with mycoplasma that interfered with the RT assay and thereby obscured virus detection. Treatment of cultures with BM-cycline removed mycoplasma contamination and restored RT activity. The present findings indicate the need for caution in the interpretation of negative RT results during HIV-1 isolation and especially in cultures that show evidence of syncytia formation.