Isolation of a C-type retrovirus from an HIV infected cell line.

A study by electron microscopy of HUT 78 cells infected with the ARV-2 strain of HIV-1 revealed, in addition to virions having the characteristic morphology of a lentivirus, the presence of numerous C-type particles, suggesting that the analysed specimen might in fact contain two different viruses. In order to further investigate this observation, the cell culture supernatant was filtered and mixed at serial dilutions with uninfected HUT 78 cells. In this way, it was possible to obtain cells producing only virions with C-type morphology and a Mn++ dependent reverse transcriptase activity which in a sucrose gradient was found to peak at a buoyant density of 1.16 g/cm3. The RNA purified from the culture medium was not detected by reference DNA probes for either HIV-1 and -2 or HTLV-I and -II. In an indirect immunofluorescence assay, sera from patients seropositive for these human retroviruses failed to recognize any antigen in the cells producing only the C-type particles. Using the same technique, plasma samples from 100 blood donors also gave negative results. The presence of this retrovirus could be the result of previous laboratory contamination but the possibility that it is indeed a human virus has to be considered.