Is LM7 a new human retrovirus or a mycoplasma virion?

A putative retrovirus called LM7 was recently isolated from a patient with MS. This retrovirus was detected in LM7 and LM711 cultured human leptomeningeal cells. In the present work, nucleic acids from LM711 cell culture supernatants were purified and subjected to avian myeloblastosis viral (AMV) reverse transcriptase and to random polymerase chain reaction (rPCR) in order to characterize the genomic material of LM7 virions. Analysis of reverse transcription products allowed the detection of an approximately 14 kb ribonucleic acid in all LM711 cell culture supernatants. However, sequencing of rPCR-amplified molecules as well as RNA blotting data showed essentially that all tested cells producing LM7 particles were infected with mycoplasma. Moreover, purification of LM7 particles onto a linear sucrose density gradient established that the 14 kb nucleic acid was always associated with the 1.19-1.21 g ml-1 sucrose fractions, which are known to correspond to the buoyant density of mycoplasma. In addition, no viral genomic RNA was detected in the 1.17 g ml-1 sucrose fraction containing the low reverse transcription activity. These results strongly suggest that microscopic images and serological data could be related to mycoplasma and/or to a virion associated with the bacteria. The LM7 particle might be a new and additional enveloped virus able to infect Mycoplasma hyorhinis hosts. Thus, for instance, it would be presumptuous to assert, with our current understanding, that the LM7 virion is one of the causal agents of MS in humans.