No Definite Evidence for Human Endogenous Retroviral HERV-W and HERV-H RNAS in Plasma of Latvian Patients Suffering from Multiple Sclerosis and Other Neurological Diseases

Multiple sclerosis (MS) is a neurological disease of unknown aetiology. Several research groups reported an increased level of human endogenous retroviruses HERV-W and HERV-H RNAs in cerebrospinal fluid, plasma and supernatants of cell cultures from MS individuals. To quantify the abundance of extracellular virion-associated HERV, RNAs in blood, plasma samples from Latvian MS patients, patients with other neurological diseases (OND), as well as blood donors (BD), were retrospectively studied by using both our previously published and newly developed quantitative Real-time reverse transcription PCR assays (QPCRs) targeting different polymerase (pol) gene regions of HERV-W and HERV-H. Unspecific signals due to incomplete removal of DNA were monitored by running the assays with and without reverse transcription (RT±) in parallel. According to our score, a few MS, OND and healthy controls gave borderline signals simultaneously with both newly developed HERV-H and HERV-W QPCRs, but the rest were negative. All borderline positive samples also had small amounts of non-retroviral cellular mRNA with possible origin from cell-free circulating RNA fragments, apoptotic bodies or exosomes, which can mimic the previously described virus-like particles. The results do not confirm the previous reports on prevalence of HERV-H or-W virion-associated RNA in plasma of MS patients.