Evaluation of intravirion human immunodeficiency virus type 1 RNA degradation activity in saliva by an RNA cleavage quantification method

Abstract

AbstractIntroductionAlthough human immunodeficiency virus type 1 (HIV‐1) infection through blood, breast milk, semen, and vaginal secretions has been established, no report has clearly demonstrated HIV‐1 infection through saliva. We postulated that a low or absent infectivity of HIV‐1 in saliva is due to the damage of viral RNA in virions. To test this hypothesis, we developed an RNA cleavage quantification method.Materials and methodsA part of the gag gene was reverse transcribed from HIV‐1 RNA extracted from saliva‐treated virus, and the cDNA product was analyzed by quantitative real‐time PCR at three positions that were located at various distances from the reverse transcription (RT) start site. The slope of plots of cycle threshold value vs distance between the RT start site and the primer‐binding position was used to evaluate the degree of RNA damage.ResultsWhen free HIV‐1 RNA was incubated in saliva, the RNA became undetectable within 5 minutes; however, when virions were incubated, cleavage of the viral RNA occurred at a much slower rate. Although heat treatment at 70°C for 20 minutes did not influence the ability of saliva to cleave free HIV‐1 RNA, it completely suppressed the RNA cleavage activity within the viral envelope, suggesting that viral structure was loosen or destroyed by thermolabile factors and then intravirion RNA was digested by salivary ribonucleases.ConclusionsWe detected thermolabile intravirion RNA cleavage activity in saliva. This activity may be related to a poor infectivity of HIV‐1 in saliva.