TT virus (TTV) leads associated with different peripheral blood cell typesand evidence for TTV replication in activated mononuclear cells

TT virus (TTV) loads associated with the peripheral blood cells of seven pa tients known to carry the virus in plasma were investigated by real-time PC R. Whereas red cells/platelets were uniformly negative, six and four patien ts yielded positive peripheral blood mononuclear cells (PBMCs) and polymorp honuclear leukocytes, respectively, but viral titres were generally low. Fr actionation of PBMCs into monocyte- and B, T4, and T8 lymphocyte-enriched s ubpopulations showed no pattern in the viral loads that might suggest the p referential association of TTV to one or more specific cell types. TTV-nega tive PBMCs absorbed measurable amounts of virus when incubated with infecte d plasma at 4 degreesC. Furthermore, cultures of TTV-negative phytohaemaggl utinin-stimulated PBMCs exposed in vitro to virus-positive plasma and faeca l extracts released considerable levels of infectious TTV into the supernat ant fluid and the same was true for TTV-positive stimulated PBMCs. These re sults indicate that, whereas freshly harvested resting PBMCs seem to produc e little, if any TTV, stimulated PBMCs actively replicate the virus. (C) 20 01 Wiley-Liss, Inc.