In order to determine whether peripheral blood mononuclear cells (PBMC) contain proviral DNA or double-stranded replicative forms of TT virus (TTV) and to define which cell subset harbors TTV, we analyzed 126 PBMC DNA samples by PCR, using the NG059/NG061/NG063 and the T801/T935 primer sets. TTV sequences were detected in nearly 20%(25/126) of PBMC DNA samples. Analysis of PBMC subsets revealed that TTV was preferentially distributed in CD19(+) cells. TTV DNA was also detected in CD3(+)/CD19(+) double-depleted cells but was undetectable in CD3(+) cells. After degradation of single-stranded DNA using mung bean nuclease (MBN), TTV could not be detected in previously TTV-positive PBMC DNA samples nor in DNA from CD19+ cells, CD3(+)-depleted, and CD3(+)/CD19(+) double-depleted cells, indicating the lack of TTV DNA integration and the absence of viral double-stranded replicative intermediates in PBMC or PBMC subset cells. Our data indicate that PBMC and PBMC subsets are not the major sites of TTV replication. J. Med. Virol. 66:276-284, 2002. (C) 2002 Wiley-Liss, Inc.