SPONTANEOUS LYMPHOCYTE-PROLIFERATION IN HTLV-I/II INFECTION REFLECTS PREFERENTIAL ACTIVATION OF CD8 AND CD16/56 CELL SUBSETS

Previous studies have shown that lymphocytes from HTLV-infected persons spontaneously proliferate when cultured in vitro. We investigated which cell subsets become activated in this response. Mononuclear cells from 16 HTLV-seropositive former blood donors and 9 seronegative controls were cultured for 7 days; activation was then assessed by measuring DNA synthesis in cultured cells and by monitoring CD25 expression by CD3, CD4, CD8, CD19, and CD16 52 lymphocyte subsets. Of the 16 cultures of HTLV+ donor cells, 10 showed spontaneous proliferation (Prol+ group) and 6 did not (Prol - group). Cytofluorometric analysis revealed a significant increase in the fractions of CD8 cells and CD16 56 cells expressing CD25 for the Prol+ group, compared to the Prol- and control groups. Similarly, the fractions of CD25 cells expressing CD8 or CD16 56 were significantly increased in the Prol+ group. Although neither the fraction of CD4 cells expressing CD25 nor the fraction of CD25 cells expressing CD4 were increased for the Prol+ group, the modal fluorescence intensity value for CD25 expression by CD4 cells was increased, suggesting some CD4 cell activation occurred as well. Blastoid cells were, on average, 79% CD25+, whereas the sum of CD4+CD25+ (27%), CD8+CD25+ (30%), CD19+CD25+ (3%), and CD16 56+CD25+ (35%) subsets was 95%; the presence of 17%CD8+ CD16 56+ cells accounted for most of this discrepancy. These findings indicate that spontaneous lymphocyte proliferation in HTLV infection reflects preferential activation of CD8 and CD16 56 cell subsets, apparently including the minor CD8+ CD16 56+ subset. © 1991.