CELLULAR IMMUNOLOGY 125,1- 13( 1990) Characterization of Human B Cell (DK) and Promonocyte (U937) Clones after HIV-1 Exposure: Accumulation of Viral Reverse Transcriptase Activity in Cells and Early Syncytia Induction against SupTl Cells YOSHITATSUSEI,*'~-MASAHIRO~NOUE,$ M. MITSUOYOKOYAMA,$ J. GEORGE BEKESI,? AND PRINCE K. ARORA* *Laboratory ofNeuroscience, National Institutes of Health, Bethesda, Maryland 20892; TDepartment of Neoplastic Diseases, Mount Sinai School of Medicine, New York, New York 10029; and *Department qfImmuno1og.v. Kurume University School qfMedicine, Fukuoka, 830, Japan Received December 20, 1988; accepted August 27, I989 The kinetics ofHIV-1 infection were compared among human B (DK), promonocyte (U937), T-B hybrid (CEMX 174), and T (H9) cell lines. Just like H9 cells, CEMX 174 cells exhibited strong syncytia induction capacity against highly HIV- 1-sensitive CD4+ T cells (SupT 1) and had high reverse transcriptase (RT) release in the supernatant. DK and U937 cells showed syncytia induction capacity by 72 hr, but RT activity in the culture supernatant (extracellular RT) in- creased much later. RT activity in cell lysates (intracellular RT) became detectable at 12- 15 days. The inverted extracellular/intracellu~ar RT ratio and syncytia induction capacity were also observed in chronically infected DK (DK-BIB) and U937 (U937-BIB) cell lines and subclones from U937-BIB. Further, the coculture of H9 with DK-BIB (which indicates no detectable ex- tracellular RT release) showed remarkable amplification of extracellular RT with significant increase of T-B double marker hybrids (H9-DK-BIB). Our results suggest that B cells and/or monocytes/macrophages may acquire fusing capacity against CD4+ T cells in early stages of the infection and that these cell-to-cell interactions may also lead to a reduction in the number of CD4+ T cells. Further, these T-B and T monocyte hybrids may serve as temporal sites for viral replication. These in vitro studies may provide clues to the possible immunopathological roles of HIV-l-infected B cells and monocytes/macrophages and may help in understanding the mechanisms of viral burden on an infected host. o 1990 Academic PRESS, IX. INTRODUCTION HIV- 1, the etiologic agent of the acquired immune deficiency syndrome (AIDS)’ ( l-4), has a selective tropism for CD4+ T cells and produces characteristic cytopathic effects resulting in progressive depletion of CD4+ T cells (5-8). Syncytium formation, a specific cytopathic effect of HIV- 1, is mediated, at least in part, by an interaction of HIV- 1 gp 120-expressing cells with neighboring CD4+ cells. Syncytium formation can be inhibited by CD4 mAb treatment (9, 10) and by immunoprecipitation studies ‘Abbreviations used: HIV- 1, human immunodeficiency virus; AIDS, acquired immunodeficiency syn- drome; EBV, Epstein-Barr virus; RT, reverse transcriptase; iRT, intracellular RT; eRT, extracellular RT, mAb, monoclonal antibody; PBS, phosphate-buffered saline; FCS, fetal calf serum; DTT, dithiothreitol; TCA, trichloroacetic acid; FITC, fluorescein isothiocyanate; PE, phycoerythrin. ooos-8749/90$3.00 Copyright 0 1990 by Academic Press, Inc. All nghtsofreprcduction in any form reserved.