SummaryHigh levels of unintegrated viral DNA accumulate during human immunodeficiency virus type 1 (HIV 1) infection of CEM T cells. Reinfection of already infected cells is required to attain these levels and reinfection also promotes the development of HIV-induced cytopathology. Rates of virus production, however, are independent of the accumulation of unintegrated viral DNA . Neutralizing antibody added soon after infection reduced viral DNA levels without appreciably affecting the production of cell-free viral p24 antigen or reverse transcriptase activity. Only 50 pM AZT were required to reduce the accumulation of unintegrated viral DNA by 50% in contrast to the 25 nM required to inhibit virus production by 50%. Cytopathology,-as measured by number of syncytia in infected cell cultures, was correlated with highly elevated levels of unintegrated viral DNA . The minimal levels of unintegrated viral DNA present constitutively in the persistently infected HCEM cell line were consonant with the absence of cytopathic effects in these cells. These data demonstrate that inhibiting the reinfection of already infected cells modulates cytopathic HIV-1 infection to a form that is persistent and noncytopathic.Depletion of CD4 T lymphocytes is an important feature of the natural history of HIV-1 infection (1, 2). Reduced numbers in this cell population predict disease progression (1-3) and are likely to contribute to immunodeficiency (4) . HIV-1 infection in vitro is rytopathic for T lymphocytes (5-7) and T lymphoid cell lines (8,9). This cytopathology occurs by the formation of syncytia when infected and uninfected CD4+ cells are admixed (8, 9) and direct cell killing by a mechanism independent of cell fusion (10) . Based on the cytopathic effects of HIV-1 infection of T cells in vitro, this mechanism was proposed to be a crucial feature of viral pathogenesis in AIDS (6,5,11, 12) . In this study, we have examined the role of reinfection and viral DNA accumulation in cytopathic and persistent HIV-1 infection of the CEM cell line.Host-pathogen interactions leading to cytopathology have been characterized extensively in avian retrovirus models. The accumulation of high levels of unintegrated viral DNA is a recognized feature of rytopathic infection by these retroviruses (13, 14) and was also shown to be an important marker of pathogenesis in the case of feline leukemia virus infection of cats (15)
and equine infectious anemia virus infection of horses (16).Unintegrated viral DNA is generated by reverse transcription of infecting viral RNA . A linear viral DNA molecule 1035 flanked at both ends by long terminal repeat (LTR)t sequences (17) is generally found to be the most abundant form of unintegrated viral DNA . Intramolecular recombination between the LTR sequences then generates a circular molecule with one LTR that is of intermediate abundance . A circular DNA form with two LTR seems to arise via direct ligation of the ends of a linear molecule and is the least abundant species . Importantly, these DNA species are pro...