Infection of the human monocytic cell line Mono Mac6 with human immunodeficiency virus types 1 and 2 results in long-term production of virus variants with increased cytopathogenicity for CD4+ T cells.

The recently established human monocytic cell line Mono Mac6 expressing distinct characteristics of mature monocytes/macrophages was tested for its susceptibility to infection with human immunodeficiency virus. Inoculation of the cells with the T-cell-tropic human immunodeficiency virus strains human T-lymphotropic virus type IIIB and lymphadenopathy-associated virus type 2 led to a noncytopathic productive infection becoming apparent only after a latency period of up to 56 days. The infectibility of the Mono Mac6 cells was dependent on low levels of CD4 expression, as demonstrated by blocking experiments with various CD4-specific antibodies. Increasing with time after infection (greater than 200 days), the cultured Mono Mac6 cells released virus variants which showed shortened latency periods when passaged onto uninfected Mono Mac6 cells. Also, cytopathogenicity for several CD4+ T cells of the Mono Mac6-derived virus was drastically increased; thus, the infection of the H9 cell line with low doses of virus (less than 0.1 50% tissue culture infective dose per cell) led to giant syncytium formation within 1 day and subsequent death of all fused cells. We propose Mono Mac6 cells as a new model for the study of human immunodeficiency virus infecting the monocyte/macrophage lineage, particularly with regard to virus-host cell interaction and the influence of cell differentiation and activation on latency and development of virulence. The human immunodeficiency virus-infected Mono Mac6 cell may also serve as a valuable tool for in vitro testing of antiviral therapies.