Infection with human immunodeficiency virus type 1 (HIV-1) results in a wide range of immunologic and hematopoietic abnormalities. The overall goal of this dissertation was directed toward obtaining a better understanding of the interactions of HIV-1 and myeloid cells in relation to the pathogenesis of AIDS. The human myelomonocytic cell line, HL-60, was used as a model system to determine if HIV-1 infects myeloid progenitor cells and subsequently, if infection affects their differentiation. HL-60 cells and the human prototypic T cell line, H9 were infected with three different HIV-l isolates (IIIB, PM213, and NL4-3) which are known to infect T cells. All three isolates productively infected both H9 and HL-60 cells; however, HIV-1 antigen expression and cytopathicity was delayed by approximately 15 days in infected HL-60 cells compared H9 cells. To examine the effect of HIV-l infection on myeloid differentiation, chronically infected HL-60 cells and clonal lines derived from them were induced to differentiate into either granulocytes by treatment with dimethyl formamide (DMF) or into monocytes by treatment with phorbol l2-myristate 13 acetate (PMA). By both cellular morphology and function, approximately the same percentage of treated, HIV-infected HL-60 cells differentiated into either granulocytes or monocytes as treated, control HL-60 cells. Taken together, these results indicate that HIV-1 infection does not affect the morphological or functional differentiation of HL-60 cells.
In an effort to understand the differences in the regulation of HIV-l infection in myeloid versus T cells, the life cycle of NL4-3 was examined in HL-60 cells and H9 cells. Initially, NL4-3 replication was restricted in HL-60 cells compared to H9 cells. This restriction was overcome 15 days after infection by the generation of a viral isolate, NL4-3(M). NL4-3(M), harvested during the lytic phase of NL4-3 infection of HL-60 cells, caused cell death approximately 8 days after infection in both H9 and HL-60 cells. Although measurements of viral entry kinetics demonstrated that the timing of entry of NL4-3 and NL4-3(M) in HL-60 cells and NL4-3 in H9 cells was similar, a quantitative polymerase chain reaction (PCR) analysis of newly reverse transcribed NL4-3 DNA in H9 and HL-60 cells revealed that NL4-3 infected H9 cells and NL4-3(M) infected HL-60 cells contain consistently higher amounts of newly reverse transcribed DNA than NL4-3 infected HL-60 cells. The delay in NL4-3 replication in HL-60 cells was further amplified by inefficient spread of the virus throughout the HL-60 culture as measured by RNA production and DNA integration suggesting that another step in the viral life cycle after reverse transcription was also restricted. These results suggest that the efficiency of NL43 replication in HL-60 cells is restricted at several steps in the viral life cycle. Further, these restrictions are overcome by the generation of a viral variant, NL4-3(M), which efficiently replicates in myeloid cells.
The tropism of NL4-3(M) was further characterized by testing its growth in monocyte-derived macrophages (MDM). Unlike NL4-3, NL4-3(M) productively infected MDM cultures. The ability of NL4-3(M) to infect macrophages was conferred by the envelope gene. This was demonstrated by the ability of the recombinant virus, NL4-3envA, which contains the envelope of NL4-3(M) in the context of the NL4-3 genome, to infect and replicate in MDM cultures. The envelope gene of NL4-3(M), however, did not confer ability to rapidly kill HL-60 cells. Together, these findings demonstrate that viral determinants controlling entry into MDM are different trom the determinants controlling the cytopathic phenotype in HL-60 cells
