Human immunodeficiency virus type 1 (HIV-1) selectively infects cells expressing the CD4 molecule, resulting in substantial quantitative and qualitative defects in CD4+ T lymphocyte function in patients with acquired immunodeficiency syndrome (AIDS). However, only a very small number of cells in the peripheral blood of HIV-1-infected individuals are expressing virus at any given time. Previous studies have demonstrated that in vitro infection of CD4+ T cells with HIV-1 results in downregulation of CD4 expression such that CD4 protein is no longer detectable on the surface of the infected cells. In the present study, highly purified subpopulations of peripheral blood mononuclear cells (PBMCs) from AIDS patients were obtained and purified by fluorescence-automated cell sorting. They were examined with the methodologies of virus isolation by limiting dilution analysis, in situ hybridization, immunofluorescence, and gene amplification. Within PBMCs, HIV-1 was expressed in vivo predominantly in the T cell subpopulation which, in contrast to the in vitro observations, continued to express CD4. The precursor frequency of these HIV-1-expressing cells was about 1/1000 CD4+ T cells. The CD4+ T cell population contained HIV-1 DNA in all HIV-1-infected individuals studied and the frequency in AIDS patients was at least 1/100 cells. This high level of infection may be the primary cause for the progressive decline in number and function of CD4+ T cells in patients with AIDS.

Using subtractive cDNA cloning we have isolated a series of cDNA clones that are exclusively or selectively expressed in B lymphocytes. mRNA transcripts from one such cDNA clone, referred to as BL11, were found to be expressed at low levels in RNA from normal B lymphocytes, but at very high levels in RNA from in vitro activated B lymphocytes. One major 2.5-kb BL11 mRNA transcript was detected, while low levels of 4.8- , 1.8-, and 1.6-kb transcripts were also found. BL11 mRNA transcripts were absent or present at low levels in RNA prepared from resting or mitogen activated T cells, a variety of lymphoid cell lines including several B-cell lines, and several different tissues. Low levels of BL11 transcripts were found in poly(A) RNA purified from brain and lung. A study of the kinetics of BL11 mRNA accumulation in B lymphocytes stimulated in vitro with Staphylococcus aureus Cowan strain I showed a rapid induction of BL11 mRNA within 2 hours of stimulation with peak expression by 16 hours and a mild decrease with time following the peak levels. Consistent with the in vitro data, in situ hybridization using antisense BL11 RNA probes and human tonsillar tissue localized BL11 transcripts in B-cell-enriched areas. Multiple BL11 cDNA and genomic clones were isolated and sequenced to complete and verify the BL11 cDNA sequence (2,404 bp). A 615-nucleotide open reading frame predicted to encode for a 205-amino acid protein with a molecular weight of 23 Kd was identified. Search of protein data bases with the predicted BL11 protein showed homologies to several members of the Ig superfamily. Analysis of the predicted protein showed a likely signal peptide, a single membrane spanning region, and one V-like Ig domain with three predicted n-glycosylation sites. Southern blot analysis of human genomic DNA suggested that BL11 is a single copy gene without evidence of rearrangement. Primer extension and S1 nuclease mapping identified four tightly clustered transcriptional start sites approximately 40 bp upstream of the predicted translation start site. The first 270 bp of the promoter region were sequenced and found to contain a CATAA box rather than a TATAA box and several DNA motifs found in activation genes. BL11 should prove to be an interesting gene that likely encodes for a protein involved in B-cell activation.

SUMMARYDendritic cells (DC) were purified from human peripheral blood using a rapid and simple method based on magnetic depletion of phagocytes with carbony! iron, followed by centrifugation of nonphagocytic cells on a Percoll density gradient and depletion of lymphocytes and macrophages/ monocytes with a panel of MoAbs and immunomagnetic beads. Enriched DC were obtained with >99'^. purity as judged by non-specific esterase (NSE) staining. After isolation, these cells, representing 0-4% of the starting mononuclear cell population, still function as potent antigenpresenting cells for purified T lymphocytes. The present results confirm the ability of human peripheral blood DC lo present soluble antigens to T cells including microbial antigens and show, furiher. that DC arc more potent soluble antigen-presenting cells than monocytes. The method was successfully applied to the purification of DC from the blood orHIV-infccted individuals. We could not detect decreased numbers of DC in four individuals with early HIV infection and no replicating HIV was detected by in situ hybridization in the DC.