Normal human peripheral blood lymphocytes were tested for their susceptibility to infection with retroviruses isolated from patients with the acquired immunodeficiency syndrome (AIDS) or AIDS-related complex. Of 10 normal individuals tested, lymphocytes from all subjects became infected and produced virus as detected by assay for Mg+2-dependent reverse transcriptase. Lymphocytes from different individuals were demonstrated to be either high or low producers of reverse transcriptase after infection. The kinetics of virus production were similar in cells from both high- and low-producing individuals. A significant correlation was observed between high and low viral-producing lymphocytes and expression of the Leu-3/T4 (CD4) surface molecule. Mitogen-stimulated peripheral blood lymphocytes exposed to HTLV-III/LAV manifested productive viral infection, as reflected by the appearance of early syncytia, followed by reverse transcriptase. Unstimulated peripheral blood lymphocyte cultures displayed late syncytia but no detectable reverse transcriptase upon exposure to virus. The addition of anti-human interferon-alpha did not appear to have an appreciable effect on viral production in normal peripheral blood lymphocytes exposed to the virus.
Cross-priming is a critical component of T cell responses to cancers and viruses, and involves transfer of antigen from antigen donor cells to the antigen presenting cells. In spite of the centrality of antigen in this process, the influence of the quantity of antigen expressed by the antigen donor cell on the efficiency of cross-priming remains un-examined. Here, we have created a novel system where the model antigen ovalbumin is expressed in P815 (d haplotype) cells under the control of an inducible promoter. However, even in un-induced condition, a very low level of ovalbumin can be detected using highly sensitive methods. We have used titrated quantities of un-induced and induced cells, expressing vastly different quantities of ovalbumin, and have monitored cross-priming of the endogenous anti-SIINFEKL T cell response quantitatively, using in vivo cytolytic T lymphocytes assays. The experiments show, paradoxically, that minute quantities of antigen expressed by a large number of cells are far more effective at cross-priming than exponentially larger quantities of antigen expressed by fewer cells. The results point to the existence of cell-associated factors that enhance the availability of antigen in the antigen donor cells to the antigen presenting cells by orders of magnitude.
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