ELIMINATION OF MONOCYTES FROM CULTURES ACTIVATED WITH RECALL ANTIGENS

Recent data provide evidence that antigen-specific CD4(+) T-cell clone s or antigen-activated T-cell lines can kill antigen-presenting cells (APC). We focused our studies on monocytes acting as APC in cultures o f T cells freshly isolated from peripheral blood. The presence of mono cytes in culture was monitored by their ability to emit light during p hagocytosis of latex particles (latex-induced chemiluminescence). Usin g this approach as well as flow cytometry, evidence is presented that monocytes are eliminated from cultures with T cells activated with rec all antigens (PPD or TT). The mechanism of monocyte elimination involv ed apoptosis as judged from in situ detection of DNA strand breaks by the terminal deoxynucleotidyl transferase assay. The antigen- but not lectin-dependent monocyte elimination was MHC-restricted and mediated by CD4(+) T lymphocytes. This finding supports the hypothesis that eli mination of APC is a general phenomenon during T-cell activation and m ay represent an important immunoregulatory mechanism.