CD4⁺CD8⁺ thymocytes are susceptible to DNA fragmentation induced by phorbol ester, calcium ionophore and anti‐CD3 antibody

Abstract

Abstract Stimulation of murine thymocytes with phorbol ester or calcium ionophore for 18–24 h resulted in 70%–80% fragmentation of DNA into 180–200‐bp multiples, followed by cell death. Experiments with fractionated subpopulations by panning or flow cytometry revealed that DNA fragmentation was selectively observed in CD4 + CD8 + cells and in a portion of CD4 − CD8 + cells. To investigate whether DNA cleavage is also inducible via antigen‐specific receptors, thymocytes were incubated in wells precoated with anti‐CD3 antibody. An approximately 20% increase of DNA fragmentation was constantly observed when unseparated thymocytes were stimulated with anti‐CD3 antibody. In this anti‐CD3‐induced DNA degradation, CD4 + CD8 + cells are probably the target cells, since (a) fetal thymocytes at day 18 of gestation were found vulnerable to anti‐CD3‐induced DNA cleavage and (b) flow cytometry analysis of viable cells recovered after cultivation in the anti‐CD3‐coated wells revealed that CD4 + CD8 + cells were preferentially decreased. Further experiments with purified CD4 + CD8 + cells, however, could not define a clear‐cut increase of DNA fragmentation when isolated CD4 + CD8 + cells were stimulated with anti‐CD3 antibody. Addition of interleukin (IL) 1, IL 2, IL 3, IL 4 or interferon‐γ to the CD4 + CD8 + cell cultures failed to yield a DNA cleavage similar to that of unseparated thymocytes.

Keywords

Affiliated Institutions

• Juntendo University JP
• Keio University JP

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