The effect of the ratio of CD4+ to CD8+ T-cells on radiation-induced apoptosis in human lymphocyte subpopulations.

PURPOSE

Apoptosis occurs spontaneously in cultured human peripheral blood lymphocytes but is enhanced by exposure to ionizing radiation. Subpopulations of lymphocytes are known to have varying radiosensitivities to radiation-induced apoptosis. The purpose of this study was to examine the radiation-induced apoptotic response of CD4(+) and CD8(+) T-cells incubated as a complete lymphocyte population.

MATERIALS AND METHODS

Using a four-colour flow-cytometry method, which measures annexin-V binding to phosphatidyl serine and propidium iodide, spontaneous and radiation-induced apoptosis was measured in the total lymphocyte fraction and in CD4(+) and CD8(+) T-cell subpopulations.

RESULTS

It was found that CD8(+) T-cells were more sensitive to radiation-induced apoptosis than CD4(+) T-cells at doses up to 2 Gy. The yield of radiation-induced apoptosis in the total lymphocyte fraction decreased with increasing ratios of CD4(+) to CD8(+) T-cells (CD4/CD8 ratio). By manipulating the CD4/CD8 ratio within lymphocyte cultures, it was found that the CD4/CD8 ratio had a dramatic effect on the yield of spontaneous apoptosis of total lymphocytes fraction and CD4(+) T-cells but not CD8(+) T-cells.

CONCLUSION

The CD4/CD8 ratio affects the apoptotic response of human lymphocytes and CD4(+) T-cells.