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


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.


CONCLUSIONS
The CD4/CD8 ratio affects the apoptotic response of human lymphocytes and CD4(+) T-cells.
Health Canada, Consumer and Clinical Radiation Protection Bureau, 775 Brookfield Road, Postal Locator 6303B, Ottawa, Ontario, K1A 1C1, Canada. Ruth_Wilkins@hc-sc.gc.ca
R C
RC
Wilkins
B C
BC
Kutzner
M
M
Truong
J R N
JR
McLean
D000328:Adult; D017304:Annexin A5 / Q000494:pharmacology; D017209:Apoptosis; D015496:CD4-Positive T-Lymphocytes / Q000473:pathology* / Q000528:radiation effects; D018414:CD8-Positive T-Lymphocytes / Q000473:pathology* / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D008297:Male; D008875:Middle Aged; D012542:Scattering, Radiation; D013997:Time Factors
D017304:Annexin A5