Irradiation of platelet components: inhibition of lymphocyte proliferationassessed by limiting-dilution analysis

BACKGROUND: Using a limiting-dilution analysis (LDA) assay that measures cl onigenic T cells, it has been demonstrated that, with 2500 cGy, there is no T-cell growth in red cell components irradiated in blood bags. In the curr ent study, the LDA assay was used to investigate the effect of gamma radiat ion on the proliferative capacity of T cells in plateletpheresis components . STUDY DESIGN AND METHODS: Platelets were collected by using an apheresis in strument and settings that provided sufficient mononuclear cells for the LD A assay. Platelet components (n = 8) were irradiated in I-L plastic bags 24 hours after collection with 500, 1500, and 2500 cGy of gamma radiation in a stepwise manner. Mononuclear cells were isolated after each irradiation d ose by the use of ficoll-hypaque. A density separation medium was used to r educe the platelet numbers. T cells were enumerated by fluorescence-activat ed cell sorter and functionally assessed by LDA assay, which quantified T c ells proliferating in the presence of polyclonal stimuli and cytokines. The frequency of T-cell growth (f) was visually scored after 4 weeks of incuba tion at 37 degrees C. Data were calculated as f(experimental)/f(control) an d expressed as log(10) reduction. RESULTS: The T-cell content of the mononuclear cell population was 17 +/- 1 0.5 percent, which was unaltered by irradiation. After 500-cGy irradiation, functional T cells were reduced by 2.09 log(10). Irradiation with 1500 cGy resulted in a 3.96 log(10) reduction, but viable clonable T cells were det ected in all experiments. With 2500-cGy irradiation, no T-cell growth was d etected; this represented a greater than 4.86 log(10) reduction. RESULTS: The T-cell content of the mononuclear cell population was 17 +/- 1 0.5 percent, which was unaltered by irradiation. After 500-cGy irradiation, functional T cells were reduced by 2.09 log(10). Irradiation with 1500 cGy resulted in a 3.96 log(10) reduction, but viable clonable T cells were det ected in all experiments. With 2500-cGy irradiation, no T-cell growth was d etected; this represented a greater than 4.86 log(10) reduction. CONCLUSION: As the dose of gamma radiation delivered to plateletpheresis co mponents increased, the number of residual functional T cells decreased exp onentially. irradiation with 2500 cGy inactivates T cells in apheresis plat elets, as measured by an LDA assay.