Effects of platelet factor 4 on morphological and biochemical signs of apoptosis in T-lymphocytes
Platelet factor 4 (PF4) pertains to a family of CXC chemokines released by activated platelets. PF4 has a broad spectrum of effects on different cell types, including modulation of the immune response. In this study, we explore effects of PF4 on the morphological and biochemical signs of apoptosis in human T-lymphocytes in vitro. T-lymphocytes were isolated from peripheral blood of healthy donors using negative immunomagnetic separation and cultured in the complete RPMI 1640 medium for 24 hours in the absence and presence of PF4 added at a final concentration of 2 /ug/ml or 100 ug/ml. After 2, 4, 6, 12 and 24 hours of incubation the cells were studied with transmission electron microscopy and Western blot analysis with respect to potential apoptotic changes. The electron microscopy of control T-lymphocytes showed that the vast majority of the cells had a morphology characteristic of apoptosis at different stages. Adding PF4 at a concentration of 2 ug/ml reduced the number of cells at the late stages of apoptosis, while maintaining the signs of the early apoptosis in most of the T-lymphocytes. In the presence of 100 ug/ml PF4 nearly all of the cells kept a typical morphology of normal T-cells throughout the time of cultivation. The morphological apoptotic changes correlated well with expression of caspase-3, which was clearly detected in the control cells and cells treated with 2 ug/ ml PF4, but was almost abolished in the cells treated with 100 ug/ml PF4. Our results provide direct evidence for the dose-dependent anti-apoptotic effects of PF4 on T-cells, suggesting that PF4 sustains an immune response by extending T-lymphocyte survival.