Erythrocytes modulate the baseline frequency of sister-chromatid exchanges and the kinetics of lymphocyte division in culture

Abstract

The baseline sister-chromatid exchange (SCE) frequencies of human plasma lymphocyte cultures (PLC), but not pig PLC, were nearly twice as high as those of whole-blood cultures (WBC). Addition of human red blood cells (RBCs) to human PLC decreased the SCE frequency in proportion to the RBC-leukocyte co-incubation interval. When the period of RBC-leukocyte co-incubation was equivalent to the total length of the culture period (72 h), the SCE frequency was similar to that observed in WBC. Shorter co-incubation periods yielded SCE frequencies intermediate between those of PLC and WBC. Regardless of the species, cell proliferation was slower in PLC than in WBC. Experiments where RBCs were added to PLC showed that the time sequence of RBC incorporation also affects the cell-cycle progression of human and pig lymphocytes. When either human or pig RBCs were added immediately after PLC stimulation, the cell-cycle kinetics was similar to that of WBC. Shorter co-incubation periods made cell-cycle progression intermediate between PLC and WBC values. Thus, PBCs modulate the baseline frequency of SCEs in human PLC and the cell-cycle progression of both human and pig lymphocytes in a time-dependent manner. Two possible hypotheses for the heightened frequency of SCEs of human lymphocytes in RBC-free cultures were assessed. The loss of RBC-to-lymphocyte cellular contact in PLC did not influence the SCE frequencies of lymphocytes. Finally, the increase of SCEs in human PLC could not be related to differences in the generation time of lymphocytes in culture.