Altered lymphocyte markers and blastogenic responses associated with 24 hour delay in processing of blood samples

Lymphocytes separated from fresh heparinized blood or from blood stored 24 h at room temperature were tested for E rosettes, EAC Rosettes, and blastogenic response to phytohemagglutinin. Compared to lymphocytes from fresh blood, lymphocytes from 24 h stored blood contained a lower percentage of E rosette-positive cells, a higher percentage of E rosette-negative EAC rosette-negative null cells, and manifested a decreased blastogenic response to phytohemagglutinin. Fewer viable mononuclear cells were recovered by Ficoll-Hypaque separation from stored blood than from fresh blood. These findings suggest that storage-related changes may occur in T cells which cause a selective loss of such cells during Ficoll-Hypaque separation. A delay in processing of blood samples may therefore yield results of lymphocyte marker and functional assays which give the false impression of a decrease in T cells and an increase in null cells.