Effect of leucocyte reduction on the potential alloimmunogenicity of leucocytes in fresh-frozen plasma products

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Abstract
Background and Objectives Adverse effects mediated by leucocytes in cellular blood products are widely recognized. There are few studies, however, concerning the effects of residual leucocytes in fresh‐frozen plasma (FFP). We examined the quantities and characteristics of leucocytes in FFP in order to investigate the potential leucocyte‐associated adverse effects of FFP transfusion, focusing on the risk of alloimmunization. Materials and Methods The quantity of leucocytes in FFP was estimated by using the Nageotte method and flow cytometry (FCM) analysis. The viability and subsets of leucocytes were determined by FCM using propidium iodide (PI) and fluorescein‐conjugated antibodies. To investigate alloimmunogenicity caused by the leucocytes in FFP, mixed lymphocyte cultures (MLC) were performed using fresh, allogeneic peripheral blood mononuclear cells (PBMCs) as responder cells and cell‐concentrated thawed FFP as a stimulator. We also studied the performance of leucocyte‐reduction filters with FFP products. Results The average number of leucocytes in a single unit of FFP, derived from 200 ml of whole blood, was 2·98 × 106 (range 0·99–8·38 × 106). The majority of these cells were PI‐positive dead cells; however, a small but consistent population of PI‐negative cells was present in these products. Both dead and live cells expressed human leucocyte antigen (HLA) class I antigens, and ≈ 38% of these cells expressed HLA class II antigens. The average number of viable CD3+ T cells in one unit of FFP was 2·36 × 104. Growth of the allogeneic PBMCs increased following stimulation with highly concentrated FFP. Use of leucocyte‐reduction filters significantly reduced the concentrations of both PI‐positive (dead) and PI‐negative (live) cells. The growth of allogeneic lymphocytes after stimulation with FFP was also completely suppressed by leucocyte filtration of FFP. Conclusion Transfusion of FFP is potentially alloimmunogenic owing to its residual leucocyte content. Leucocyte‐reduction filters appear to be effective in suppressing the alloimmunogenicity of FFP.