Removal of T and B lymphocytes by in-line filtration: evaluation of the efficiency of a polyester filter type (Pall WBF-2) by flow cytometric counting

Background and Objectives The aim of this study was to investigate whether in‐line filtration, using a polyester filter for the preparation of red cell concentrates (RCC) and plasma (PL), leads to an altered proportion of T and B lymphocytes in the fraction of residual white blood cells (WBC). Materials and Methods The capacity of Pall WBF‐2 in‐line filters to reduce the numbers of T and B lymphocytes from red blood cell concentrates (RCC) and plasma (PL) of 22 donations was investigated by three‐colour flow cytometry (FC) using the Tritest‐Trucount kit. T and B lymphocytes were identified using monoclonal antibodies (mAbs) against CD3, CD19 and CD45, conjugated with fluorescein isothiocyanate, phycoerythrin or peridinin chlorophyll protein‐A, respectively. As the number of B cells was below the detection limit of the FC method, WBC of the respective blood components of healthy donors were concentrated 25‐fold by Percoll density‐gradient centrifugation. In this fraction the absolute numbers of T and B cells, as well as their ratio, were determined using the Attractor software, which provides a discrimination of rare cell counts from FC in relation to debris. Results The mean numbers, as well as minima and maxima of T and B lymphocytes per unit, were as follows. T cells in RCC: 4·51 × 103 (1·68 × 102−4·09 × 104) and in PL: 1·35 × 103 (2·21–1·78 × 104); B cells in RCC: 2·33 × 103 (7·10 × 101−9·15 × 103) and in PL: 2·33 × 102 (7·5 × 102−2·8 × 103). T cells were retained, on average, at a higher level than B cells: 3·01 times higher in RCC and 1·01 times higher in PL. Conclusion After filtration, the ratio of T and B lymphocytes changed in RCC (1·95 : 1) compared with unfiltered blood, where it was 5·83 : 1. In PL the ratio did not change notably compared to unfiltered blood. The results of this research show that cell concentration (using gradient centrifugation) in combination with an appropriate FC acquisition and analysis procedure, allows both residual T and B lymphocytes (being under the detection limit without cell concentration) to be determined.