White blood cell subsets in buffy coat-derived platelet concentrates: The effect of pre- and poststorage filtration

Background and Objectives: Our objective was to study the effect of storage time on the filtration of platelet concentrates (PCs). We compared the tot al number of white blood cells (WBC), as well as the distribution of WBC su bsets, in units filtered before and after storage. Materials and Methods: B uffy coat-derived PCs were filtered either fresh or after 5 days of storage , and total WBC were enumerated by flow cytometry, WBC subsets were analyze d by flow cytometry with three-color fluorescence. Results: The total numbe r of white cells before filtration was significantly higher in fresh units compared with stored units, whereas in postfiltration samples the number of white cells was significantly lower in the fresh compared with the stored units. Although absolute numbers were significantly reduced, filtration als o induced significant changes in the proportions of subsets in both fresh a nd stored units; the percentage of T cells was decreased, whereas the perce ntage of B cells and monocytes was increased after filtration. Conclusion: Our results suggest that prestorage WBC filtration of platelet concentrates is superior in reducing the absolute numbers of WBC. However, both pre- an d poststorage WBC filtration significantly affect the proportions of WBC in the final product, decreasing the number of T cells while apparently incre asing the proportion of MHC class II-positive cell populations. Copyright ( C) 2000 S. Karger AG, Basel.