Flow cytometric analysis of residual leukocytes in filtered blood components.

Knowing the population of residual leukocytes in filtered blood products is as important as knowing the number of leukocytes to elucidate the mechanisms of the side effects caused by transfused leukocytes and to find ways to prevent them completely. We concentrated residual leukocytes in the filtered red cell concentrates (RCC) and platelet concentrates (PC) by centrifugation with Ficoll-Paque and Percoll respectively, and analyzed the differential population of leukocytes, as well as subpopulations and subsets of lymphocytes using a flowcytometer. Among leukobytes collected from the filtered PC, monocytes were found to be most effectively removed by all the filters tested in this study; the Pa11 PL100, Sepacell PL5N, Imugard PL and Imugard IG-400Y. When using filters made for the RCC, Imugard IG-400Y, Pall RC100, Sepacell R-500N, Imugard RC, monocytes are also most effectively removed. Granulocytes tended to come out of filters made of non-woven polyseter fibers (Sepacell R-500N and Pall RC100) if the RCC was fresh and filtered above 4°C. B cells were removed more effectively than T cells by filters made for RCC. On the other hand the specificity to the B cells of filters made for PC was much less than that observed using the filters made for RCC. CD8+ cells were more specifically removed by the filters made for PC. Among the RCC filters, the Imugard RC filter made of microporous polyvinyl alcohol could remove CD8+ cells most effectively. The filters made for RCC removed NK cells more effectively than T cells, but the filters made for PC did not show specificity to NK cells.This study should help to clarify the mechanisms of alloimmunization and viral infection transmitted by specific leukocytes and also to elucidate the mechanism of leukocyte-depletion by filters, which are not perfectly understand at present.