Background and Objectives: Leukocytes remaining in platelet concentrates may be responsible for side effects caused by platelet transfusion. A simple method of high sensitivity for determining trace numbers of leukocytes is currently needed. Materials and Methods: An automated leukocyte counter, the LD-1000, the principle of which is a combination of spinning down on the observation field of stained nuclei derived from a 100 μl neat sample and image digitization with a charge coupled device camera, was newly developed and tested for sensitivity and reproducibility. Results: While the theoretical lower limit of detection was 0.01 cells/μl, the limit of detection of the LD-1000 was verified to be 0.2 cells/μl. A good correlation (r = 0.86) was observed between the results obtained using the Nageotte method and the LD-1000. Repeated measurements also confirmed satisfactory reproducibility. Conclusions: The instrument provides a new method of enumerating residual leukocytes in platelet products with better sensitivity and easier procedure compared to the Nageotte method and will be useful for quality assurance purposes at blood centers.
Platelet donors sometimes show an increased platelet count following apheresis. We analyzed the effect of plasma obtained from such donors, along with thrombopoietin (Tpo), for growth and differentiation-inducing activity on a megakaryoblastic leukemia cell line, Meg-J. Colony formation was stimulated by donor plasma for Meg-J cells in a dose-dependent manner, and the time course of the sampling peaked 1 day after apheresis. Neither the donor plasma nor Tpo induced morphological differentiation. Donor plasma from any sampling time decreased CD41 and CD42b expression by more than 10%, and more than a 10% decrease of CD41 was induced by Tpo. The measurement of plasma Tpo showed no statistically significant increase after platelet donation. Our data suggest that, following apheresis, donor plasma contains factor(s) that: (a) stimulate growth rather than induce differentiation of a megakaryoblastic cell line; (b) are present in increased levels after apheresis; and (c) are different from Tpo.
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