Serial determinations of platelet counts in mice by flow cytometry

Elucidation of the pathophysiological basis of platelet disorders in murine models requires a reliable method for the frequent determinations of plate let counts in individual mice. Here, we present a rapid, reproducible and a ccurate flow cytometric method for enumeration of platelets that involves f luorescent staining of platelets in whole blood with specific antibody and the addition of known numbers of fluorescent beads for standardization of t he sample volume. Analysis of platelets obtained by tail bleeding indicated that this sampling procedure did not activate platelets, and that only fiv e microliters of blood were required for platelet counting. Using this meth od, we followed platelet counts in mice infected with the relapsing fever s pirochete Borrelia turicatae for 26 days, and found that this bacterium ind uces thrombocytopenia, a common manifestation of human relapsing fever. The refore, this method can be used to follow the number and the activation sta te of circulating platelets from individual mice over extended periods of t ime and is applicable to a wide range of murine models of platelet disorder s.