The Significance of Platelets with Increased RNA Content (Reticulated Platelets) A Measure of the Rate of Thrombopoiesis

Abstract

Direct flow cytometric measurement of nucleic acid content in individual platelets is possible using the fluorescent dye Thiazole Orange (Becton-Dickinson, San Jose, CA). When applied to studies of thrombocytopenic patients, platelets with elevated nucleic acid content ("reticulated platelets") can be identified and quantitated. Labeling of these platelets is saturable and is abolished by treatment with RNAse. It has been suggested that, similar to the erythrocyte reticulocyte response to anemia, the number of these platelets appearing in the circulation may provide an estimate of the rate of thrombopoiesis. The authors studied 229 thrombocytopenic patients, measuring both reticulated platelets and platelet-associated immunoglobulin. The results show that for the subset of patients with normal levels of platelet-associated immunoglobulin, the average absolute number of reticulated platelets is independent of platelet count and remains in the normal range. For those with elevated levels of platelet-associated immunoglobulin, the absolute number of reticulated platelets increases in patients who are moderately thrombocytopenic (60 to 100 x 10(9)/L) but decreases to normal or subnormal levels as thrombocytopenia worsens. The latter finding has been duplicated in studies of mice made thrombocytopenic by injection of anti-platelet antiserum. These results are consistent with the hypothesis that reticulated platelets are subject to peripheral destruction at the same rate as mature platelets, and that in the severely thrombocytopenic patient their level may decrease despite an appropriate marrow thrombopoietic response.

Rapid platelet turnover in WASP(−) mice correlates with increased ex vivo phagocytosis of opsonized WASP(−) platelets

“…Reticulated platelets were simultaneously counted via the method of Ault et al [34], with gating as shown in Figure 5C. Figure 1B shows that while the mean percentage of reticulated platelets (RP) is not elevated in WASP(−) mice, our colony contained a subpopulation of mice for which this parameter was elevated (p = 0.016, Student's one-tailed t-test for proportion of platelets with >8% reticulated forms).…”

Reticulated platelets: analytical aspects and clinical utility

“…For long it has been thought that this RNA was a vestigial remnant of megakaryocytic RNA, but there are recent indications that platelets are able using this RNA for protein synthesis [9]. Anyway, they represent the youngest platelets in the circulation and are named reticulated platelets (retPLT), in analogy with reticulocytes in erythropoiesis [10]. The concentration of retPLT in bone marrow is on the average 2-3 times higher than in peripheral blood, where they correlate with megakaryocyte numbers [11].…”

Autoimmune Thrombocytopenia

“…RP can be detected with thiazole orange (TO; Lee et al, 1986) staining combined with flow cytometric analysis of the fluorescence (FL; Kienast & Schmitz, 1990). The TO labelling has been shown to be sensitive to ribonuclease (RNAase), and thus may be considered to be due to an increased RNA content (Ault et al, 1992). …”

“…Quantification of newly formed platelets would be useful and more easily adapted for clinical purposes and thus have advantages over platelet survival studies. In the circulation platelets with a high nucleic acid content, reticulated platelets (RP), have been thought to represent young platelets, and thus measurement of RP may give an estimate of megakaryocyte stimulation and platelet production (Ingram & Coopersmith, 1969;Kienast & Schmitz, 1990;Ault et al, 1992;Richards & Baglin, 1995).…”