Figure 3. Lung-resident Mks produce platelets.

(A) Mice were simultaneously given CFSE o.p. and anti-CD42c platelet-labeling antibody i.p. Lung-derived platelets were quantified as CFSE⁺CD42c^– platelets by flow cytometry in representative plots. SSC, side scatter. (B) Results showed that 2%–5% of total platelets were lung derived (n = 9–12 from 3 independent experiments), and when normalized to CFSE⁺ Mks (n = 5; results are representative of 2 independent experiments), a maximum of approximately 10% of the platelets were lung-resident, Mk-derived. (C) CFSE data were validated by biotin delivered o.p. and by quantification of streptavidin-binding platelets (Plts) (n = 4; results are representative of 2 independent experiments). (D) CFSE⁺ lung-derived and CFSE^– platelets were agonist stimulated, and platelet activation was quantified by flow cytometry for CD62P surface expression. Lung-derived platelets and BM-derived platelets responded similarly to thrombin and U46619 (n = 4 per group; results are representative of 2 independent experiments). (E) Isolated platelets from mice treated with CFSE o.p. were stimulated with PAM3CSK4 (PAM) (10, 50, or 100 μg/mL) or Tyrode’s or with loxoribine (Loxo) (250, 400, or 500 μg/mL) or 1:1 DMSO/H₂O, and CD62P surface expression was compared in either CFSE⁺ or CFSE^– platelets (n = 4 per group; results are representative of 2 independent experiments). Data indicate the mean ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001, by (D and E) multiple t tests with Holm-Šidák multiple-comparison correction.