Repeated intraperitoneal injection of mice is a model for sustained ITP. (A) A single intraperitoneal injection of anti-CD41 antibody (delineated by an arrow) every 48 hours induces severe thrombocytopenia associated with an increase in mean platelet volume (MPV). For routine monitoring of ITP induction, mice were bled 24 hours after injection (n = 5-10 mice). P values were calculated by a two-way analysis of variance (ANOVA) with Sidak’s multiple comparison test (****P < .0001, MPV 1 day post injection control vs ITP ***P = .0009, MPV 21 days post injection control vs ITP ***P = .0003). (B) Circulating TPO levels during ITP progression (n = 4-5 mice; data are representative of 2 independent experiments). P values were calculated by a Kruskal-Wallis test with Dunn’s multiple comparisons test (control vs 2-week ITP P > .99, control vs 4-week ITP P > .99, 2-week ITP vs 4-week ITP P > .99). (Ci) BM megakaryocyte (Mk) numbers during ITP progression (n = 5-8 mice; data are representative of 2 independent experiments). P values were calculated by a Kruskal-Wallis test with Dunn’s multiple comparisons test (control vs 2-week ITP P > .99, control vs 4-week ITP **P = .0069, 2-week ITP vs 4-week ITP P = .10). (Cii) Representative hematoxylin and eosin stained diaphysis BM sections from WT femurs with Mks indicated by yellow stars. Images were obtained using a Zeiss AxioScan.Z1 slide scanner. (D) Gene Ontology terms within the biological process domain and reactome pathways identified by STRING analysis of upregulated cytokines in the BM (i) and plasma (ii) of mice with 4-week ITP relative to control. Cytokine analysis was performed using a Proteome Profiler Mouse XL Cytokine Array Kit (R&D Systems). Data are shown as mean ± standard deviation (SD). Red dotted lines,log10(0.05)=1.3; EPH, Erythropoietin producing hepatocellular carcinoma receptors; Ephrin=EPH receptors interacting proteins; IL-1, interleukin-1.