siFXIIIB decreased FXIII-B mRNA in the livers of mice, leading to a sustained decrease of FXIII-A protein in plasma but not platelets for more than 3 weeks. Mice were injected with a single dose of siFXIIIB (green) or siLuc (lavender). (A) mRNA encoding FXIII-B was measured in liver tissue using quantitative polymerase chain reaction normalized against a housekeeping gene Ppia and graphed relative to FXIII-B mRNA from untreated mice. (B) Representative western blots against FXIII-A, in which each lane contains the plasma from an individual mouse in either treatment group. The triangular marker indicates the expected molecular weight of FXIII-A (83 kDa). (C) Quantification of panel B using densitometry, normalized to a loading control, and graphed relative to FXIII-A antigen from untreated control mice; n = 3 mice per time point. (D) Representative western blot against FXIII-A in PPP and washed platelets from mice treated with siFXIIIB 14 days previously. The quantification is normalized to loading controls platelet factor 4 (platelets) or immunoglobulin G (plasma) and relative to untreated control. (E) Plasma FXIII-A quantified at various time points after repeated injections of siFXIIIB relative to starting concentrations before treatment; n = 3 mice per time point; vertical gray dashed lines indicate times of injections. For all graphs, values represent mean ± standard error of the mean (SEM). ns, not significant (P > .05); *P < .05; **P < .01.