TLR7 is present in human and mouse platelets and TLR7 activation induces a reduction in platelet count. (A) TLR7 mRNA levels in human platelets from participants in the FHS (n = 1889, 839 men and 1050 women) screened by qPCR. (B) TLR7 protein levels in human platelets of 6 healthy donors (not involved in the FHS) screened by western-blot analysis (F, females; M, men). (C) TLR7 mRNA levels in murine platelets screened by qPCR (n = 5 males, n = 6 females). (D-G) WT (baseline platelet count 729 ± 167 × 10³ platelets/μL) and TLR7KO male mice (baseline platelet count 780 ± 147 × 10³ platelets/μL) at 14 weeks of age were injected (once) with TLR7 agonist, Loxo or at 17 weeks of age with EMCV. Percent of baseline platelet count in WT (D) and TLR7KO (E) mice injected with Loxo and WT (F) and TLR7KO (G) mice infected with EMCV. SEMs (H) and TEMs (I) of human platelets treated with EMCV. White circles in H encompass viral particles. Bar represents 2 μm in H and 0.2 μm in I. Data are average ± SD and were analyzed by Student t test using n = 5 animals/group (C-H).