Figure 6
Irf5 is involved in differentiation of the SCs into macrophages via Cd200r1 downregulation during virus infection. (a) In Irf5 KO mice, GERCs, but not SCs, migrated during the viral infection. (b) qRT-PCR analysis of F4/80, Mac-1, Iba1, Cd200, and Cd200r1 (*P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001, t-test, Irf5 KO Mock 9 h: n = 4, Irf5 KO TMEV 9 h: n = 5, Irf5 KO Mock 16 h: n = 4, Irf5 KO TMEV 16 h: n = 4). Compared with WT mice during the virus infections, F4/80 transcripts were fewer in the Irf5 KO mice, Cd200r1 transcripts were more in the Irf5 KO mice, whereas Cd200 transcripts in Irf5 KO mice induced by the virus infection were similar to the levels in the WT mice. These findings show that Irf5 activates macrophages by regulating F4/80 expression through Cd200r1 inhibition. Mac-1 expression in Irf5 KO mice did not increase during virus infection compared with WT mice, but Iba1 expression in Irf5 KO mice was upregulated by virus infection to almost the same level as in the WT mice. This indicates that Iba1-positive cells are not regulated by Irf5. (c) F4/80 expression in Irf5 KO mice increased in the GERCs but not in the SCs following virus infection, indicating that Irf5 regulates SC but not GERC differentiation into macrophages. (d) Scheme showing the intra- and inter-cellular signalling pathways involved in SC differentiation into macrophages. (e) Compared with WT samples where the SC area is mainly infected with TMEV (dsRNA positive), Irf5 KO samples show strong signal intensity of dsRNA over a broad area including the GER during virus infection. (f) There is no statistical difference in numbers of cells between WT (n = 3) and Irf5 KO (n = 3) shown in (e) (P = 0.10412149, t-test). (g) Irf5 KO samples (n = 3) show a significant increase in dsRNA signal intensity compared with WT samples (n = 3) (*P < 0.01, t-test), indicating the lack of SC conversion to macrophages accelerated virus infection in the cochlea. Scale bars, 20 µm. Error bars, standard errors.
