Figure 5
Phagocytosis of SCs and GERCs without migration. (a) qRT-PCR analysis of macrophage markers (F4/80, Mac-1, and Iba1) and M1 markers (Il1b, Il6, and interleukin 12b (Il12b)) after LPS treatment (time point, 9 h; *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001, t-test; 0 ng/ml: n = 4, 100 ng/ml: n = 4, 0 ng/ml: n = 6, 1000 ng/ml: n = 4 for Il12b; 0 ng/ml: n = 4, 100 ng/ml: n = 4, 0 ng/ml: n = 4, 1000 ng/ml: n = 4 for the other genes). LPS-induced macrophage marker expression indicates that LPS stimulates SCs and GERCs as cochlea-resident macrophages. (b) qRT-PCR analysis of macrophage markers (F4/80, Mac-1, and Iba1) and M1 markers (Il1b, Il6, and Il12b) after poly I:C treatment (time point, 9 h; *P < 0.05, **P < 0.01, t-test; 0 µg/ml: n = 4, 20 µg/ml: n = 4, 0 µg/ml: n = 5, 200 µg/ml: n = 4 for F4/80; 0 µg/ml: n = 4, 20 µg/ml: n = 4, 0 µg/ml: n = 3, 200 µg/ml: n = 4 for the other genes). Poly I:C upregulated macrophage marker expression, indicating that poly I:C also activates SCs and GERCs as cochlea-resident macrophages. (c) SC phagocytosis was observed during LPS treatment. (d) Sets of immunostained whole mounts and sections showing EGFP-E. coli in the SCs (white arrowheads) during EGFP-E. coli infection. The lower right image of SCs also shows green signals in these cells, indicating SC phagocytosis of the bacteria. (e) The confirmation of SC phagocytosis of EGFP-E. coli using cryosections from the cochlear sensory epithelium after EGFP-E. coli infection. SC cryosections after EGFP-E. coli infection showing EGFP signals inside (arrowheads) and outside (arrows) the SCs. EGFP signals inside the SCs indicate phagocytosis of E. coli by the SCs, while EGFP signals outside the SCs indicate E. coli attachment to the SC surfaces. These findings show that SCs undergo phagocytosis during viral and bacterial infections, which strongly supports a role for SCs in mounting an innate immune response against microbes as macrophages. Scale bars, 20 µm. Error bars, standard errors.
