K4-cKO mice are susceptible to bacterial infection but resistant to EAE. (A) K4-cKO mice exhibited higher mortality rate than the Cre group after E coli intraperitoneal injection. n = 12 in each group. (B) Bacteria burden in the blood and peritoneal fluid harvested 14 hours postinjection. (C) TNF-α levels in serum at 4 hours postinjection. K4-cKO mice showed delayed occurrence and less disease severity after EAE induction, demonstrated by clinical score (D) and weight loss (E). n = 14 in each group. Difference was determined by 2-way ANOVA. For panel D, interaction P < .0001. For panel E, interaction P < .0021. For both panels D and E: time, P < .0001; genotype, P < .0001. (F) Spinal cord from lumbar 1 to 3 were taken from Cre and K4-cKO mice at disease peak (day 28) of EAE. Fluorescent myelin staining showed less demyelination in K4-cKO group. Hematoxylin and eosin (H&E) staining confirmed the cell infiltration in the foci. Representative data from 3 independent experiments. Original magnification ×200 (taken with a Nikon microscope; 20× objective, 10× eyepiece lens). (G) Immune cell infiltration in spinal cord as measured by flow cytometry at initiation of EAE (day 14). Neutrophils (CD45⁺CD11b⁺CD11c⁻Ly6G⁺), Th cells (CD3⁺CD4⁺), B cells (CD19⁺CD3⁻), and DCs (CD45⁺CD11b⁺CD11c⁺Ly6G⁻) were shown. n = 13 in each group. P < .05 was considered significant.