Adoptive transfer of IL-1–competent neutrophils and monocytes to Il-1β^−/− mice induces mobilization of host-derived effector cells into the spinal cord and restores EAE development. (A–C) Immunofluorescence confocal microscopy of spinal cord tissue sections from immunized Il-1β^−/− recipient mice 1 d after the transfer (i.e., at 11 dpi) of Gr1⁺ neutrophils and monocytes isolated from the bone marrow of IL-1β–competent LysM-GFP knock-in (A and B) or pIl1b-DsRed (C) mice. The insets in B are the zoomed-in images of the region delineated with dotted line in B. (D) Immunohistochemical colocalization experiments performed on tissue obtained at 1 d after transfer revealed that host-derived (GFP⁻) CD11b⁺ myeloid cells (red) infiltrated IL-1R1⁺ vessels (white) where Gr1⁺ GFP⁺ (green) cells were also present. (E) Clinical course of adoptively transferred EAE into MOG_35–55–immunized IL-1β KO (n = 15–16/group; data represent two pooled experiments). EAE was scored daily in WT → KO (IL-1β KO recipient mice with neutrophils/monocytes from WT donors) and KO → KO (IL-1β KO recipients with neutrophils/monocytes from IL-1β KO donors) mice up to day 7 after transfer (i.e., 17 dpi). The arrow indicates the time of adoptive transfer of neutrophils/monocytes. (F) Pie charts representing the percentage of animals that displayed hind limb paralysis among mice that developed EAE (n = 9/group). (G) Quantification of the number of CD11b⁺ myeloid cell foci in the spinal cord of WT → KO and KO → KO mice at 7 d after transfer (n = 9–10/group). The data are expressed as mean ± SEM. *, P < 0.05; **, P < 0.01 (E–G). Statistical analysis was performed using a two-way repeated-measures ANOVA followed by a Bonferroni post-hoc test (E) or a Student’s t test (F). Bars: (A–D) 25 µm; (insets in B) 10 µm.