Myeloid precursor cells expand in the blood before clinical episodes of EAE and are contained within the CD11b⁺Ly-6C^hi population. (A) SJL mice were immunized with PLP_139-151 in CFA. Mice were bled at various time points during relapsing-remitting EAE, and peripheral blood leukocytes were plated in methylcellulose cultures supplemented with GM-CSF and stem cell factor. GM-CFUs were counted on day 7. The data shown represent the mean (± SD) of 3 similar experiments. The frequency of GM-CFU at each time point represents the mean of at least 3 mice/group (*P < .05 comparing the frequency of GM-CFU before onset of EAE with their frequency during disease). (B) C57/B6 mice were immunized with MOG/CFA. Six days later, peripheral blood cells were stained for CD11b and Ly-6C and sorted into Ly-6C^hi, Ly-6C^int, and Ly-6⁻ subsets. (C) Sorted cells were plated in methylcellulose cultures as described in panel A, and GM-CFUs were counted on day 7. The data represent mean (± SE) of five experiments. (D) Hematoxylin and eosin staining of sorted CD11b⁺Ly-6C^hi cells. (E) CD115, CD62L, and Ly6G levels were measured on gated CD11b⁺Ly-6C^hi cells by flow cytometric analysis. Broken lines represent isotype controls. (B-E) Data are representative of at least 2 experiments.