Encephalitogenic Th17 cells enter supraspinal parts of the CNS but fail to migrate into the spinal cord when α4 integrins are blocked. (A) Naive T cells from 2D2 mice were differentiated into Th17 cells in vitro and transferred into Rag1^−/− mice, which were treated with control rIgG or blocking antibodies to α4 integrin (see Fig. 2). At the peak of disease, the CNS was prepared and dissected into brain (brain stem, cerebellum, and cerebrum) and spinal cord. Mononuclear cells were isolated separately and analyzed by flow cytometry. Numbers indicate percentages of CD3⁺CD4⁺ T cells within the live mononuclear cell compartment. Shown are representatives of five independent experiments. (B) Quantification of absolute numbers of CD3⁺CD4⁺ T cells infiltrating brain or spinal cord under treatment with control rIgG or antibodies to α4 (mean + SD, n = 4).