CNS inflammation in IL-12 p35–/– mice. Animals were sacrificed at day 28 after immunization, and spinal cord inflammation was assessed by hematoxylin and eosin staining. Magnification: ×100. (a) Nonimmunized WT control. (b) Immunized WT mouse. (c) Immunized IL-12 p35–/– mouse. (d) Immunized IL-12 p40–/– mouse.