Macrophages stain positive for IL-1β and MIP-1α in the joints of nonimmunized E/P-selectin mutant mice. Immunohistochemistry for IL-1β and MIP-1α in synovial tissue of E/P-selectin mutant CIA mice. Staining for both cytokines showed clear immunopositivity on macrophages (arrows), whereas ST endothelial cells (arrowheads) remained negative. Original magnification: 400×. CIA, collagen-immunized arthritis; MIP, macrophage inflammatory protein; wt, wild-type.