Effect of IL-1 on expression of TGF-beta signaling proteins in cartilage. Knee joints of (a) young (5 months old) and (b) old (2 years old) mice were injected with IL-1 24 h prior to isolation of the knee joints. Paraffin sections of knee joints were stained immunohistochemically for TGF-beta1, TGF-beta2, TGF-beta3, TGF-beta receptor I (TGF-betaRI), TGF-betaRII, Smad2, Smad3, Smad4, Smad6, Smad7 and Smad-2P. Subsequently, the number of cells staining positive were scored with a computerized imaging system and corrected for the total number of cells. After IL-1 injection, Smad2 expression increased only in the medial tibial cartilage and TGF-beta1 and TGF-beta2 expression increased only in the lateral tibial cartilage. Error bars display the standard error. For statistical analysis, a Student's t-test was used. * = p < 0.05.