OCP crystal-induced iNOS mRNA expression and NO release is not IL-1β dependent. Nonadherent articular chondrocytes were stimulated with OCP crystals or IL-1β for 24 hours with or without pretreatment with IL-1ra for 1 hour. (a,b) IL-1β and iNOS transcripts were assessed by RT-PCR and (c) NO release was measured in the supernatants. The RT-PCR was representative of three experiments. GAPDH, glyceraldehyde-3-phosphate dehydrogenase; IL-1ra, IL-1 receptor antagonist; iNOS, inducible nitric oxide synthase; NO, nitric oxide; OCP, octacalcium phosphate.