Induction of synthesis and release of interleukin-8 from human articular chondrocytes and cartilage explants.

OBJECTIVE: The activation of neutrophils in the joint space may contribute to the destruction of cartilage matrix observed in rheumatoid arthritis. The capacity of articular chondrocytes to synthesize and secrete interleukin-8 (IL-8) and GRO alpha, two potent neutrophil chemoattractant peptides, was investigated to determine whether cartilage itself could serve as a source of these small cytokines.
METHODS: Induction of IL-8 and GRO protein was studied both at the messenger RNA (mRNA) and the protein level by reverse transcriptase/polymerase chain reaction and metabolic labeling, respectively.
RESULTS: Strong induction of IL-8 was observed in primary cultures of articular chondrocytes as well as in cartilage explants stimulated with IL-1 beta. The increased secretion of the IL-8 protein was accompanied by corresponding increases in mRNA levels. In contrast to other connective tissue cells, a peptide corresponding in molecular size to the GRO proteins was only weakly induced in cartilage explants or primary chondrocyte cultures. However, mRNA for all 3 members of the GRO family was easily detectable in cultured chondrocytes following stimulation with IL-1 beta. In explanted cartilage, mRNA for only GRO gamma was found to be induced. Newly synthesized IL-8 was slowly released from cartilage explants over a prolonged time in culture.
CONCLUSION: The results suggest that synthesis and secretion of the diverse members of the IL-8/GRO family is regulated in a tissue-specific or cell-specific manner. The slow release of IL-8 from articular cartilage following induction by IL-1 beta could establish a chemotactic gradient toward the articular surface and mediate the migration and attachment of neutrophils and lymphocytes to this tissue.