Interleukin-8 (IL-8: CXCL8) and growth related oncogene α (GROα: CXCL1) are members of the CXC chemokines. In the present study, we explored the functional distinction between these CXC chemokines in the regulation of neutrophil infiltration. Injection of either rabbit IL-8 or GROα (10 μg each) into rabbit knee joints resulted in a massive neutrophil infiltration in the joints. At their peak time point (6 hours), the number of neutrophils induced by IL-8 was more than that induced by GROα. Each chemokine induced the other chemokine in the joints. TNFα activity was induced in the joints after administration of GROα, but not IL-8. Treatment with anti-GROα mAb and/or anti-TNFα mAb failed to inhibit IL-8-induced neutrophil infiltration. In contrast, either anti-IL-8 IgG or anti-TNFα mAb decreased GROα-induced response, and the inhibition was further enhanced by coadministration of these antibodies. Thus, it appears that IL-8 acts directly, whereas GROα acts indirectly, in part, on neutrophil infiltration. The distinct difference in TNFα production between IL-8 and GROα was further investigated. In vitro, GROα induced TNFα activity in cultured synovial cells, the cells producing TNFα in the joints after GROα-injection. However, IL-8 failed to produce TNFα activity from the cells, although equivalent levels of the mRNA expression were induced by IL-8 as compared with GROα. When recombinant rabbit TNFα was incubated with synovial fluids obtained at 2 hours after IL-8 injection, the resultant TNFα activity was significantly decreased, an event that was completely restored by a serine protease inhibitor, phenylmethylsulphonyl fluoride (PMSF). Furthermore, TNFα activity was unveiled in the joints when IL-8 was intra-articularly injected with PMSF. These data suggest that TNFα is degraded by serine protease(s) in the case of IL-8. Taken together, the data clearly demonstrate the functional distinction between IL-8 and GROα, which may influence the inflammatory responses.
ASJC Scopus subject areas
- Pathology and Forensic Medicine
- Molecular Biology
- Cell Biology