CD44 ligation on peripheral blood polymorphonuclear cells induces interleukin-6 production

Polymorphonuclear cells (PMNs) contribute to the initiation and progression of the immune response by mediating cytotoxicity, phagocytosis, and cytoki ne secretion. Because CD44 serves as a cytotoxic-triggering molecule on PMN s, it was hypothesized that it could also trigger cytokine production, In t his study, the effect of anti-CD44 antibodies on interleukin-6 (IL-6) produ ction in human PMNs was assessed, By using a reverse transcriptase-polymera se chain reaction, it was shown that PMNs stimulated with a mouse monoclona l or a rabbit polyclonal F(ab)(2) anti-CD44 transcribe IL-6 messenger RNA. A similar effect was obtained when an anti-CD44 antibody was replaced with hyaluronic acid (HA), Kinetic studies showed that anti CD44 and HA induced IL-6 gene transcription, initiated 3 hours after stimulation, peaked betwee n 12 and 24 hours, and disappeared after 48 hours. Analogous results were a chieved when secreted IL-6 protein was measured by enzyme-linked immunosorb ent assay in the PMN culture supernatants, To characterize which metabolic pathways regulated CD44-dependent IL-6 production in PMNs, an RNA polymeras e inhibitor, actinomycin D, and 2 protein kinase inhibitors, such as genist ein and staurosporine, were tested. Actinomycin D and genistein blocked IL- 6 production, whereas staurosporine did not, suggesting that CD44-dependent IL-6 production requires gene transcription and tyrosine kinase activity. Furthermore, the relationship between CD44 and cytokines that affect PMN fu nction, including interferon gamma (IFN gamma) and IL-2, was investigated. Without CD44 cross-linking, IFN gamma did not trigger IL-6 production. Howe ver, on CD44 cross-linking, IFN gamma produced a strong synergistic effect on IL-6 syntheses in human PMNs.