Expression of cytokines by human astrocytomas following stimulation by C3aand C5a anaphylatoxins: Specific increase in interleukin-6 mRNA expression

C3a and C5a anaphylatoxins are two proinflammatory peptides generated durin g complement activation that act through distinct G(i) protein-coupled rece ptors named C3aR and C5aR, respectively. We have demonstrated previously th at human astrocytes expressed C3aR and C5aR constitutively and were able to produce a functional complement. In this study, we examined the effect of an anaphylatoxin stimulation on cytokine expression by human astrocyte cell lines. Interleukin (II)-1 beta, IL-6, tumor necrosis factor-alpha, and tra nsforming growth factor-beta mRNA expression was studied by quantitative RT -PCR. Whereas Il-1 beta, tumor necrosis factor-alpha, and transforming grow th factor-beta mRNA levels remained unchanged, stimulation of astrocytoma c ells (T98G, CB193, U118MG) by C3a, C5a, and peptidic C3aR and G5aR agonists induced an increase in the IL-6 mRNA level. The amount of IL-6 was markedl y increased at 3 and 6 h and returned to the basal level at 9 h of stimulat ion. This response was specific, because pretreatment of cells with pertuss is toxin or with polyclonal anti-C3aR or anti-C5aR antibodies completely bl ocked the IL-6 mRNA increase. The IL-6 response was also investigated at th e protein level, but IL-6 protein was detected neither in cell lysates nor in supernatants of stimulated cells. The anaphylatoxin-mediated transcripti onal activation of IL-6 gene suggests that C3a and C5a could play a role in priming glial cells during the inflammatory process in the brain.