Effects of IL-10 and IL-4 on LPS-induced transcription factors (AP-1, NF-IL6 and NF-kappa B) which are involved in IL-6 regulation. 
Interleukin-10 (IL-10), like IL-4, is known to inhibit cytokine expression in activated human monocytes. We showed that both IL-10 and IL-4 inhibit LPS-induced IL-6 mRNA and protein expression by inhibiting the transcription rate of the IL-6 gene. The strong inhibition of the IL-6 transcription rate prompted us to study the effect of IL-10 and IL-4 on the expression of transcription factors. We questioned whether or not IL-10 and IL-4 affected the expression of transcription factors that are known to be involved in the control of the IL-6 transcription rate, namely activator protein-1 (AP-1), nuclear factor IL-6 (NF-IL6), and nuclear factor kappa B (NF-kappaB). In electrophoretic mobility shift assays (EMSAs) we showed that IL-10 and IL-4 inhibited LPS-induced AP-1 binding activity. The inhibiting effect of IL-4 was slightly more pronounced than that of IL-10. Downregulation of LPS-induced AP-1 was accompanied, and thus possibly explained, by a reduced expression at mRNA level of the two major components of the AP-1 complex, namely c-fos and c-jun as determined by Northern experiments. Binding activity of NF-IL6 was also strongly inhibited by IL-4 whereas IL-10 showed no effect. NF-IL6 mRNA levels were not affected by IL-10 or IL-4, suggesting that IL-4 affects binding activity of preexisting NF-IL6. Neither IL-10 nor IL-4 inhibited LPS-induced NF-kappa B binding activity. In agreement with this finding, Northern experiments where p65 and p105 mRNA levels were determined, demonstrated that expression of these components of the NF-kappa B transcription factor were not affected by IL-10 or IL-4. Furthermore, neither IL-10 nor IL-4 showed any effect on I-kappa B mRNA expression as determined by Northern experiments. Thus, IL-10 and IL-4 similarly affect IL-6 expression. However, for IL-4 this was accompanied with a reduction of AP-1 and NF-IL6 binding activity whereas IL-10 only inhibited AP-1 binding activity.