Tannins are plant-derived water-soluble polyphenols with wideranging biological activities. The mechanisms underlying the anti-inflammatory effect of tannins are not fully understood and may be the result of inhibition of poly(ADP-ribose) (PAR) glycohydrolase (PARG), the main catabolic enzyme of PAR metabolism. Therefore, we set out to investigate the mechanism of the anti-inflammatory effect of gallotannin (GT) in A549 cells with special regard to the role of poly(ADP-ribosyl)ation. Using an inflammation-focused low-density array and reverse transcription-polymerase chain reaction, we found that GT suppressed the expression of most cytokines and chemokines in cytokine-stimulated A549 cells, whereas the PARP inhibitor PJ-34 only inhibited few transcripts. Activation of the transcription factors, nuclear factor B (NF-B) and activator protein 1 (AP-1), was blocked by GT, whereas PJ-34 only suppressed NF-B activation but not AP-1 activation. GT also inhibited IB phosphorylation and nuclear translocation of NF-B, but PJ-34 had no effect on these upstream events. In the AP-1 pathway, GT treatment, even in the absence of cytokines, caused maximal phosphorylation of c-Jun N-terminal kinase and c-Jun. GT also caused a low-level phosphorylation of p38, extracellular signal-regulated kinases 1 and 2, activating transcription factor2, and cAMP-response element-binding protein but inhibited cytokine-induced phosphorylation of these kinases and transcription factors. GT inhibited protein phosphatases 1 and 2A, which may explain the increased phosphorylation of mitogenactivated protein kinase and their substrates. GT exerted potent antioxidant effect but failed to cause PAR accumulation. In summary, the potent inhibitory effects of GT on the transcription of cytokine and chemokine genes are probably not related to PARG inhibition. Inhibition of AP-1 activation and upstream signaling events may be responsible for the effects of GT.Tannins are water-soluble polyphenols that are widely distributed in the plant kingdom, including food grains and fruits. So far, more than a thousand different tannins have been characterized and ordered into four major groups: 1) gallotannins (GT), 2) ellagitannins, 3) complex, and 4) condensed tannins, with gallotannins and ellagitannins considered the most widespread types. The common structural elements of all tannins include one or more polyol units (mostly D-glucose) and one or more polyphenols (gallic acid, 3,4,5-trihydroxyl benzoic acid).The simplest hydrolyzable tannin, gallotannin, is a mixture of polygalloyl esthers of glucose. Gallotannin and other tannins have been shown to exert various biological effects ranging from anti-inflammatory to anticancer and antiviral effects (Fong et al., 1972;Mota et al., 1985;Uchiumi et al., 1996;Van Molle et al., 2000;Feldman et al., 2001). The mechanisms underlying the anti-inflammatory effect of tannins include the scavenging of radicals (antioxidant effect) (Hagerman et al., 1999) and inhibition of the expression of