Polyunsaturated Fatty Acids Block Dendritic Cell Activation and Function Independently of NF-κB Activation

Maximilian Zeyda,Marcus D Säemann,Karl M Stuhlmeier,Daniel G Mascher,Peter N Nowotny,Gerhard J Zlabinger,Werner Waldhäusl,Thomas M Stulnig

doi:10.1074/jbc.m410000200

Abstract

Polyunsaturated fatty acids (PUFAs) modulate immune responses leading to clinically significant beneficial effects in a variety of inflammatory disorders. PUFA effects on T cells have been extensively studied, but their influence on human dendritic cells (DCs), which are the most potent antigen-presenting cells and play a key role in initiating immune responses, has not been elucidated so far. Here we show that PUFAs of the n-3 and n-6 series (arachidonic and eicosapentaenoic acid) affect human monocyte-derived DC differentiation and inhibit their activation by LPS, resulting in altered DC surface molecule expression and diminished cytokine secretion. Furthermore, the potency to stimulate T cells was markedly inhibited in PUFA-treated DCs. The PUFA-mediated block in LPS-induced DC activation is reflected by diminished TNF-alpha, IL-12p40, CD40, and COX-2 mRNA levels. Strikingly, typical LPS-induced signaling events such as degradation of IkappaB and activation of NF-kappaB were not affected by PUFAs, even though DC membrane lipid composition was markedly altered. Arachidonic and eicosapentaenoic acid both altered DC prostaglandin production, but inhibitors of cyclooxygenases and lipoxygenases did not abolish PUFA effects, indicating that the observed PUFA actions on DCs were independent of autoregulation via eicosanoids. These data demonstrate a unique interference with DC activation and function that could significantly contribute to the well known anti-inflammatory effects of PUFAs.

Highlights

Polyunsaturated fatty acids (PUFAs) modulate immune responses leading to clinically significant beneficial effects in a variety of inflammatory disorders
To elucidate PUFA effects on these events, isolated human monocytes were differentiated to dendritic cells (DCs) in the presence of 20 ␮M of a variety of fatty acids
In PUFA-treated DCs expression of HLA-DR was not altered, while CD40, CD80, and mannose receptor (MR) expression was reduced by about 50%, irrespective of whether the n-6 PUFA AA or the n-3 PUFA EA was used (Fig. 1)

Summary

EXPERIMENTAL PROCEDURES

Cells and Fatty Acid Treatment—Peripheral blood mononuclear cells were isolated from buffy coats obtained from healthy donors by density gradient centrifugation over Ficoll-Paque (Amersham Biosciences) and depleted from T cells by sheep erythrocyte rosetting. The medium was mixed for 1 h to allow binding of fatty acids to albumin prior to addition to cells at indicated concentrations. Nuclear extracts (2 ␮g of protein) were incubated with 120,000 cpm labeled probe in the presence of 3 ␮g of poly(dI-dC) at room temperature for 20 min. This mixture was separated on a 6% polyacrylamide gel in Tris/glycine/EDTA buffer at pH 8.5. Quantitation of Specific mRNA—Total RNA of fatty acid-treated DCs, stimulated for 4 to 8 h with 100 ng/ml LPS, was isolated using TRIzol reagent (Invitrogen) according to the manufacturer’s instruction. Comparisons were performed by two-tail unpaired Student’s t test and a p Ͻ 0.05 was considered statistically significant

RESULTS

Fatty acid

DISCUSSION