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IL-4 Inhibits the Expression of Mouse Formyl Peptide Receptor 2, a Receptor for Amyloid _1–42, in TNF--Activated Microglia^1,2

Pablo Iribarren^*, Keqiang Chen^*, Jinyue Hu^*, Xia Zhang, Wanghua Gong and Ji Ming Wang^3,*

^* Laboratory of Molecular Immunoregulation and Laboratory of Experimental Immunology, Center for Cancer Research, National Cancer Institute at Frederick, Frederick, MD 21702; and Basic Research Program, SAIC-Frederick, Frederick, MD 21702

Microglia are phagocytic cells in the CNS and actively participate in proinflammatory responses in neurodegenerative diseases. We have previously shown that TNF- up-regulated the expression of formyl peptide receptor 2 (mFPR2) in mouse microglial cells, resulting in increased chemotactic responses of such cells to mFPR2 agonists, including amyloid _1–42 (A₄₂), a critical pathogenic agent in Alzheimer’s disease. In the present study, we found that IL-4, a Th2-type cytokine, markedly inhibited TNF--induced expression of mFPR2 in microglial cells by attenuating activation of ERK and p38 MAPK as well as NF-B. The effect of IL-4 was not dependent on Stat6 but rather required the protein phosphatase 2A (PP2A) as demonstrated by the capacity of PP2A small interfering RNA to reverse the effect of IL-4 in TNF--activated microglia. Since both IL-4 and TNF- are produced in the CNS under pathophysiological conditions, our results suggest that IL-4 may play an important role in the maintenance of CNS homeostasis by limiting microglial activation by proinflammatory stimulants.

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