Interleukin-4-inhibited mRNA expression in mixed rat glial and in isolated microglial cultures

Interleukin-4 (IL-4) likely is one of the key players in the concert of immunosuppressive factors in brain. Therefore, influences of the cytokine on mRNA expression of endogenous mediators of inflammation, such as cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), tumor necrosis factor-alpha (TNF-alpha), interferon-inducible protein 10 (IP-10), interleukin-3 receptor-beta (IL-3R-beta), and of another antiinflammatory cytokine, IL-10, have been evaluated in the present study by semi-quantitative RT-PCR. Primary rat mixed glial cultures and isolated microglial cells, the resident immunocytes of the brain, have been used as rich sources of these mRNAs in response to the bacterial cell wall component lipopolysaccharide (LPS). Time-course studies showed peak levels of LPS-increased mRNAs at approximately 4 h. Interestingly, IL-10 mRNA was elevated also upon the LPS-stimulus. IL-4, given 30 min before LPS, inhibited increases of all mRNAs significantly, including IL-10 mRNA. IL-4, however, induced peroxisome proliferator-activated receptor (PPAR)-gamma in cultured microglia. This induction was completely inhibited by simultaneous administration of LPS. The data confirms IL-4 as an important antiinflammatory cytokine and gives some idea of cross-talk between intracellular signaling evoked by pro- and antiinflammatory substances.