Interleukin-4, Interleukin-10, and Interleukin-1-Receptor Antagonist But Not Transforming Growth Factor- Induce Ramification and Reduce Adhesion Molecule Expression of Rat Microglial Cells Florentina Wirjatijasa, 1,2 Faramarz Dehghani, 2 Roman A. Blaheta, 3 Horst-Werner Korf, 2 and Nils P. Hailer 1 * 1 University Hospital for Orthopaedic Surgery Friedrichsheim, Frankfurt, Germany 2 Institute of Anatomy II, Johann Wolfgang Goethe-University, Frankfurt, Germany 3 Department of General Surgery, Hospital of the Johann Wolfgang Goethe-University, Frankfurt, Germany The activity of microglial cells is strictly controlled in order to maintain central nervous system (CNS) immune privilege. We hypothesized that several immunomodula- tory factors present in the CNS parenchyma, i.e., the Th2-derived cytokines interleukin (IL)-4 and IL-10, interleukin-1-receptor-antagonist (IL-1-ra), or transform- ing growth factor (TGF)- can modulate microglial mor- phology and functions. Microglial cells were incubated with IL-4, IL-10, IL-1-ra, TGF-, or with astrocyte condi- tioned media (ACM) and were analyzed for morphologi- cal changes, expression of intercellular adhesion mole- cule (ICAM)-1, and secretion of IL-1 or tumor necrosis factor (TNF)-. Whereas untreated controls showed an amoeboid morphology both Th2-derived cytokines, IL-1- ra, and ACM induced a morphological transformation to the ramified phenotype. In contrast, TGF--treated mi- croglial cells showed an amoeboid morphology. Even combined with the neutralizing antibodies against IL-4, IL-10, or TGF- ACM induced microglial ramification. Furthermore, ACM did not contain relevant amounts of IL-4 and IL-10, as measured by enzyme-linked immu- nosorbent assay (ELISA). Flow cytometry showed that lipopolysaccharide (LPS)-induced ICAM-1-expression on microglial cells was strongly suppressed by ACM, significantly modulated by IL-4, IL-10, or IL-1-ra, but not influenced by TGF-. The LPS-induced secretion of IL-1 and TNF- was only reduced after application of ACM, whereas IL-4 or IL-10 did not inhibit IL-1- or TNF- secretion. TGF- enhanced IL-1- but not TNF- secretion. In summary, we demonstrate that IL-4, IL-10, and IL-1-ra induce microglial ramification and reduce ICAM-1-expression, whereas the secretion of proinflam- matory cytokines is not prevented. TGF- has no mod- ulating effects. Importantly, unidentified astrocytic fac- tors that are not identical with IL-4, IL-10, or TGF- possess strong immunomodulatory properties. © 2002 Wiley-Liss, Inc. Key words: quantitative morphometry; ICAM-1; FACS- analysis; ELISA; CNS immune privilege Microglial cells are resident macrophages of the cen- tral nervous system (CNS) derived from blood monocytes that populate the brain during ontogenesis (Rio-Hortega 1932; Ling and Wong, 1993). In the adult CNS, ramified microglia show little or no expression of major histocom- patibility complex (MHC) or adhesion molecules and no secretion of proinflammatory cytokines or free radicals (Ling and Wong, 1993; Kreutzberg, 1996). In cooperation with the blood brain barrier and the prevalence of immu- nomodulatory cytokines such as interleukin (IL)-4, and IL-10, resting microglial cells contribute to the immune privilege of the CNS (Owens et al., 1994). Several studies have shown that astrocytes play a key role in maintaining the resting, deactivated state of microglial cells by releasing immunomodulatory factors (Sievers et al., 1994; Wilms et al., 1997; Vincent et al., 1997; Hailer et al., 1998). In response to pathological events, microglial cells are rapidly activated, reflected by proliferation, migration Contract grant sponsor: Deutsche Forschungsgemeinschaft; Contract grant number: Ha 2721/1-3; Contract grant sponsor: Paul und Ursula Klein- Stiftung; Contract grant sponsor: Stiftung Friedrichsheim; Contract grant sponsor: Medical Faculty of the Johann Wolfgang Goethe-University. Florentina Wirjatijasa and Faramarz Dehghani contributed equally to this paper. *Correspondence to: Dr. Nils P. Hailer, University Hospital for Ortho- paedic Surgery, Friedrichsheim, Marienburgstr. 2, D-60528 Frankfurt, Fed- eral Republic of Germany. E-mail: hailer@em.uni-frankfurt.de Received 12 October 2001; Revised 28 February 2002; Accepted 5 March 2002 Published online 25 April 2002 in Wiley InterScience (www. interscience.wiley.com). DOI: 10.1002/jnr.10254 Journal of Neuroscience Research 68:579 –587 (2002) © 2002 Wiley-Liss, Inc.