Microglia cells are specialized macrophages, found throughout the brain and spinal cord. Two functional distinct populations have been characterized on the basis of the expression of an antibody (5D4) reactive keratan sulfate proteoglycan on their cell surface. Cells with lower expression (5D4low) are more immunologically active than their highly expressing (5D4high) counterparts. 5D4high/5D4low- comparative microarray data revealed many differentially expressed genes which were of particular

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... terest with respect to microglia development and function. Five genes, which showed an increased expression rate in 5D4high microglia cells, were analyzed: Cadm1, Dlx2, Dscam, Tef and Twist-2. All of them, besides Cadm1, were found to be active on the mRNA level in rat microglia cells. The role of Dscam in the immune system of Drosophila and its ability to make homo- and heterophilic interactions was very interesting in this aspect. Hence, it was the most promising aspirant for further investigations. We focused on Dscam and examined its expression on mRNA and protein level in rat microglia cells. Additionally, a functional knock-down experiment was performed. Even though Dscam expression was shown several times, we could not clearly confirm its expression in rat microglia cells, since the presence of false positive cells, possible due to Dscam positive contaminants could not be completely excluded. Future studies should be done to further address the possible role of Dscam in mammalian immune responses. Helpful in this regard would be more and novel literature about microglia diversity as well as the development of an appropriate antibody.