To verify which cytokines microglia use to signal A1 induction, we purified microglia by immunopanning and determined which cytokines are secreted by resting and LPS-activated microglia. Levels of Il-1α, TNFα and C1q were all significantly elevated after microglial activation (Fig. 1b, c). Il-1β secretion also increased in LPS-activated MCM, but was unable to induce expression of A1 transcripts (Fig. 1a). We also tested a range of other microglia-secreted cytokines that were unable to induce A1s (Extended Data Fig. 2). The combination of Il-1α, TNFα and C1q however, closely mimicked that of LPS-reactive MCM (Fig. 1a).
