To ensure no other factors secreted by LPS-activated microglia could also make A1s, we collected LPS-activated MCM and pre-treated it with neutralizing antibodies to Il-1α, TNFα, and C1q. This pre-treated MCM was unable to induce reactive astrocyte genes (Fig. 1a, Extended Data Fig. 3e). Thus Il-1α, TNFα and C1q together are sufficient to induce the A1 phenotype, and are necessary for LPS-reactive microglia to induce A1s in vitro.
