IL6 and neuroblastoma: Microglia constitutively express C1q, whilst the cytokines IL-1α, IL-1β, TNFα, and IL-6 can stimulate the secretion of C1r, C1s, and C3 from microglia, astrocytes, and neuroblastoma cells, and C4 can be secreted in response to IFNγ and IL-6, but complement inhibitor C1-Inh is only secreted in response to IFNγ.