Figure 6.

Temporal profile of unconjugated bilirubin-induced (UCB) activation of inflammatory pathways: a comparison between microglia and astrocytes. Increased and equivalent release of tumor necrosis factor (TNF)-α (A) is determined by UCB on both astrocytes and microglia. However, secretion of interleukin (IL)-1β (B) by astrocytes is much higher in microglia and earlier produced upon UCB challenge than in astrocytes. Initial effects of UCB at the level of IL-6 release (C) are of opposite signals. While IL-6 production by astrocytes is depressed in the first 4 h of incubation with UCB before being enhanced, IL-6 secretion by microglia is almost immediately induced by UCB. These timely differences in the secretion of pro-inflammatory cytokines between astrocytes and microglia should reside in the former activation of nuclear factor (NF)-κB and mitogen-activated protein kinases (MAPKs) (D) in microglia than is astrocytes. These features corroborate the belief that microglia is activated earlier than astrocytes, thus promoting astrocytic activation. Data, presented as mean ± SEM, derived from Fernandes et al. (2006) and Silva et al. (2010).