Microglial Phagocytosis Assay

Background

Microglia play multiple roles in the central nervous system (CNS). Upon stimulation, microglia present complicated inflammatory responses including altered gene expression and morphological changes (Heneka et al., 2014; Cunningham, 2013). Cytokines are a critical cluster of proteins among the list of altered expression molecules by activated microglia. Through the potent signaling-capable cytokine receptors expressed on astrocytes, neurons, and other brain cell types, microglia communicate, recruit, and coordinate inflammatory events (Smith et al., 2012). Besides cytokine secretion, phagocytosis, which involves morphological changes in microglia, also adds to their role as guardians of environmental homeostasis within the CNS milieu. Microglial phagocytosis of pathogens, extracellular protein aggregates, and apoptotic cell debris dampens inflammation and protects neurons (Fu et al., 2014). Apart from pathogenic conditions, microglial phagocytosis is also involved in CNS development and synaptogenesis through eliminating nonfunctional synapses. Deficient or excess microglial phagocytic ability could lead to abnormal synaptic connections and deposits of aggregated proteins (Schafer et al., 2012; Lian et al., 2016). Here we describe a protocol for measuring microglial phagocytic ability using in vitro cultured primary microglia. To mimic exogenous particles and protein aggregates, we used latex beads and amyloid β protein as the substrates for microglia to engulf.