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Fig. 2 | Journal of Neuroinflammation

Fig. 2

From: The semantics of microglia activation: neuroinflammation, homeostasis, and stress

Fig. 2

Contrast between neuroinflammation and parainflammation. Neuroinflammation (left) describes immune-driven pathology which occurs in the course of disease, injury, or infection in the brain. This tissue state can be identified by four common molecular and cellular hallmarks illustrated on the left. These are: (1) high levels of pro-inflammatory cytokines, (2a) microglia and (2b) peripheral macrophage activation, (3) infiltration of peripheral leukocytes (e.g., bone-derived monocytes, T cells) to the parenchyma, and tissue damage such as (4a) BBB breakdown and (4b) neuron death. Neuro-immune systems can also be engaged by homeostatic challenges (i.e., psychological stress), leading to an intermediate tissue state termed parainflammation (right). While a formal definition of parainflammation is yet to be widely accepted in neuroscience, neuro-immune interactions previously reported in parainflammatory contexts are shown on the right. These include: (1) microglial recruitment of bone-derived monocytes to the perivascular space, (2) changes in cytokine signaling between neurons and microglia, (3) microglia-mediated neuronal remodeling, and (4) diffusion of small signaling peptides across the BBB

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