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Innate immunity in the central nervous system
Richard M. Ransohoff, Melissa A. Brown
Richard M. Ransohoff, Melissa A. Brown
Published April 2, 2012
Citation Information: J Clin Invest. 2012;122(4):1164-1171. https://doi.org/10.1172/JCI58644.
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Innate immunity in the central nervous system

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Abstract

Immune responses in the CNS are common, despite its perception as a site of immune privilege. These responses can be mediated by resident microglia and astrocytes, which are innate immune cells without direct counterparts in the periphery. Furthermore, CNS immune reactions often take place in virtual isolation from the innate/adaptive immune interplay that characterizes peripheral immunity. However, microglia and astrocytes also engage in significant cross-talk with CNS-infiltrating T cells and other components of the innate immune system. Here we review the cellular and molecular basis of innate immunity in the CNS and discuss what is known about how outcomes of these interactions can lead to resolution of infection, neurodegeneration, or neural repair depending on the context.

Authors

Richard M. Ransohoff, Melissa A. Brown

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Figure 1

Innate immunity in the periphery and CNS.

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Innate immunity in the periphery and CNS.
(A) In the face of a periphera...
(A) In the face of a peripheral infection, innate immune cells prime and instruct T lymphocytes. Tissue DCs internalize microbial protein antigens, process them into peptides, and display them on their surfaces with MHC class II molecules; migrate to draining lymph nodes; and present antigens to naive CD4+ T cells. DCs direct the quality of the subsequent inflammatory response by decoding distinctive pathogen-associated signals and transmitting this information to T cells in the form of regulatory cytokines such as IL-12 (for Th1), IL-4 (Th2), or IL-6/TGF-β (Th17). In addition, lymph node environmental cues can provide information about the site of infection (gut, skin, or other). Armed with this information, effector T cells migrate to infected tissues. Upon reactivation, Th1, Th2, and Th17 cells express phenotype-defining cytokines that act on resident and recruited innate cells, which operate collectively with factors such as complement to clear the infection. (B) Resident microglia and astrocytes exert multiple functions in the CNS, including protective and restorative responses to CNS infection or injury. Cytokines and chemokines expressed by resident CNS cells also promote the recruitment of circulating lymphocytes and myeloid cells from the periphery to assist in pathogen clearance. Innate responses in the CNS cannot directly initiate adaptive immunity. Innate CNS reactions also occur during neuroinflammatory disorders and utilize many of the same components as do host defense responses.

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ISSN: 0021-9738 (print), 1558-8238 (online)

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