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Microglia induce CD4 T lymphocyte final effector function and death
A L Ford1, E Foulcher, F A Lemckert
1Centenary Institute of Cancer Medicine and Cell Biology, Sydney, NSW, Australia.
Abstract:
Microglia, a type of tissue macrophage, are the only cells in the central nervous system (CNS) parenchyma to express some major histocompatibility complex (MHC) class II constitutively or to upregulate expression readily. They are thought to play a role in CD4 T cell activation in autoimmune diseases such as multiple sclerosis, as well as in neurodegenerative conditions, Alzheimer's disease in particular. We show here that highly purified MHC class II+ microglia when tested directly ex vivo do indeed support an effector response by an encephalitogenic myelin basic protein-reactive CD4 T cell line from which production of the proinflammatory cytokines, interferon gamma and tumor necrosis factor, is elicited, but not interleukin (IL)-2 secretion or proliferation. After this interaction, the T cells die by apoptosis. Other nonmicroglial but CNS-associated macrophages isolated in parallel stimulate full T cell activation, including IL-2 production, proliferation, and support T cell survival. Neither CNS-derived population expresses B7.1/B7.2. Resident macrophages that terminate effector T cells in tissues constitute a novel and broadly applicable regulatory measure of particular relevance to processes of self-tolerance against sequestered antigens.
Insights
Microglia, central nervous system immune cells, elicit specific CD4 T cell responses but do not support their proliferation or survival. This suggests a regulatory role for microglia in maintaining self-tolerance, particularly in neurodegenerative diseases.
Area of Science:
- Neuroimmunology
- Central Nervous System (CNS) Biology
Background:
- Microglia are CNS-resident macrophages crucial for immune surveillance.
- They express MHC class II and are implicated in autoimmune and neurodegenerative diseases.
- Their precise role in T cell activation within the CNS remains incompletely understood.
Purpose of the Study:
- To investigate the capacity of purified microglia to activate and sustain CD4 T cell responses ex vivo.
- To compare microglia function with other CNS-associated macrophages.
- To elucidate the role of microglia in T cell regulation and self-tolerance.
Main Methods:
- Isolation and purification of MHC class II+ microglia and other CNS-associated macrophages.
- Co-culture of purified cells with an encephalitogenic myelin basic protein-reactive CD4 T cell line.
- Assessment of T cell activation markers (cytokine production, proliferation, apoptosis, survival).
Main Results:
- Microglia elicited effector responses (IFN-γ, TNF) from CD4 T cells but not IL-2 secretion or proliferation.
- T cells interacting with microglia underwent apoptosis.
- Non-microglial CNS macrophages supported full T cell activation, proliferation, and survival.
- Neither CNS-derived population expressed B7.1/B7.2 co-stimulatory molecules.
Conclusions:
- Microglia exhibit a regulatory function by eliciting effector T cell responses and promoting their apoptosis, distinct from other CNS macrophages.
- This microglial function may be critical for maintaining self-tolerance against CNS-specific antigens.
- Resident macrophages can terminate effector T cells, representing a novel regulatory mechanism in the CNS.