Microglia Induce Neurotoxic IL-17+ γδ T Cells Dependent on TLR2, TLR4, and TLR9 Activation.
BACKGROUND
Interleukin-17 (IL-17) acts as a key regulator in central nervous system (CNS) inflammation. γδ T cells are an important innate source of IL-17. Both IL-17+ γδ T cells and microglia, the major resident immune cells of the brain, are involved in various CNS disorders such as multiple sclerosis and stroke. Also, activation of Toll-like receptor (TLR) signaling pathways contributes to CNS damage. However, the mechanisms underlying the regulation and interaction of these cellular and molecular components remain unclear.


OBJECTIVE
In this study, we investigated the crosstalk between γδ T cells and microglia activated by TLRs in the context of neuronal damage. To this end, co-cultures of IL-17+ γδ T cells, neurons, and microglia were analyzed by immunocytochemistry, flow cytometry, ELISA and multiplex immunoassays.


RESULTS
We report here that IL-17+ γδ T cells but not naïve γδ T cells induce a dose- and time-dependent decrease of neuronal viability in vitro. While direct stimulation of γδ T cells with various TLR ligands did not result in up-regulation of CD69, CD25, or in IL-17 secretion, supernatants of microglia stimulated by ligands specific for TLR2, TLR4, TLR7, or TLR9 induced activation of γδ T cells through IL-1β and IL-23, as indicated by up-regulation of CD69 and CD25 and by secretion of vast amounts of IL-17. This effect was dependent on the TLR adaptor myeloid differentiation primary response gene 88 (MyD88) expressed by both γδ T cells and microglia, but did not require the expression of TLRs by γδ T cells. Similarly to cytokine-primed IL-17+ γδ T cells, IL-17+ γδ T cells induced by supernatants derived from TLR-activated microglia also caused neurotoxicity in vitro. While these neurotoxic effects required stimulation of TLR2, TLR4, or TLR9 in microglia, neuronal injury mediated by bone marrow-derived macrophages did not require TLR signaling. Neurotoxicity mediated by IL-17+ γδ T cells required a direct cell-cell contact between T cells and neurons.


CONCLUSIONS
Taken together, these results point to a crucial role for microglia activated through TLRs in polarization of γδ T cells towards neurotoxic IL-17+ γδ T cells.
Department of Neurology, Charité - Universitaetsmedizin Berlin, Berlin, Germany.
Katja
K
Derkow
Department of Neurology, Charité - Universitaetsmedizin Berlin, Berlin, Germany.
Christina
C
Krüger
Department of Neurology, Charité - Universitaetsmedizin Berlin, Berlin, Germany.
Paul
P
Dembny
Department of Neurology, Charité - Universitaetsmedizin Berlin, Berlin, Germany; Cluster of Excellence NeuroCure, Charité - Universitaetsmedizin Berlin, Berlin, Germany; Institute of Cell Biology and Neurobiology, Center for Anatomy, Charité - Universitaetsmedizin Berlin, Berlin, Germany.
Seija
S
Lehnardt
D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D000945:Antigens, Differentiation, T-Lymphocyte / Q000378:metabolism; D002478:Cells, Cultured; D004681:Encephalomyelitis, Autoimmune, Experimental / Q000276:immunology; D004789:Enzyme Activation / Q000276:immunology; D020381:Interleukin-17 / Q000096:biosynthesis*; D053583:Interleukin-1beta / Q000378:metabolism; D053645:Interleukin-2 Receptor alpha Subunit / Q000378:metabolism; D053760:Interleukin-23 Subunit p19 / Q000378:metabolism; D037181:Lectins, C-Type / Q000378:metabolism; D008264:Macrophages / Q000276:immunology; D008562:Membrane Glycoproteins / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000378:metabolism / Q000473:pathology*; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000276:immunology; D009474:Neurons / Q000276:immunology; D016692:Receptors, Antigen, T-Cell, gamma-delta / Q000378:metabolism*; D015398:Signal Transduction / Q000276:immunology; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D058504:Th17 Cells / Q000276:immunology; D051195:Toll-Like Receptor 2 / Q000235:genetics / Q000276:immunology*; D051197:Toll-Like Receptor 4 / Q000276:immunology*; D051199:Toll-Like Receptor 7 / Q000235:genetics; D051217:Toll-Like Receptor 9 / Q000276:immunology*; D000099192:CD69 Antigens
D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D020381:Interleukin-17; D053583:Interleukin-1beta; D053645:Interleukin-2 Receptor alpha Subunit; D053760:Interleukin-23 Subunit p19; D037181:Lectins, C-Type; D008562:Membrane Glycoproteins; D053594:Myeloid Differentiation Factor 88; D016692:Receptors, Antigen, T-Cell, gamma-delta; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051199:Toll-Like Receptor 7; D051217:Toll-Like Receptor 9; D000099192:CD69 Antigens; C587672:IL1B protein, mouse; C508841:Il23a protein, mouse; C507780:Myd88 protein, mouse; C493486:Tlr2 protein, mouse; C493487:Tlr4 protein, mouse; C477038:Tlr7 protein, mouse; C495370:Tlr9 protein, mouse