Tissue-resident microglia and recruited monocytes: relevance in neuroinflammation after peripheral lipopolysaccharide challenge

PERALTA RAMOS, JM; GAVIGLIO, EA; ARROYO, DS; BUSSI, C; IRIBARREN, P

Buenos Aires

Congreso; II French-Argentinean Immunology Meeting / SAI; 2015

SAI FAIC LASID

Abstract: Brain-resident microglia (Mi) and blood-derived monocytes, play essential roles in shaping the immune response in the central nervous system. These cells activate and migrate in response to chemokines produced during active immune responses and may contribute to the progression of neuroinflammation. In this study, we investigated the phenotypic and functional profile of tissue-resident microglia and recruited inflammatory monocytes (InfMo), to understand the contribution of each population in the establishment and development of a neuroinflammatory process induced by systemic TLR4 stimulation. We characterized the molecular and cellular players involved in neuroinflammation induced by lipopolysaccharide (LPS - 1.6 mg/kg) i.p. administration to C57BL/6 mice using flow cytometry combined with ex-vivo functional essays and confocal microscopy. Following stimulation with LPS, we found increased absolute number (p<0.001) of activated CD11b+ CD45low Mi and CD11b+ CD45high Ly6Chigh InfMo populations with differential production of cytokines IFN-γ (Th1), IL-17 (Th17) and IL-4 (Th2) (p<0.05) and membrane/intracellular expression of chemokine receptors CCR2+ and CX3CR1+ (p<0.001) compared with vehicle treated-mice. We next found InfMo purified by cell sorting suppressed CD4+ and CD8+ T cell proliferation (p<0.05) but that this response was restored when cells were primed ex-vivo with LPS (100 ng/ml) plus IFN-γ (20 ng/ml). Furthermore, aminoguanidine (90 uM), a nitric oxide inhibitor, enhanced T cell proliferation (p<0.01). Together, systemic stimulation of TLR4 would modulate chemokine receptors which are key for the recruitment of leukocytes in a neuroinflammatory response. These findings highlights the differences between tissue-resident versus peripheral recruited cells in an inflamed microenvironment