Objectives: Brain-resident microglia (Mi) and blood-derivedmonocytes, play essential roles in shaping the immune response in the centralnervous system. These cells activate and migrate in response to chemokines producedduring active immune responses and may contribute to the progression ofneuroinflammation. In this study, we investigated the phenotypic and functionalprofile of tissue-resident microglia and recruited inflammatory monocytes(InfMo), to understand the contribution of each population in the establishmentand development of a neuroinflammatory process induced by systemic TLR4stimulation.
Methods & Results: We characterized the molecular andcellular players involved in neuroinflammation induced by lipopolysaccharide(LPS - 1.6 mg/kg) i.p. administration to C57BL/6 mice using flow cytometrycombined with ex-vivofunctional essays and confocal microscopy. Following stimulation with LPS, wefound increased absolute number (p<0.001) of activated CD11b+ CD45lowMi and CD11b+ CD45high Ly6Chigh InfMopopulations withdifferential production of cytokines IFN-γ(Th1), IL-17 (Th17) and IL-4 (Th2) (p<0.05) andmembrane/intracellular expression of chemokine receptors CCR2+ and CX3CR1+(p<0.001) comparedwith vehicle treated-mice. We next found InfMo purified by cell sorting suppressedCD4+ and CD8+ T cell proliferation(p<0.05) but that this response was restoredwhen cells were primed ex-vivo withLPS (100 ng/ml) plus IFN-γ (20 ng/ml). Furthermore, aminoguanidine (90 uM), anitric oxide inhibitor, enhanced T cell proliferation (p<0.01).
Conclusions: Together, systemic stimulation of TLR4 wouldmodulate chemokine receptors which are key for the recruitment of leukocytes ina neuroinflammatory response. These findings highlights the differences betweentissue-resident versus peripheral recruited cells in an inflamed microenvironment.
