No abstract

The IFN-γ-inducible chemokines CXCL9 and CXCL10 bind to CXCR3 and are implicated in the pathogenesis of T-cell-mediated immunity in the CNS. However, the cellular localization of these chemokines differs with CXCL9 produced by macrophage/microglia (M/M) while CXCL10 is produced by both M/M and astrocytes. Here we determined the mechanism for the M/M-restricted expression of the Cxcl9 gene induced by IFN-γ. Of a number of transcription factors involved with IFN-γ-mediated gene regulation, PU.1 was present constitutively in murine M/M but not in astrocytes. Both in the brain and in culture, PU.1 was localized exclusively to the nucleus of M/M cells. ChIP analysis revealed that STAT-1, PU.1 and IRF8 were bound to the CXCL9 promoter in IFN-γ-treated M/M, whereas in astrocytes STAT-1 alone bound to the CXCL9 promoter. STAT-1 but not IRF8 was critical for IFN-γ-induced expression of both the Cxcl9 and Cxcl10 genes in M/M and in M/M and astrocytes, respectively. The siRNA-mediated knockdown of PU.1 in M/M markedly impaired IFN-γ induced CXCL9 but not STAT1 or IRF8. D1A astrocyte cells showed partial reprogramming to a myeloid phenotype after transduction with PU.1 with expression of CD11b and acquisition of IFN-γ-induced CXCL9. Thus, while IFN-γ is a pivotal mediator of both Cxcl9 and Cxcl10 gene expression, this cytokine differentially induces the expression of CXCL9 in myeloid cells through a mechanism that is determined by PU.1. Support: NIH NS044905.

The chemokine receptor CXCR3 binds CXCL9, CXCL10 and CXCL11 and promotes the trafficking of activated T-cells. Although these chemokines are highly elevated in the CNS in MS and the animal model, experimental autoimmune encephalomyelitis (EAE), their role is unknown. Here we show that while IFN-γ is the principal mediator of CXCR3 ligand gene expression in the CNS in EAE, the cellular localization of the individual chemokine genes is divergent suggesting functional specialisation of the CXCR3 ligand chemokines. Transgenic mice (GF-) were generated with astrocyte-production of CXCL9, CXCL10 or CXCL11. These mice do not develop neurological disease. In GF-CXCL10 and -CXCL11 mice, modest non-reactive leukocytic infiltrates were seen in the CNS. Thus, these chemokines when produced chronically are a poor stimulus for the CNS recruitment and activation of T-cells. The role of CXCR3 signaling in MOG-induced EAE was examined in CXCR3 KO mice and in GF-CXCL9, -CXCL10 or -CXCL11 mice. CXCR3 KO, GF-CXCL9 and -CXCL11 mice had more severe EAE with widely disseminated demyelinating lesions throughout the CNS. In CXCR3 KO mice with EAE the number of suppressor Treg cells in the brain was reduced. Thus, in EAE, CXCR3 chemokine ligands:have non-redundant functions,are not involved in the initial recruitment of effector T-cells to the CNS, andretain T-cells to the perivascular space and foster Treg cell interactions thereby limiting lesion spread and tissue destruction. Support: NIH NS044905.