Aldh1l1-Cre/ERT2 Drives Flox-Mediated Recombination in Peripheral and CNS Infiltrating Immune Cells in Addition to Astrocytes During CNS Autoimmune Disease.

INTRODUCTION: The transgenic murine Cre/loxP system is deployed to investigate the role of central nervous system (CNS) cell-specific gene alterations in both healthy conditions and models of neurologic disease. The Aldh1l1-Cre/ERT2 line is widely used to target astrocytes with high coverage and specificity within the CNS. Specificity outside the CNS, however, has not been well-characterized, and Aldh1l1-Cre/ERT2-mediated recombination within the spleen has been reported. In many CNS diseases, infiltrating immune cells from the periphery drive or regulate pathogenesis. We tested whether flox-mediated recombination from Aldh1l1-Cre/ERT2 occurs in immune cells in addition to astrocytes and whether these cells traffic from the spleen into the spinal cord during experimental autoimmune encephalomyelitis (EAE), a model of CNS autoimmune disease.

METHODS: Two astrocyte-targeted mouse lines were generated with the red fluorescent reporter, tdTomato, by crossing the Cre-recombinase lines, Tg(Aldh1l1-Cre/ERT2)1Khakh and Tg(Gfap-Cre)73.12Mvs, with the reporter line, Gt(ROSA)26Sor. Aldh1l1-Cre/ERT2 was activated with 5 days of intraperitoneal tamoxifen, whereas Gfap-Cre was constitutively active. EAE was induced 2 weeks after tamoxifen, and then spleens and spinal cords were harvested and processed for flow cytometry at various time points after disease onset in EAE versus healthy controls.

RESULTS: In EAE, Aldh1l1-Cre/ERT2, but not Gfap-Cre, induced multiple tdTomato+ immune cell subpopulations in the spleen and spinal cord, including macrophages, monocytes, neutrophils, eosinophils, B cells, CD4+, and CD8+ T cells.

CONCLUSION: Use of Aldh1l1-Cre/ERT2 should therefore account for recombination in both astrocytes and immune cells in disease models involving peripheral immune cell infiltration into the CNS.