Astrocyte gp130 Expression Is Critical for the Control of Toxoplasma Encephalitis

Toxoplasma gondii infects astrocytes, neurons and microglia cells in the CNS and, after acute encephalitis, persists within neurons. Robust astrocyte activation is a hallmark of Toxoplasma encephalitis (TE); however, the in vivo function of astrocytes is largely unknown. To study their role in TE we generated C57BL/6 GFAP-Cre gp130 fl/fl mice (where GFAP is glial fibrillary acid protein), which lack gp130, the signal-transducing receptor for IL-6 family cytokines, in their astrocytes. In the TE of wild-type mice, the gp130 ligands IL-6, IL-11, IL-27, LIF, oncostatin M, ciliary neurotrophic factor, B cell stimulating factor, and cardiotrophin-1 were up-regulated. In addition, GFAP + astrocytes of gp130 fl/fl control mice were activated, increased in number, and efficiently restricted inflammatory lesions and parasites, thereby contributing to survival from TE. In contrast, T. gondii - infected GFAP-Cre gp130 fl/fl mice lost GFAP + astrocytes in inflammatory lesions resulting in an inefficient containment of inflammatory lesions, impaired parasite control, and, ultimately, a lethal necrotizing TE. Production of IFN-γ and the IFN-γ-induced GTPase (IGTP), which mediate parasite control in astrocytes, was even increased in GFAP-Cre gp130 fl/fl mice, indicating that instead of the direct antiparasitic effect the immunoregulatory function of GFAP-Cre gp130 fl/fl astrocytes was disturbed. Correspondingly, in vitro infected GFAP-Cre gp130 fl/fl astrocytes inhibited the growth of T. gondii efficiently after stimulation with IFN-γ, whereas neighboring noninfected and TNF-stimulated GFAP-Cre gp130 fl/fl astrocytes became apoptotic. Collectively, these are the first experiments demonstrating a crucial function of astrocytes in CNS infection.