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-gamma and the IFN-gamma-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-gamma, 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.

Protein kinase C-theta critically regulates the proliferation and survival of pathogen-specific T cells in murine listeriosis.

Protein kinase C-theta (PKC-theta) is essential for the activation of T cells in autoimmune disorders, but not in viral infections. To study the role of PKC-theta in bacterial infections, PKC-theta(-/-) and wild-type mice were infected with Listeria monocytogenes (LM). In primary and secondary listeriosis, the numbers of LM-specific CD8 and CD4 T cells were drastically reduced in PKC-theta(-/-) mice, resulting in increased CFUs in spleen and liver of both PKC-theta(-/-) C57BL/6 and BALB/c mice. Furthermore, immunization with peptide-loaded wild-type dendritic cells induced LM-specific CD4 and CD8 T cells in wild-type but not in PKC-theta(-/-) mice. In listeriosis, transfer of wild-type T cells into PKC-theta(-/-) mice resulted in a normal control of Listeria, and, additionally, a selective expression of PKC-theta in LM-specific T cells was sufficient to drive a normal proliferation and survival of these T cells in LM-infected PKC-theta(-/-) recipients, illustrating a cell-autonomous function of PKC-theta in LM-specific T cells. Conversely, adoptively transferred PKC-theta(-/-) T cells were partially rescued from cell death and proliferated in LM-infected wild-type recipients, demonstrating that a PKC-theta deficiency of LM-specific T cells can be partially compensated for by a wild-type environment. Additionally, in vitro experiments showed that only the addition of IL-2, but not an inhibition of caspase-3, induced proliferation and prevented death of PKC-theta(-/-) T cells stimulated with LM-infected wild-type dendritic cells, further demonstrating that the impaired proliferation and survival of PKC-theta(-/-) T cells in listeriosis is not intrinsically fixed and can be experimentally improved.