Chemokines are differentially expressed by astrocytes, microglia and inflammatory leukocytes in Toxoplasma encephalitis and critically regulated by interferon-gamma.

The intracerebral formation of inflammatory infiltrates is a complex process, which may be regulated by chemokines. This study defines the kinetics and cellular sources of T cell- and macrophage-attracting chemokines in murine Toxoplasma encephalitis (TE) by ribonuclease protection assay, reverse transcription-PCR, in situ hybridization, and immunohistochemistry. Whereas astrocytes were the major source of interferon (IFN)-gamma-inducible protein-10 (CRG-2/IP-10) and monocyte chemoattractant protein (MCP)-1, microglia expressed RANTES, monokine induced by IFN-gamma (MuMIG) and occasionally CRG-2/IP-10 RNA. Despite being ubiquitously activated, only astrocytes and microglia confined to inflammatory infiltrates expressed chemokine genes. Intracerebral leukocytes transcribed RANTES, MuMIG, and occasionally CRG-2/IP-10 and MCP-1. IFN-gamma-deficient mice failed to produce CRG-2/IP-10, MuMIG, RANTES and expressed macrophage inflammatory protein (MIP-1)alpha, MIP-1 beta, and MCP-1 mRNA at reduced levels, functionally resulting in a strongly reduced recruitment of leukocytes across the blood-brain barrier and prevented their further invasion of the brain parenchyma. Since T cells are the single source of IFN-gamma in TE, these findings indicate that T cells pave the way of leukocytes to parenchymatous parasites via IFN-gamma.