Astrocyte activation correlates with cytokine production in central nervous system of Trypanosoma brucei brucei-infected mice.

BACKGROUND

During the late-stage disease associated with human African trypanosomiasis, caused by infection with either Trypanosoma gambiense or T. rhodesiense, parasites invade the central nervous system (CNS), eventually leading to development of CNS pathology. This can be exacerbated by subcurative chemotherapy. The mechanisms through which the inflammatory processes within the CNS are controlled remain unclear.

EXPERIMENTAL

DESIGN

Mice infected with T. b. brucei were treated with a trypanocidal drug regimen on day 28 postinfection that cleared parasites from all sites except the brain. Brains of mice killed at different times during infection and after chemotherapy were analyzed, using immunocytochemistry for astrocyte activation and polymerase chain reaction assisted amplification of RNA to detect cytokine transcripts.

RESULTS

Drug-treated animals developed a posttreatment meningoencephalitis similar to that which can occur in humans with late-stage African trypanosomiasis. Between days 14 and 21 postinfection, before chemotherapy and the subsequent development of inflammatory lesions in the brain, astrocytes became activated. The production of several cytokines correlated with this astrocyte activation. Low levels of interleukin-1 alpha transcripts were detected in uninfected controls, but levels increased with astrocyte activation in the infected animals. Transcripts for the macrophage inflammatory protein-1 and tumor necrosis factor-alpha were first detected on day 21 postinfection, with higher levels in mice after development of the posttreatment meningoencephalitis, whereas granulocyte macrophage-colony stimulating factor was detected only in animals that developed posttreatment reaction. Interleukin-6 and interferon-gamma were also first detected on day 21 postinfection, correlating with astrocyte activation but subsequently declined with time in both treated and untreated mice.

CONCLUSIONS

These results indicate that cytokines are being produced within the CNS before any inflammation and that astrocytes may be the source of some of these cytokines. Thus astrocyte activation may be key in the control and development of the CNS inflammatory processes that occur in African sleeping sickness.