In vitro induction of nitric oxide synthase in astrocytes and microglia by Trypanosoma brucei brucei

In stage II human african trypanosomiasis (HAT), which is characterized by central nervous system (CNS) involvement, neurones and oligodendrocytes might be targets of dysimmune processes. Nitric oxide (NO) production by peripheral macrophages is documented in HAT. We studied the production of NO by murine astrocytes and microglia cocultured with Trypanosoma brucei (T. b.) brucei AnTat 1.9. Purified astrocytes or microglia from mouse brains were cocultured with T. b. brucei, and in some instances with interferon (IFN)-gamma, which is known to be released during the disease and also to be a growth factor for trypanosomes. Inducible NO synthase (iNOS) expression was studied by indirect immunofluorescence and reverse transcriptase-polymerase chain reaction. NO production was determined by measuring nitrite generation in culture. Detection of iNOS in astrocytes and microglia in the presence of T. b. brucei, was closely associated with nitrite production and was strongly enhanced by the addition of IFN-gamma to the culture medium. The stimulation of iNOS activity required parasite-cell contact and likely occurred at the transcriptional level. This study demonstrates the induction of iNOS in CNS-related macrophage cells in the presence of trypanosomes and its potentiation by IFN-gamma.