DIFFERENT SUBSETS OF T-CELLS IN CONJUNCTION WITH NATURAL-KILLER-CELLS, MACROPHAGES, AND ACTIVATED MICROGLIA PARTICIPATE IN THE INTRACEREBRAL IMMUNE-RESPONSE TO TOXOPLASMA-GONDII IN ATHYMIC NUDE AND IMMUNOCOMPETENT RATS

Oral infection of athymic nude and immunocompetent Lewis rats with Tox oplasma gondii induced a chronic nonlethal encephalitis. The histopath ological pattern of Toxoplasma encephalitis was significantly differen t in both groups of animals and there were substantially larger number s of Toxoplasma cysts in the brains of athymic rats, Combined immunohi stochemical and flow cytometric analyses of intracerebral leukocytes i dentified alpha beta TCR(+) CD4(+) and CD8(+) T cells, macrophages, an d natural killer cells as inflammatory cell populations in immunocompe tent rats, whereas in athymic mts natural killer cells, macrophages, a nd gamma delta TCR(+) CD8(+) CD3(+) T cells contributed to the intrace rebral inflammatory infiltrates. These findings not only point to a ma jor participation of alpha beta TCR(+) T cells to the intracerebral im mune response, but also indicate that they are not essential to preven t the development of a lethal Toxoplasma encephalitis, In addition, mi croglia were strongly activated in both strains with simultaneous up-r egulation of major histo-compatibility complex class I and II antigens and CD4. Activation of microglia was most prominent in athymic rats, demonstrating that immunodeficiency does not preclude an up-regulation of these molecules including the human immunodeficiency virus recepto r CD4 on microglial cells.