Interferon-γ and T-bet expression in a patient with toxoplasmic lymphadenopathy

Infection with Toxoplasma gondii (TG) presents in some individuals as a self-limited disease with a predominant lymphadenopathy characterized by prominent B-cell activation. As this is in contrast to the in vitro based concept of a Th1-immune response against TG, we investigated native lymphoid tissue and peripheral blood of a patient with serologic evidence of toxoplasmosis to verify which cells show Th1-response features. High-level expression of T-bet in monocytoid B-cells, in germinal center B-cells, and in a lesser amount in T cells could be demonstrated by immunohistochemistry. In vitro stimulation of lymph node cells with either TG, staphylococcus enterotoxin B, or phorbol 12-myristate 13-acetate/ionomycin revealed an interferon-γ expression in T-bet+ B cells only in the patient and not in controls. Similar results were found for T-bet+ T cells which were also present in controls. CD4+ peripheral blood cells stimulated with TG antigens showed a TG-specific but attenuated Th1-reactivity in the patient associated with a reduced expression of IL-2 when compared with controls. We conclude that the pathogenesis and course of toxoplasmic lymphadenopathy is based on a Th1-cell defect, which becomes compensated by the B cells mounting a Th1-like immune response.