Essential role of extrathymic T cells in protection against malaria

Athymic nude mice carry neither conventional T cells nor NKT cells of thymic origin. However, NK1.1TCRint cells are present in the liver and other immune organs of athymic mice, because these lymphocyte subsets are truly of extrathymic origin. In this study, we examined whether extrathymic T cells had the capability to protect mice from malarial infection. Although B6-nu/nu mice were more sensitive to malaria than control B6 mice, these athymic mice were able to survive malaria when a reduced number of parasitized erythrocytes (5 103 per mouse) were injected. At the fulminant stage, lymphocytosis occurred in the liver and the major expanding lymphocytes were NK1.1TCRint cells (IL-2RTCR). Unconventional CD8 NKT cells (V14) also appeared. Similar to the case of B6 mice, autoantibodies (IgM type) against denatured DNA appeared during malarial infection. Immune lymphocytes isolated from the liver of athymic mice which had recovered from malaria were capable of protecting irradiated euthymic and athymic mice from malaria when cell transfer experiments were conducted. In conjunction with the previous results in euthymic mice, the present results in athymic mice suggest that the major lymphocyte subsets associated with protection against malaria might be extrathymic T cells. The Journal of Immunology, 2002, 169: 301–306. M any investigators still believe that conventional T andB cells are associated with protection against malaria.Therefore, several Ags that are expressed by Plasmo-dium are used for immunization against malaria (1–6). These trials examined the concept of the induction of anti-malaria Abs pro-duced by conventional B cells and the induction of cellular im