Targets as the malarial infection and the attack of extrathymic T cells : MHC^+ erytherocytes in the bone marrow

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Mice were infected with Plasmodium(P.)yoelii, blood-stage parasites. Both the liver and spleen were the sites of inflammation during malarial infection at the beginning of day 7. The major expanding cells were found to be NK1.1 intermediate αβTCR(αβTCR^<int>)in the liver and spleen, although the population of NK1.1^+αβTCR^<int> cells remained constant or slightly increased. These TCR^<int> cells are of extrathymic origin or are generated by an alternative intrathymic pathway, and are distinguished from conventional T cells of thymic origin. During malarial infection, the population of conventional T cells did not increase at all. TCR^<int> cells purified from the liver of mice which had recovered from P.yoelii infection protected mice from malaria when they were transferred into 6.5 Gy-irradiated mice. Interestingly, the immunity against malaria seemed to disappear as a function of time after the recovery. Namely, mice which had recovered from malaria one year previously again became susceptible to malarial infection. The present results suggest that TCR^<int> cells are intimately associated with the protection against malarial infection and, therefore, that the mice which had recovered from malaria one year previously lost such immunity.