Association of intermediate T cell receptor cells, mainly their NK1.1(-) subset, with protection from malaria

Mice were infected with Plasmodium (P.) yoelii blood-stage parasites. Both the liver and spleen were the sites of inflammation during malarial infecti on at the beginning of day 7, The major expanding cells were found to be NK 1.1(-) intermediate alpha beta TCR (alpha beta TCRint) in the liver and spl een, although the population of NK1.1(+) alpha beta TCRint cells remained c onstant or slightly increased. These TCRint cells are of extrathymic origin or are generated by an alternative intrathymic pathway and are distinguish ed from conventional T cells of thymic origin. During malarial infection, t he population of conventional T cells did not increase at all. TCRint cells purified from the liver of mice which had recovered from P, yoelii infecti on protected mice from malaria when they were transferred into 6.5-Gy-irrad iated mice. Interestingly, the immunity against malaria seemed to disappear as a function of time after recovery, namely, mice which had recovered fro m malaria 1 year previously again became susceptible to malarial infection, The present results suggest that TCRint cells are intimately associated wi th protection against malarial infection and, therefore, that mice which ha d recovered from malaria 1 year previously lost such immunity, (C) 2001 Aca demic Press.