GAMMA-DELTA T-CELLS CONTRIBUTE TO IMMUNITY AGAINST THE LIVER STAGES OF MALARIA IN ALPHA-BETA T-CELL-DEFICIENT MICE

The functional role of gammadelta T cells (expressing the gammadelta heterodimeric T-cell receptor for antigen) in infectious diseases remains largely unknown. We have therefore attempted to define the possible role of these T cells in the immune response against the various developmental stages of malaria parasites. For this purpose, we monitored the immune response and the development of liver and blood stages of Plasmodium yoelii, a rodent malaria parasite, in immunized and nonimmunized alphabeta T-cell-deficient and gammadelta T-cell-deficient mice. Immunization of alphabeta T-cell-deficient mice with irradiated sporozoites induced an immune response that significantly inhibited the development of the parasite's liver stages. This inhibitory immune response was abolished by an antibody-mediated transient in vivo depletion of gammadelta T cells. Two gammadelta T-cell clones were derived from malaria-immunized alphabeta T-cell-deficient mice. The adoptive transfer of one of these gammadelta T-cell clones to normal mice inhibited the development of liver stages, following sporozoite inoculation. These results provide evidence for gammadelta T-cell-mediated protective immunity against parasites, in the absence of alphabeta T cells. As for the blood phase of the infection, both normal mice and gammadelta T-cell-deficient mice cleared the blood stages of the nonlethal strain of P. yoelii, while alphabeta T-cell-deficient mice failed to control the parasitemia.