Deletion of Plasmodium berghei-specific CD4+ T cells adoptively transferred into recipient mice after challenge with homologous parasite.

The immune response to malaria parasites includes T cell responses that reduce parasites by effector T cell responses and by providing help for antibody responses. Some parasites are more sensitive to antibody and others are more sensitive to cell-mediated immunity. We demonstrate that cultured CD4(+) T cells that produce interferon gamma and interleukin 2, but not interleukin 4, in response to stimulation with the rodent parasite Plasmodium berghei can reduce but not eliminate parasites in vivo after adoptive transfer. Although cells can persist in vivo for up to 9 months in uninfected mice, infection results in elimination of up to 99% of specific T cells in different tissues, as judged by tracking T cells labeled with the fluorescent dye 5-(and -6)-carboxyfluorescein diacetate succinimidyl ester. T cells specific for ovalbumin are unaffected. In vivo activation and division of transferred T cells per se are not responsible for deletion because T cells positive for 5-(and -6)-carboxyfluorescein diacetate succinimidyl ester divide up to six times within 7 days in uninfected mice and are not deleted. Understanding the factors responsible for parasite-mediated specific deletion of T cells would enhance our knowledge of parasite immunity.