Immune mimicry in malaria: Plasmodium falciparum secretes a functional histamine-releasing factor homolog in vitro and in vivo

The Plasmodium falciparum translationally controlled tumor protein (TCTP) i s a homolog of the mammalian histamine-releasing factor (HRF), which causes histamine release from human basophils and IL-8 secretion from eosinophils . Histamine, IL-8, and eosinophils have been reported to be elevated in pat ients with malaria. This study was undertaken to determine whether malarial TCTP is found in the plasma of malaria-infected patients and to determine whether it has HRF biologic activity. Malarial TCTP was found in lightly in fected human volunteers and in heavily infected Malawian children, but not in uninfected patients. Recombinant malarial TCTP, like HRF, stimulated his tamine release from basophils and IL-8 secretion from eosinophils in vitro. Whereas malarial TCTP was less active than HRF, the concentrations that we re effective in vitro could be achievable in vivo. These data suggest that malarial TCTP, present in human plasma during a malarial illness, may affec t host immune responses in vivo.