A HYPOTHESIS ABOUT THE CHRONICITY OF MALARIA INFECTION

It is generally accepted that malaria evolves as a chronic blood infec tion by escaping the immune responses directed against a series of ant igens that express variable epitopes and/or by selecting parasite popu lations with distinct polymorphic antigens. However, exacting in vitro studies, performed with clinically well-defined biological material, have correlated the state of protection of African adults (in whom low -grade infection persists) with an indirect defence mechanism where th e antibodies are effective owing to their ability to cooperate with bl ood monocytes. Further studies showed that the antibody bridges the pa rasite (at the merozoite stage) with a monocyte and triggers the relea se of mediators which have a parasitistatic, reversible and non-antige n-specific effect. The fact that the parasite directly triggers the an tiparasite effect lends Pierre Druilhe and Jean-Louis Perignon to form ulate here an alternative hypothesis for the chronicity of malaria inf ection, which would rely on conserved antigenic targets and, in contra st with direct mechanisms, would not select emerging mutated parasites . The above two mechanisms are discussed in the context of their fitne ss with clinical and parasitological observations. It is proposed that they are not mutually exclusive but, rather, may come into play succe ssively as patients gradually evolve from high-gr ade symptomatic to I o iu-grade asymptomatic parasitic infection.