THE STEPWISE INTERACTIONS ESTABLISHED BY LEISHMANIA IN ITS HOSTS LES INTERACTIONS PARASITES EUCARYOTES-HÔTES:

Parasitism is based on lasting and renewed interactions between the parasite’s genome and that of the living organism on which it depends for its perpetuation. All parasites subvert and/or remodel the host’s tissue(s) where they live and reproduce. The genus Leishmania is used to illustrate the sequen-tial nature and diversity of the processes occurring in the host. The life cycle of Leishmania requires two successive hosts: hematophagous insects and mammals, the latter also being essential to the sur-vival of the insects. Novel in vivo models were designed to identify and characterise processes estab-lished by Leishmania (L. major) in the tissues (skin and draining lymph nodes) of laboratory mice. Homogenous populations of phagocytic leukocytes (macrophages, dendritic leukocytes, and some-times neutrophils), obtained from laboratory mice, have helped to define how L. amazonensis and L. donovani subverts these leukocytes, respectively as host cells stricto sensu or shuttle cells. The objec-tive of these studies is to improve our understanding of the pathogenesis of the transient skin lesions observed in mammalian hosts, and more importantly, of the conditions required for the perpetua-tion of Leishmania and their transmission from the mammalian host to the female sandfly, acting here as both host and vector