Although transmissible spongiform encephalopathies (TSE) or prion diseases are neurodegenerative disorders, the immune system is also involved, at least in the early stages of their pathogenesis. Extensive studies have focused on cells targeted by the TSE agent for its replication but few on the possible involvement of macrophages in its clearance, as in more conventional diseases. This review summarises some of the experiments aimed at demonstrating a role for macrophages in TSE and presents the application to TSE of the macrophage "suicide" technique, which has been used to clarify the implication of these cells in the early steps of TSE pathogenesis.