MECHANISMS OF IMMUNORESPONSIVENESS AGAINST EMERGING INTRACELLULAR BACTERIA

In this review, the pathogenetic role of emerging intracellular pathog ens is emphasised, especially in the case of immunocompromised hosts s uch as human immunodeficiency virus (HIV)-infected individuals. Furthe rmore, the role of different cytokines (CKs) released by both T helper (h)(1) and Th-2 subsets in the host protection against intracellular pathogens is described. With special reference to CKs produced by macr ophages, the contribution of interleukin (IL)-12 in the regulation of TH1 subset function is pointed out. Particular emphasis is placed on t wo intracellular bacteria, Rhodococcus equi and Bartonella henselae, w hich have the capacity to survive in the host environment. R. equi is a Gram-positive bacterium of veterinary concern, even if, very recentl y, it has been isolated from HIV-infected individuals. On the other ha nd, B. henselae is a Gram-negative bacterium with low endotoxic potenc y which represents the major causative agent of cat scratch disease. H owever, increasing evidence also supports the role of B. henselae as t he aetiological agent of bacillary parenchimal angiomatosis, frequentl y observed in conditions of immunosuppression. Finally, the involvemen t of non-proteinaceous ligands of bacterial origin and/or of exogenous IL-12 in the design of new vaccines against intracellular pathogens i s envisaged.