Phosphodiesterase-4 Inhibition Alters Gene Expression and Improves Isoniazid – Mediated Clearance of Mycobacterium tuberculosis in Rabbit Lungs

Tuberculosis (TB) treatment is hampered by the long duration of antibiotic therapy required to achieve cure. This indolent response has been partly attributed to the ability of subpopulations of less metabolically active Mycobacterium tuberculosis (Mtb) to withstand killing by current anti-TB drugs. We have used immune modulation with a phosphodiesterase-4 (PDE4) inhibitor, CC-3052, that reduces tumor necrosis factor alpha (TNF-α) production by increasing intracellular cAMP in macrophages, to examine the crosstalk between host and pathogen in rabbits with pulmonary TB during treatment with isoniazid (INH). Based on DNA microarray, changes in host gene expression during CC-3052 treatment of Mtb infected rabbits support a link between PDE4 inhibition and specific down-regulation of the innate immune response. The overall pattern of host gene expression in the lungs of infected rabbits treated with CC-3052, compared to untreated rabbits, was similar to that described in vitro in resting Mtb infected macrophages, suggesting suboptimal macrophage activation. These alterations in host immunity were associated with corresponding down-regulation of a number of Mtb genes that have been associated with a metabolic shift towards dormancy. Moreover, treatment with CC-3052 and INH resulted in reduced expression of those genes associated with the bacterial response to INH. Importantly, CC-3052 treatment of infected rabbits was associated with reduced ability of Mtb to withstand INH killing, shown by improved bacillary clearance, from the lungs of co-treated animals compared to rabbits treated with INH alone. The results of our study suggest that changes in Mtb gene expression, in response to changes in the host immune response, can alter the responsiveness of the bacteria to antimicrobial agents. These findings provide a basis for exploring the potential use of adjunctive immune modulation with PDE4 inhibitors to enhance the efficacy of existing anti-TB treatment

A defective Th1 response of the spleen in the initial phase may explain why splenectomy helps prevent a Listeria infection

Listeria monocytogenes (Listeria) are known to grow and proliferate in the liver while a splenectomy induces host resistance against a Listeria infection despite the fact that a splenectomy inhibits the Th1 response. Therefore, the mechanism by which a splenectomy helps to prevent the growth of Listeria still remains to be elucidated. After an i.v. challenge of Listeria (1 × 10(6) CFU) in C57BL/6 mice, Listeria rapidly increased in the spleen but not in the liver until 48 h. However, after this initial phase, Listeria remarkably grew in the liver. In contrast, when the mice received a splenectomy beforehand, no remarkable growth of Listeria in the liver was observed after Listeria challenge despite the fact that serum IFN-γ and IL-12 levels at 24 h after Listeria challenge were significantly lower than those in the sham mice. However, the liver leucocytes from mice by 6 h after infection produced a substantial amount of IFN-γ while spleen MNC did not, whereas spleen leucocytes at 24 h after Listeria challenge did. Consistently, the IFN-γ and IL-12 levels in the tissue homogenates of the spleen were significantly lower than in those of the liver until 6 h after infection. This defective spleen Th1 response in the early phase of Listeria infection was corrected by an IL-18 i.p. injection just after the Listeria challenge. Our findings suggest that Listeria exploit the defective Th1 environment of the spleen in the initial phase and afterwards overcome the host defense mechanism of the liver

Mechanism involved in phagocytosis and killing of Listeria monocytogenes by Acanthamoeba polyphaga

© Springer-Verlag 2009Intra-cellular pathogen, Listeria monocytogenes, is capable of invasion and survival within mammalian cells. However, Acanthamoeba polyphaga trophozoites phagocytose and rapidly degrade Listeria cells. In order to provide more information on amoeba phagocytosis and killing mechanisms, this study used several inhibitor agents known to affect the phagocytosis and killing of bacteria by eukaryotes. Amoebae were pre-treated with mannose, cytochalasin D, wortmannin, suramin, ammonium chloride, bafilomycin A and monensin followed by co-culture with bacteria. Phagocytosis and killing of bacterial cells by amoeba trophozoites was assessed using plate counting methods and microscopy. The data presented indicates that actin polymerisation and cytoskeletal rearrangement are involved in phagocytosis of L. monocytogenes cells by A. polyphaga trophozoites. Further, both phagosomal acidification and phagosome–lysosome fusion are involved in killing and degradation of L. monocytogenes cells by A. polyphaga. However, the mannose-binding protein receptor does not play an important role in uptake of bacteria by amoeba trophozoites. In conclusion, this data reveals the similar principles of molecular mechanisms used by different types of eukaryotes in uptake and killing of bacteria.Alisha Akya, Andrew Pointon and Connor Thoma