Many intracellular pathogens infect macrophages and these pathogens require iron for growth. Here we demonstrate in vitro that the intracellular growth of Chlamydia psittaci, trachomatis, and Legionella pneumophila is regulated by the levels of intracellular iron. Macrophages that express cell surface ferroportin, the only known cellular iron exporter, limit the intracellular growth of these bacteria.Hepcidin is an antimicrobial peptide secreted by the liver in response to inflammation. Hepcidin binds to ferroportin mediating its internalization and degradation. Addition of hepcidin to infected macrophages enhanced the intracellular growth of these pathogens. Macrophages from flatiron mice, a strain heterozygous for a loss-of-function ferroportin mutation, showed enhanced intracellular bacterial growth independent of the presence of exogenous hepcidin. Macrophages, from wild-type or flatiron mice, incubated with the oral iron chelator deferriprone or desferasirox showed reduced intracellular bacterial growth suggesting that these chelators might be therapeutic in chronic intracellular bacterial infections. (Blood. 2008;112:866-874) IntroductionHypoferremia is a hallmark of inflammation and results from increased secretion of the liver hormone hepcidin (for review, see Nemeth and Ganz 1 ). Hepcidin is secreted by hepatocytes in response to inflammatory stimuli, notably interleuklin-6 (IL-6). [2][3][4] Hepcidin binds to the iron exporter ferroportin (Fpn), leading to its internalization and degradation. 5 Fpn is the only identified cellular iron exporter and is present on macrophages, absorptive enterocytes, and placenta. Loss of cell surface Fpn results in hypoferremia, which, if persistent, leads to iron-limited erythropoiesis. 6 The hypoferremia of inflammation is thought to represent an antibacterial defense response, as iron acquisition proteins are virulence factors for many species of bacteria. 7 The loss of cell surface Fpn also leads to increased cellular iron, particularly in macrophages that are continuously obtaining iron from senescent red blood cells. The hypoferremia of inflammation may limit the growth of extracellular bacteria but may promote the growth of intracellular bacteria. Support for this hypothesis has been suggested by studies in Salmonellainfected macrophages, where addition of hepcidin promoted the growth of bacteria. 8,9 We show that the growth of 3 other species of intracellular bacteria, Chlamydia psittaci, C trachomatis, and Legionella pneumophila, is promoted by hepcidin-mediated down-regulation of Fpn. Chlamydia spp are obligate intracellular pathogens that have a unique developmental cycle. The infectious forms of Chlamydia spp are termed elementary bodies. After infecting host cells, the elementary bodies differentiate (2-4 hours) within the inclusion membrane to the metabolically active bacteria, termed reticulate bodies, which are noninfectious. The reticulate bodies replicate within the expanding inclusion membrane for approximately 2 to 3 days, differentiate back to element...

Chediak-Higashi Syndrome is an autosomal recessive disorder that affects vesicle morphology. The Chs1/Lyst protein is a member of the BEACH family of proteins. The absence of Chs1/Lyst gives rise to enlarged lysosomes. Lysosome size is regulated by a balance between vesicle fusion and fission and can be reversibly altered by acidifying the cytoplasm using Acetate Ringer’s or by incubating with the drug vacuolin-1. We took advantage of these procedures to determine rates of lysosome fusion and fission in the presence or absence of Chs1/Lyst. Here we show by microscopy, flow cytometry and in vitro fusion that the absence of the Chs1/Lyst protein does not increase the rate of lysosome fusion. Rather, our data indicate that loss of this protein decreases the rate of lysosome fission. We further show that overexpression of the Chs1/Lyst protein gives rise to a faster rate of lysosome fission. These results indicate that Chs1/Lyst regulates lysosome size by affecting fission.