The pathogenesis of mycobacterial infection is associated with an ability to interfere with maturation of the phagosomal compartment after ingestion by macrophages. Identification of the mycobacterial components that contribute to this phenomenon will allow rational design of novel approaches to the treatment and prevention of tuberculosis. Microarray-based screening of a transposon library was used to identify mutations that influence the fate of Mycobacterium bovis bacille Calmette-Guérin (BCG) following uptake by macrophages. A screen based on bacterial survival during a 3-d infection highlighted genes previously implicated in growth of Mycobacterium tuberculosis in macrophages and in mice, together with a number of other virulence genes including a locus encoding virulence-associated membrane proteins and a series of transporter molecules. A second screen based on separation of acidified and non-acidified phagosomes by flow cytometry identified genes involved in mycobacterial control of early acidification. This included the KefB potassium/proton antiport. Mutants unable to control early acidification were significantly attenuated for growth during 6-d infections of macrophages. Early acidification of the phagosome is associated with reduced survival of BCG in macrophages. A strong correlation exists between genes required for intracellular survival of BCG and those required for growth of M. tuberculosis in mice. In contrast, very little correlation exists between genes required for intracellular survival of BCG and those that are up-regulated during intracellular adaptation of M. tuberculosis. This study has identified targets for interventions to promote immune clearance of tuberculosis infection. The screening technologies demonstrated in this study will be useful to the study of pathogenesis in many other intracellular microorganisms.
Although the relationship between hematopoietic stem cells and progenitor populations has been investigated extensively under steady-state conditions, the dynamic response of the hematopoietic compartment during acute infection is largely unknown. Here we show that after infection of mice with Plasmodium chabaudi, a c-Kit(hi) progenitor subset positive for interleukin 7 receptor-alpha (IL-7Ralpha) emerged that had both lymphoid and myeloid potential in vitro. After being transferred into uninfected alymphoid or malaria-infected hosts, IL-7Ralpha(+)c-Kit(hi) progenitors generated mainly myeloid cells that contributed to the clearance of infected erythrocytes in infected hosts. The generation of these infection-induced progenitors was critically dependent on interferon-gamma (IFN-gamma) signaling in hematopoietic progenitors. Thus, IFN-gamma is a key modulator of hematopoiesis and innate and adaptive immunity during acute malaria infection.
Plasmacytoid dendritic cells (pcDC) and myeloid dendritic cells (myDC) are shown to express CD4 and low levels of CCR5 and CXCR4, but only myDC express DC SIGN, a C-type lectin that binds human immunodeficiency virus but does not mediate virus entry. Both DC types were more susceptible to infection with a macrophage than a lymphotropic strain of human immunodeficiency virus type 1, but pcDC were more readily infected than myDC.
Three influenza virus pandemics occurred in the last century, in 1918 killing 40-50 million people. In the absence of strain-specific vaccines, with potential resistance to antivirals and the threat of an imminent pandemic, strategies that alleviate symptoms are a priority. Reactive oxygen species are potent antimicrobial agents but cause immunopathology when produced in excess. Mice lacking a functional phagocyte NADPH oxidase (Cybb tm1 mice) or treated with the metalloporphyrin antioxidant manganese (III) tetrakis (N-ethyl pyridinium-2-yl) porpyhrin (MnTE-2-PyP) show heightened inflammatory infiltrates in their airways in response to pulmonary influenza infection, with augmented macrophage populations and a Th1-skewed T cell infiltrate. Underlying this exuberant macrophage response was a significant reduction in apoptosis and down-regulation of the myeloid inhibitory molecule CD200. Both, Cybb tm1 and MnTE-2-PyP-treated mice exhibited a reduced influenza titer in the lung parenchyma. Inflammatory infiltrate into the lung parenchyma was markedly reduced and lung function significantly improved. Manipulation of the homeostatic control of myeloid cells by inflammatory mediators therefore represents a novel therapeutic strategy in the treatment of influenza virus infection.
Respiratory infections are the third leading cause of death worldwide. Illness is caused by pathogen replication and disruption of airway homeostasis by excessive expansion of cell numbers. One strategy to prevent lung immune–mediated damage involves reducing the cellular burden. To date, antiinflammatory strategies have affected both antigen-specific and naive immune repertoires. Here we report a novel form of immune intervention that specifically targets recently activated T cells alone. OX40 (CD134) is absent on naive T cells but up-regulated 1–2 d after antigen activation. OX40–immunoglobulin fusion proteins block the interaction of OX40 with its ligand on antigen-presenting cells and eliminate weight loss and cachexia without preventing virus clearance. Reduced proliferation and enhanced apoptosis of lung cells accompanied the improved clinical phenotype. Manipulation of this late costimulatory pathway has clear therapeutic potential for the treatment of dysregulated lung immune responses.
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