CCR7 impairs hematopoiesis after hematopoietic stem cell transplantation increasing susceptibility to invasive aspergillosis

Complex genetics architecture contributes to Salmonella resistance in AcB60 mice

Human infection with Salmonella is of global public health concern. In low- and middle-income countries, Salmonella infection is a major source of disease in terms of both mortality and morbidity, while in high-income nations, the pathogen is an ongoing threat to food security. The outcome of infection with Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) in mouse models is dependent upon a coordinated and complex immune response. A panel of recombinant congenic strains (RCS) derived from the reciprocal double backcross of A/J and C57BL/6J mice has been screened for their susceptibility to Salmonella infection, and the RCS AcB60 was identified to be the most resistant strain to Salmonella infection, more resistant than the parental strain A/J. These mice are known to carry resistant alleles at three well-defined Salmonella susceptibility loci, Slc11a1 ^Ity (solute carrier family 11 member 1; Immunity to Typhimurium locus), Pklr ^Ity4 (pyruvate kinase liver and red blood cell; Ity4 locus), and Ity5. In the current study, we used interval mapping to validate a locus on Chr 15, named Ity8, linked to Salmonella resistance in AcB60 mice. Global gene expression analysis during infection identified AcB60-specific expression of genes involved in Ccr7 signaling, including downstream effector Mapk11 (mitogen-activated protein kinase 11), located within the Ity8 interval, and representing a potential positional candidate gene. An additional region on Chr 18 of C57BL/6J descent was shown to be associated with increase resistance in AcB60. These observations provide an opportunity to achieve new insight into the complex genetics of resistance to Salmonella infection in the context of mouse models of human infection with Salmonella Typhimurium.

Mononuclear phagocyte-mediated antifungal immunity: the role of chemotactic receptors and ligands

Over the past two decades, fungal infections have emerged as significant causes of morbidity and mortality in patients with hematological malignancies, hematopoietic stem cell or solid organ transplantation and acquired immunodeficiency syndrome. Besides neutrophils and CD4(+) T lymphocytes, which have long been known to play an indispensable role in promoting protective antifungal immunity, mononuclear phagocytes are now being increasingly recognized as critical mediators of host defense against fungi. Thus, a recent surge of research studies has focused on understanding the mechanisms by which resident and recruited monocytes, macrophages and dendritic cells accumulate and become activated at the sites of fungal infection. Herein, we critically review how a variety of G-protein coupled chemoattractant receptors and their ligands mediate mononuclear phagocyte recruitment and effector function during infection by the most common human fungal pathogens.

Hematopoietic stem cells, infection, and the niche

The immune response to infection is a rapid and multifaceted process. Infection affects homeostasis within the hematopoietic stem cell (HSC) niche, as lost immune cells must be replaced by HSCs. During the immune response, interferon is produced. Surprisingly, HSCs respond directly to interferon, entering the cell cycle from even the most dormant state. The complex response of both the HSCs and the niche to infection is a unique platform on which to consider HSC-niche interactions. Here, we comment on the contribution of the immune system to the niche and on the direct and indirect effect that infection has on HSCs in the niche.

Bayesian development of a dose-response model for Aspergillus fumigatus and invasive aspergillosis

Invasive aspergillosis (IA) is a major cause of mortality in immunocompromized hosts, most often consecutive to the inhalation of spores of Aspergillus. However, the relationship between Aspergillus concentration in the air and probability of IA is not quantitatively known. In this study, this relationship was examined in a murine model of IA. Immunosuppressed Balb/c mice were exposed for 60 minutes at day 0 to an aerosol of A. fumigatus spores (Af293 strain). At day 10, IA was assessed in mice by quantitative culture of the lungs and galactomannan dosage. Fifteen separate nebulizations with varying spore concentrations were performed. Rates of IA ranged from 0% to 100% according to spore concentrations. The dose-response relationship between probability of infection and spore exposure was approximated using the exponential model and the more flexible beta-Poisson model. Prior distributions of the parameters of the models were proposed then updated with data in a Bayesian framework. Both models yielded close median dose-responses of the posterior distributions for the main parameter of the model, but with different dispersions, either when the exposure dose was the concentration in the nebulized suspension or was the estimated quantity of spores inhaled by a mouse during the experiment. The median quantity of inhaled spores that infected 50% of mice was estimated at 1.8 × 10(4) and 3.2 × 10(4) viable spores in the exponential and beta-Poisson models, respectively. This study provides dose-response parameters for quantitative assessment of the relationship between airborne exposure to the reference A. fumigatus strain and probability of IA in immunocompromized hosts.

Immune responses against Aspergillus fumigatus: what have we learned?

PURPOSE OF REVIEW

Aspergillus fumigatus causes invasive and allergenic disease. Host defense relies on the ability of the respiratory immune system to restrict spore germination into invasive hyphae and to limit fungus-induced or inflammation-induced damage in infected tissues. This review covers the molecular and cellular events that mediate innate and CD4 T-cell responses to A. fumigatus and fungal attributes that counter hostile microenvironments and, in turn, affect host responses.

RECENT FINDINGS

Host recognition of fungal cell wall components is critical for fungal uptake, killing, and the formation of protective innate and CD4 T-cell effector populations. Beyond the known role of neutrophils and macrophages, circulating monocytes, dendritic cells, and natural killer cells contribute to optimal defense against A. fumigatus. Genetic and pharmacologic manipulation of A. fumigatus reveals that hypoxia adaptation, cell wall assembly, and secondary metabolite production in mammalian tissues contribute to fungal pathogenesis and the outcome of infection.

SUMMARY

Greater understanding of the immune mechanisms that underlie protective responses and fungal pathways that promote microbial adaptation and growth in mammalian tissue provide a conceptual framework for improving current antifungal therapies.