Local GM-CSF–Dependent Differentiation and Activation of Pulmonary Dendritic Cells and Macrophages Protect against Progressive Cryptococcal Lung Infection in Mice

Abstract

Patients with acquired deficiency in granulocyte macrophage colony stimulating factor (GM-CSF) are susceptible to infections with Cryptococcus (C.) neoformans and other opportunistic fungi. We previously showed that GM-CSF protects against progressive fungal disease using a murine model of cryptococcal lung infection. To better understand the cellular and molecular mechanisms through which GM-CSF enhances anti-fungal host defenses, we investigated temporal and spatial relationships between myeloid and lymphoid immune responses in GM+/+ and GM−/− mice infected with a moderately-virulent encapsulated strain of C. neoformans (strain 52D). Our data demonstrate that GM-CSF deficiency led to a reduction in: 1) total lung leukocyte recruitment; 2) Th2 and Th17 responses; 3) total numbers of CD11b+ dendritic cells (DC), and CD11b− and CD11b+ macrophages (Mϕ); 4) DC and Mϕ activation; and 5) localization of DC and Mϕ to the microanatomic sites of alveolar infection. In contrast, GM-CSF deficiency resulted in increased accumulation of DC and Mϕ precursors, namely Ly-6Chigh monocytes, in the blood and lungs of infected mice. Collectively, these results show that GM-CSF promotes the local differentiation, accumulation, activation, and alveolar localization of lung DC and macrophages in mice with cryptococcal lung infection. These findings identify GM-CSF as central to the protective immune response that prevents progressive fungal disease and thus shed new light on the increased susceptibility to these infections observed in patients with acquired GM-CSF deficiency.

Autoantibody-Mediated Pulmonary Alveolar Proteinosis in Rasgrp1-Deficient Mice

“…(data not shown); 2) aged Rasgrp1 -deficient mice that do not develop PAP pathology are frequently caged with aged Rasgrp1 -deficient mice that develop PAP pathology; and 3) SP-B levels are decreased in a mouse model of secondary PAP 48 whereas SP-B expression is unchanged in aged Rasgrp1 -deficient mice in comparison to control mice. It is more likely that autoantibody neutralization of GM-CSF contributes to impaired clearance by alveolar macrophages 6 and/or inhibition of pulmonary macrophage and dendritic cell maturation 7, 49 . Future studies can elucidate whether fungal infections in aged Rasgrp1 -deficient mice contribute to mortality since GM-CSF-deficient mice exhibit a normal lifespan 1 .…”

Calcineurin Orchestrates Lateral Transfer of Aspergillus fumigatus during Macrophage Cell Death

“…Normally inhaled conidia are cleared by alveolar macrophages to prevent fungal germination, tissue invasion, and destructive lung disease (2,3). Our previous work with murine and zebrafish models of invasive aspergillosis showed the importance of macrophages in control of Af early postinfection, with neutrophil influx as a later event (4,5).…”

Anti–PD-1 Antibody Treatment Promotes Clearance of Persistent Cryptococcal Lung Infection in Mice

“…Specific subsets of lung dendritic cells and macrophages were identified within lung leukocyte populations obtained at 0, 2, 3, and 4 WPI using flow cytometric analysis and a detailed gating scheme (refer to (8, 41, 42) and Figure 3A–F). Results demonstrated a significant 2-fold increase in the number of lung neutrophils present at 4 WPI, and a significant 10- to 15-fold increase in the number of eosinophils present at all time-points post-infection (Figure 3G).…”

“…Persistent cryptococcal lung infection, effectively modeled by intratracheal inoculation of C57BL/6 mice with a moderately virulent strain of C. neoformans (52D), is characterized by a mixed T helper (Th) polarization immunophenotype, which contains but does not eliminate the fungus (8–12). Persistent lung infection reflects an immune balance between concurrent induction of interferon gamma (IFNγ) and interleukin 17 (IL-17), which promote classical (M1) macrophage activation and fungal killing (13–16), with expression of IL-4, IL-13 and IL-10 which promote alternative (M2) macrophage activation and intracellular fungal survival (9, 15, 17).…”

“…A study by Guerrero et al demonstrated that infection with more virulent, mucoid colonies of C. neoformans is associated with increased expression of PD-L1 and PD-L2 by alveolar macrophages (33). We have recently shown that GM-CSF promotes PD-L2 expression by dendritic cells (DCs) in the lungs of mice with persistent cryptococcal lung infection (8). Neither study provided a detailed evaluation of this pathway throughout infection or assessed the therapeutic effects of PD-1 blockade.…”