Calcineurin Orchestrates Lateral Transfer of Aspergillus fumigatus during Macrophage Cell Death

Abstract

Rationale: Pulmonary aspergillosis is a lethal mold infection in the immunocompromised host. Understanding initial control of infection and how this is altered in the immunocompromised host are key goals for comprehension of the pathogenesis of pulmonary aspergillosis.Objectives: To characterize the outcome of human macrophage infection with Aspergillus fumigatus and how this is altered in transplant recipients on calcineurin inhibitor immunosuppressants. Methods:We defined the outcome of human macrophage infection with A. fumigatus, as well as the impact of calcineurin inhibitors, through a combination of single-cell fluorescence imaging, transcriptomics, proteomics, and in vivo studies.Measurements and Main Results: Macrophage phagocytosis of A. fumigatus enabled control of 90% of fungal germination. However, fungal germination in the late phagosome led to macrophage necrosis. During programmed necroptosis, we observed frequent cell-cell transfer of A. fumigatus between macrophages, which assists subsequent control of germination in recipient macrophages. Lateral transfer occurred through actin-dependent exocytosis of the late endosome in a vasodilator-stimulated phosphoprotein envelope. Its relevance to the control of fungal germination was also shown by direct visualization in our zebrafish aspergillosis model in vivo. The calcineurin inhibitor FK506 (tacrolimus) reduced cell death and lateral transfer in vitro by 50%. This resulted in uncontrolled fungal germination in macrophages and also resulted in hyphal escape.Conclusions: These observations identify programmed, necrosisdependent lateral transfer of A. fumigatus between macrophages as an important host strategy for controlling fungal germination. This process is critically dependent on calcineurin. Our studies provide fundamental insights into the pathogenesis of pulmonary aspergillosis in the immunocompromised host.

Interleukin 1α Is Critical for Resistance against Highly Virulent Aspergillus fumigatus Isolates

“…For C. albicans, it is well established that within the macrophage phagosome, the fungi encounter significant nutrient stress, which must be dealt with in order for the fungi to continue to grow and escape the macrophage (77,78). Interestingly, Shah et al showed that A. fumigatus conidia of the CEA10 strain have the ability to germinate within the late phagosomes of macrophages (79). This germination initiates necroptotic cell death of macrophages, resulting in the lateral transfer of hyphae to other macrophages in order to prevent hyphal escape and maintain control of fungal germination, which is associated with the transcriptional upregulation of Il1a (79).…”

“…Interestingly, Shah et al showed that A. fumigatus conidia of the CEA10 strain have the ability to germinate within the late phagosomes of macrophages (79). This germination initiates necroptotic cell death of macrophages, resulting in the lateral transfer of hyphae to other macrophages in order to prevent hyphal escape and maintain control of fungal germination, which is associated with the transcriptional upregulation of Il1a (79). The metabolic response that enables this growth in A.…”

Real-time visualization of immune cell clearance of Aspergillus fumigatus spores and hyphae

“…Post phagocytosis, melanin inhibits acidification of the phagolysosome by interfering with the translocation of the NADPH oxidase subunit p22 phox , contributing to conidial survival within the phagolysosome (Akoumianaki et al, 2016). Shedding light on macrophage-based mechanisms post-germination in the phagosome, it was shown that A. fumigatus germlings can be passed to a new macrophage to continue inhibition of growth and disease progression (Shah et al, 2016) furthering our understanding of dynamic macrophage interactions with A. fumigatus .…”

Innate Lung Defense during Invasive Aspergillosis: New Mechanisms

“…Alveolar macrophages have long been recognized as effector cells against A. fumigatus . A recent study has shown that this cell type controls the majority of fungal germination [20] . However, some organisms es-cape the late phagosome and are laterally transferred to other macrophages.…”

“…Intriguingly, the calcineurin inhibitor FK506 reduces macrophage death and lateral transfer, which results in uncontrolled fungal germination in macrophages. An additional innate cell type recently studied in A. fumigatus control is the CCR2+ inflammatory monocyte [20]. These cells are thought to function in transporting fungal antigens from the lung to the draining lymph node, where they prime CD4 T cell responses.…”