The Outcome of the Cryptococcus neoformans–Macrophage Interaction Depends on Phagolysosomal Membrane Integrity

Abstract

is a fungal pathogen with worldwide distribution. resides within mature phagolysosomes where it often evades killing and replicates. induces phagolysosomal membrane permeabilization (PMP), but the mechanism for this phenomenon and its consequences for macrophage viability are unknown. In this study, we used flow cytometry methodology in combination with cell viability markers and LysoTracker to measure PMP in J774.16 and murine bone marrow-derived macrophages infected with Our results showed that cells manifesting PMP were positive for apoptotic markers, indicating an association between PMP and apoptosis. We investigated the role of phospholipase B1 in induction of PMP. Macrophages infected with a Δplb1 mutant had reduced PMP compared with those infected with wild-type and phospholipase B1-complemented strains, suggesting a mechanism of action for this virulence factor. Capsular enlargement inside macrophages was identified as an additional likely mechanism for phagolysosomal membrane damage. Macrophages undergoing apoptosis did not maintain an acidic phagolysosomal pH. Induction of PMP with ciprofloxacin enhanced macrophages to trigger lytic exocytosis whereas nonlytic exocytosis was common in those without PMP. Our results suggest that modulation of PMP is a critical event in determining the outcome ofmacrophage interaction.

Integrity under stress: Host membrane remodelling and damage by fungal pathogens

“…Under minimal nutrition, similar to the phagosomal environment, the fungi also metabolise phospholipids containing arachidonic acid, leading to eicosanoid production to suppress phagocytic activity (Wright et al, ). PLB‐deficient strains are less virulent in a murine inhalation model, have reduced ability to penetrate human monolayer cells, and have a profound defect in intracellular growth within host macrophages as well as reduced phagosomal membrane damage (De Leon‐Rodriguez et al, ; R. J. Evans et al, ), which supports the notion that secreted PLB targets both the PM and the phagosomal membrane (Cox et al, ).…”

“…The phagosomal membrane becomes permeable to cytosolic content and the phagosomal lumen alkalinizes (Davis et al, 2015;Tucker & Casadevall, 2002). As the phagosome ruptures, the macrophage also upregulates apoptotic markers (De Leon-Rodriguez et al, 2018). Continued replication of the fungal cells in the cytoplasm eventually results in macrophage lysis (Alvarez & Casadevall, 2006).…”

Pulmonary Iron Limitation Induced by Exogenous Type I IFN Protects Mice from Cryptococcus gattii Independently of T Cells

“…In the lungs, Th1 cells secrete IFN-␥ and other factors that recruit and activate effector macrophages to become fungicidal (22)(23)(24)(25)(26). In vitro polarized M1 macrophages and macrophages harvested from resistant hosts are cryptocidal, whereas in vitro polarized M2 macrophages are permissive (27)(28)(29)(30)(31)(32)(33). Additionally, Th2 T-cell induced M2 polarization may itself be detrimental to the host (34)(35)(36)(37)(38).…”

The capsule ofCryptococcus neoformansmodulates phagosomal pH through its acid-base properties

“…In addition, those glucuronic acid residues can be anticipated to impart considerable acid-base properties to the cryptococcal GXM. In our recent study on the role of phagosomal membrane integrity, we observed that even though apoptotic cells had higher phagolysosomal pH, loss of membrane integrity was not associated with complete loss of acidity, which we hypothesized was due to the acid-based properties of the capsule (14). In contrast, for Candida albicans, which lacks a polysaccharide capsule and hence has no comparable buffering capacity, phagosome permeabilization resulted in luminal alkalinization (19).…”

“…C. neoformans is unusual among intracellular pathogens in that it grows faster at lower pH resulting in faster replication inside phagolysosomes than in the extracellular medium (9). Loss of phagosomal integrity is associated with reduced acidity in that compartment and the triggering of macrophage death (14). Hence, the extent of phagosomal acidification is an important variable, which can favor the microbe or the host cell depending on the state of the interaction (13, 14).…”