Extracellular vesicles of Emergomyces africanus modulate host immune responses and reflect metabolic adaptations to nutrient availability

TL;DR

This study shows how a fungus called Emergomyces africanus uses tiny particles to change immune responses and survive in the host, depending on nutrient availability.

Contribution

The study reveals how E. africanus adjusts extracellular vesicle content under different nutrient conditions to modulate immune responses and enhance survival.

Findings

EVs under nutrient limitation carry virulence proteins like catalase and HSP60, activating dendritic cells and promoting inflammation.

BMDMs exposed to these EVs showed increased IL-10 and improved antifungal activity against E. africanus.

EV pre-treatment protected Galleria mellonella against Histoplasma capsulatum infection.

Abstract

Emergomyces africanus is a thermal dimorphic fungus and a leading cause of emergomycosis, a neglected infection primarily affecting immunocompromised individuals. Despite its clinical relevance, little is known about how E. africanus adapts to the host environment. Recent studies suggest that fungal extracellular vesicles (EVs) may contribute to host adaptation by modulating immune responses and transporting virulence factors. Here, we report the production and characterization of E. africanus EVs obtained under nutrient-rich and nutrient-limited media, mimicking environmental and host-like conditions. We also evaluated the effect of E. africanus EVs released in nutrient-limited media on bone marrow-derived dendritic cells (BMDCs) and bone marrow-derived macrophages (BMDMs). Under nutrient limitation, E. africanus released EVs enriched in virulence-associated proteins, including catalase, HSP60, and chitinase, whereas EVs from rich media carried proteins linked to anabolic pathways. Chitin-like structures and β-1,3-glucans were also detected in EVs released in nutrient-limited conditions. EVs from nutrient-limited conditions activated BMDCs, increased MHC-II and CD40 expression, and promoted a pro-inflammatory cytokine profile (IL-6 and TNF-α). In contrast, BMDMs exhibited elevated IL-10 levels, suggesting an anti-inflammatory phenotype. Remarkably, EV pre-treatment enhanced BMDM antifungal activity, significantly reducing E. africanus viability post-infection. These findings show that E. africanus dynamically adjusts its EV cargo in response to environmental cues, directly influencing immune modulation and fungal survival. Indeed, pre-treatment of the insect Galleria mellonella with EVs induced a protective response against a lethal inoculum of Histoplasma capsulatum. This work provides new insights into fungal adaptation and highlights EVs as potential therapeutic and vaccine platforms.

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