Extracellular Vesicles from Pneumocystis carinii-infected rats impair fungal viability but are dispensable for macrophage functions

Pneumocystis spp. are host obligate fungal pathogens that can cause severe
pneumonia in mammals and rely heavily on their host for essential
nutrients. The lack of a sustainable in vitro culture system poses
challenges in understanding their metabolism and the acquisition of
essential nutrients from host lungs remains unexplored. Transmission
electron micrographs show Extracellular Vesicles (EVs) are found
near Pneumocystisspp. within the lung. We hypothesized that EVs
transport essential nutrients to the fungi during infection. To
investigate this, EVs from P. carinii- and P. murina-infected rodents were
biochemically and functionally characterized. These EVs contained host
proteins involved in cellular, metabolic, and immune processes as well as
proteins with homologs found in other fungal EV proteomes, indicating
Pneumocystis may release EVs. Notably, EV uptake by P. carinii indicated
their potential involvement in nutrient acquisition and indicated a
possibility for using engineered EVs for efficient therapeutic delivery.
However, EVs added to P. carinii in vitro, did not show increased growth
or viability, implying that additional nutrients or factors are necessary
to support their metabolic requirements. Exposure of macrophages to EVs
increased proinflammatory cytokine levels but did not affect
macrophages' ability to kill or phagocytose P. carinii. These
findings provide vital insights into P. carinii and host EV interactions,
yet the mechanisms underlying P. carinii's survival in the lung
remain uncertain. These studies are the first to isolate, characterize,
and functionally assess EVs from Pneumocystis-infected rodents, promising
to enhance our understanding of host-pathogen dynamics and therapeutic
potential.