The capsule of Cryptococcus neoformans is its dominant virulence factor and plays a key role in the biology of this fungus. In this essay, we focus on the capsule as a cellular structure and note the limitations inherent in the current methodologies available for its study. Given that no single method can provide the structure of the capsule, our notions of what is the cryptococcal capsule must be arrived at by synthesizing information gathered from very different methodological approaches including microscopy, polysaccharide chemistry and physical chemistry of macromolecules. The emerging picture is one of a carefully regulated dynamic structure that is constantly rearranged as a response to environmental stimulation and cellular replication. In the environment, the capsule protects the fungus against desiccation and phagocytic predators. In animal hosts the capsule functions in both offensive and defensive modes, such that it interferes with immune responses while providing the fungal cell with a defensive shield that is both antiphagocytic and capable of absorbing microbicidal oxidative bursts from phagocytic cells. Finally, we delineate a set of unsolved problems in the cryptococcal capsule field that could provide fertile ground for future investigations.

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.

Cryptococcus neoformans is a pathogenic yeast capable of a unique and intriguing form of cell-to-cell transfer between macrophage cells. The mechanism for cell-to-cell transfer is not understood. In this study, we imaged mouse macrophages with CellTracker Green 5-chloromethylfluorescein diacetate–labeled cytosol to ascertain whether cytosol was shared between donor and acceptor macrophages. Analysis of several transfer events detected no transfer of cytosol from donor-to-acceptor mouse macrophages. However, blocking Fc and complement receptors resulted in a major diminution of cell-to-cell transfer events. The timing of cell-to-cell transfer (11.17 min) closely approximated the sum of phagocytosis (4.18 min) and exocytosis (6.71 min) times. We propose that macrophage cell-to-cell transfer represents a nonlytic exocytosis event, followed by phagocytosis into a macrophage that is in close proximity, and name this process Dragotcytosis (“Dragot” is a Greek surname meaning “sentinel”), as it represents sharing of a microbe between two sentinel cells of the innate immune system.

Background. The US Food and Drug Administration authorized Convalescent Plasma (CCP) therapy for hospitalized COVID-19 patients via the Expanded Access Program (EAP) and the Emergency Use Authorization (EUA), leading to use in about 500,000 patients during the first year of the pandemic for the US.Methods. We tracked the number of CCP units dispensed to hospitals by blood banking organizations and correlated that usage with hospital admission and mortality data.Results. CCP usage per admission peaked in Fall 2020, with more than 40% of inpatients estimated to have received CCP between late September and early November 2020. However, after randomized controlled trials failed to show a reduction in mortality, CCP usage per admission declined steadily to a nadir of less than 10% in March 2021. We found a strong inverse correlation (r = -0.52, P = 0.002) between CCP usage per hospital admission and deaths occurring two weeks after admission, and this finding was robust to examination of deaths taking place one, two or three weeks after admission. Changes in the number of hospital admissions, SARS-CoV-2 variants, and age of patients could not explain these findings. The retreat from CCP usage might have resulted in as many as 29,000 excess deaths from mid-November 2020 to February 2021.Conclusions. A strong inverse correlation between CCP use and mortality per admission in the USA provides population level evidence consistent with the notion that CCP reduces mortality in COVID-19 and suggests that the recent decline in usage could have resulted in excess deaths.Funding. There was no specific funding for this study. AC was supported in part by RO1 HL059842 and R01 AI1520789; MJJ was supported in part by 5R35HL139854. This project has been funded in whole or in part with Federal funds from the Department of Health and Human Services; Office of the Assistant Secretary for Preparedness and Response; Biomedical Advanced Research and Development Authority under Contract No. 75A50120C00096.

No abstract