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Updated: Mar 25, 2026
Size Matters: Measurement of Capsule Diameter in Cryptococcus neoformans
Published on: February 27, 2018
Cryptococcus neoformans Intracellular Proliferation and Capsule Size Determines Early Macrophage Control of Infection
Aleksandra Bojarczuk1,2, Katie A Miller1,2, Richard Hotham1,2
1Department of Infection, Immunity and Cardiovascular Disease, Medical School, University of Sheffield, Sheffield, UK.
Abstract:
Cryptococcus neoformans is a significant fungal pathogen of immunocompromised patients. Many questions remain regarding the function of macrophages in normal clearance of cryptococcal infection and the defects present in uncontrolled cryptococcosis. Two current limitations are: 1) The difficulties in interpreting studies using isolated macrophages in the context of the progression of infection, and 2) The use of high resolution imaging in understanding immune cell behavior during animal infection. Here we describe a high-content imaging method in a zebrafish model of cryptococcosis that permits the detailed analysis of macrophage interactions with C. neoformans during infection. Using this approach we demonstrate that, while macrophages are critical for control of C. neoformans, a failure of macrophage response is not the limiting defect in fatal infections. We find phagocytosis is restrained very early in infection and that increases in cryptococcal number are driven by intracellular proliferation. We show that macrophages preferentially phagocytose cryptococci with smaller polysaccharide capsules and that capsule size is greatly increased over twenty-four hours of infection, a change that is sufficient to severely limit further phagocytosis. Thus, high-content imaging of cryptococcal infection in vivo demonstrates how very early interactions between macrophages and cryptococci are critical in the outcome of cryptococcosis.
Insights
Macrophages are crucial for controlling fungal infections like cryptococcosis. However, early limitations in phagocytosis, not macrophage failure, drive fatal outcomes in cryptococcal infections.
Area of Science:
- Immunology
- Mycology
- Infectious Diseases
Background:
- Cryptococcus neoformans is a major fungal pathogen affecting immunocompromised individuals.
- Understanding macrophage roles in cryptococcal infection clearance and defects in uncontrolled cases remains challenging.
- Current research faces limitations in applying in vitro macrophage studies to in vivo infection progression and in utilizing high-resolution imaging for immune cell behavior analysis during animal infections.
Purpose of the Study:
- To develop and utilize a high-content imaging method in a zebrafish model for detailed analysis of macrophage interactions with Cryptococcus neoformans during infection.
- To investigate the functional role of macrophages in controlling cryptococcal infections and identify defects contributing to uncontrolled cryptococcosis.
Main Methods:
- Development of a high-content imaging technique.
- Application of the technique in a zebrafish model of cryptococcosis.
- Detailed analysis of macrophage-Cryptococcus neoformans interactions in vivo.
Main Results:
- Macrophages are critical for controlling C. neoformans, but their response failure is not the primary defect in fatal infections.
- Phagocytosis is significantly limited early in infection, with cryptococcal proliferation driving increased numbers.
- Macrophages preferentially phagocytose C. neoformans with smaller polysaccharide capsules.
- Capsule size increases substantially within 24 hours, severely restricting further phagocytosis.
Conclusions:
- High-content imaging in a zebrafish model provides critical insights into cryptococcosis pathogenesis.
- Early interactions between macrophages and C. neoformans, particularly capsule size, are pivotal in determining infection outcomes.
- Intracellular proliferation and capsule growth, rather than solely macrophage defects, are key drivers of uncontrolled cryptococcosis.
