Related Experiment Video
Updated: Apr 3, 2026
Author Spotlight: Advancing Pathogen Detection and Disease Assessment in Real-Time Using M-ROSE
Published on: March 1, 2024
Neither classical nor alternative macrophage activation is required for Pneumocystis clearance during immune
Zhuo-Qian Zhang1, Jing Wang2, Zachary Hoy2
1Department of Microbiology and Immunology, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA.
Abstract:
Pneumocystis is a respiratory fungal pathogen that causes pneumonia (Pneumocystis pneumonia [PcP]) in immunocompromised patients. Alveolar macrophages are critical effectors for CD4(+) T cell-dependent clearance of Pneumocystis, and previous studies found that alternative macrophage activation accelerates fungal clearance during PcP-related immune reconstitution inflammatory syndrome (IRIS). However, the requirement for either classically or alternatively activated macrophages for Pneumocystis clearance has not been determined. Therefore, RAG2(-/-) mice lacking either the interferon gamma (IFN-γ) receptor (IFN-γR) or interleukin 4 receptor alpha (IL-4Rα) were infected with Pneumocystis. These mice were then immune reconstituted with wild-type lymphocytes to preserve the normal T helper response while preventing downstream effects of Th1 or Th2 effector cytokines on macrophage polarization. As expected, RAG2(-/-) mice developed severe disease but effectively cleared Pneumocystis and resolved IRIS. Neither RAG/IFN-γR(-/-) nor RAG/IL-4Rα(-/-) mice displayed impaired Pneumocystis clearance. However, RAG/IFN-γR(-/-) mice developed a dysregulated immune response, with exacerbated IRIS and greater pulmonary function deficits than those in RAG2 and RAG/IL-4Rα(-/-) mice. RAG/IFN-γR(-/-) mice had elevated numbers of lung CD4(+) T cells, neutrophils, eosinophils, and NK cells but severely depressed numbers of lung CD8(+) T suppressor cells. Impaired lung CD8(+) T cell responses in RAG/IFN-γR(-/-) mice were associated with elevated lung IFN-γ levels, and neutralization of IFN-γ restored the CD8 response. These data demonstrate that restricting the ability of macrophages to polarize in response to Th1 or Th2 cytokines does not impair Pneumocystis clearance. However, a cell type-specific IFN-γ/IFN-γR-dependent mechanism regulates CD8(+) T suppressor cell recruitment, limits immunopathogenesis, preserves lung function, and enhances the resolution of PcP-related IRIS.
Insights
Clearance of Pneumocystis pneumonia (PcP) does not require specific macrophage activation. Interferon gamma (IFN-γ) signaling is crucial for regulating CD8(+) T suppressor cells to limit lung inflammation during PcP.
Area of Science:
- Immunology
- Infectious Diseases
- Respiratory Medicine
Background:
- Pneumocystis pneumonia (PcP) is a severe fungal infection in immunocompromised individuals.
- Alveolar macrophages are key for clearing Pneumocystis, with alternative activation linked to improved fungal clearance during immune reconstitution inflammatory syndrome (IRIS).
- The specific roles of classically versus alternatively activated macrophages in Pneumocystis clearance remain unclear.
Purpose of the Study:
- To determine the necessity of classically or alternatively activated macrophages for Pneumocystis clearance.
- To investigate the impact of impaired macrophage polarization on PcP-related IRIS and lung function.
- To elucidate the role of interferon gamma (IFN-γ) in regulating immune responses during PcP.
Main Methods:
- Utilized RAG2(-/-) mice lacking IFN-γ receptor (IFN-γR) or IL-4 receptor alpha (IL-4Rα) for Pneumocystis infection.
- Immune reconstituted these mice with wild-type lymphocytes to maintain T helper responses.
- Analyzed Pneumocystis clearance, IRIS severity, pulmonary function, and immune cell populations (CD4(+), CD8(+), neutrophils, eosinophils, NK cells) in the lungs.
Main Results:
- Pneumocystis clearance and IRIS resolution were not impaired in mice with restricted macrophage polarization (RAG/IFN-γR(-/-) and RAG/IL-4Rα(-/-)).
- RAG/IFN-γR(-/-) mice exhibited dysregulated immune responses, exacerbated IRIS, and worse lung function compared to controls.
- Impaired CD8(+) T suppressor cell numbers in RAG/IFN-γR(-/-) mice correlated with elevated lung IFN-γ; IFN-γ neutralization restored CD8(+) T cell responses.
Conclusions:
- Macrophage polarization flexibility is not essential for clearing Pneumocystis.
- IFN-γ signaling is critical for regulating CD8(+) T suppressor cell recruitment and function.
- IFN-γ-dependent mechanisms are vital for limiting immunopathology, preserving lung function, and resolving PcP-related IRIS.
Related Concept Videos
01:29Pneumonia II: Pathophysiology
01:28Pneumonia IV: Management
Bacterial Pneumonia Treatment
For bacterial pneumonia, antibiotics serve as the cornerstone of therapy. Initial treatment often begins with empirical antibiotics, tailored to the anticipated causative organism and adjusted based on culture results. Key antibiotic choices include:
01:30Pneumonia I: Introduction
Risk Factors
Various factors influence the likelihood of developing pneumonia. Age plays a crucial role, with infants, children under two, and individuals over 65 at increased risk due to their...
01:30Pneumonia III: Complications and Assessment
01:27Chronic Obstructive Pulmonary Disease-IV: Assessement and Diagnostic Studies
Medical History
01:30Pneumonia V: Nursing management and Prevention
The nurse must practice strict medical asepsis and adhere to infection control guidelines to minimize healthcare-associated infections.
Enhance airway patency
Position the patient correctly to facilitate drainage of the affected lung segments. Manual or mechanical percussion and vibration can also be employed....