The C3–C3aR axis modulates trained immunity in alveolar macrophages
9 affiliations
- 1Divisions of Pulmonary and Critical Care Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- 2Washington University School of Medicine
- 3Departments of Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- 4University of California-Los Angeles
- 5Lung Imaging Laboratory, Division of Pulmonary, Critical Care, and Sleep Medicine, Department of Medicine, Icahn School of Medicine at Mount Sinai, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- 6Divisions of Rheumatology, John T. Milliken Department of Medicine, Washington University School of Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- 7Departments of Anesthesia, University of California, Los Angeles David Geffen School of Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- 8Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY, USA
- 9Department of Stem Cell Biology and Regenerative Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, USA
Abstract
Complement protein C3 is crucial for immune responses in mucosal sites such as the lung, where it aids in microbe elimination and enhances inflammation. While trained immunity – enhanced secondary responses of innate immune cells after prior exposure – is well-studied, the role of the complement system in trained immune responses remains unclear. We investigated the role of C3 in trained immunity and found that alveolar macrophage C3 and C3aR1 expression increased in humans after an intranasal exposure to a training stimulus. In vivo , trained wild-type mice showed significantly elevated pro-inflammatory cytokines and increased C3a levels upon a second stimulus. Ex vivo , trained C3-deficient alveolar macrophages (AMs) displayed reduced chemokine and cytokine output as well as impaired phagocytosis and reactive oxygen species (ROS) production compared to wildtype AMs. Real-time confocal microscopy of live, intact mouse alveoli revealed that AMs internalize C3 rapidly after alveolar microinstillation, as compared to C3a. Correspondingly, the blunted cytokine output was restored by exogenous C3 but not by C3a. Inhibiting C3aR, both pharmacologically and with a genetic C3aR knockout, prevented this restoration, indicating the necessity of C3aR engagement. Mechanistically, trained WT AMs demonstrated enhanced glycolytic activity compared to C3-deficient AMs – a defect corrected by exogenous C3 in a C3aR-dependent manner. These findings reveal that C3 modulates trained immunity in AMs through C3aR signaling and highlight a novel role for C3 in trained immunity.
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BibTeX
@article{earhart2026c3c3ar,
title = {{The C3–C3aR axis modulates trained immunity in alveolar macrophages}},
author = {Alexander Earhart and Alberto Lopez and Josue I. Hernandez and Aasritha Nallapu and Deebly Chavez and Sayahi Suthakaran and Brian Yang and Jungheun Hyun and Rafael Aponte Alburquerque and Marick Starick and Lorena Garnica and Ayşe Naz Ozantürk and Rahul Kumar Maurya and Xiaobo Wu and Jeffrey A. Haspel and Jae Woo Lee and Jaime L. Hook and Hrishikesh S. Kulkarni},
journal = {eLife},
year = {2026},
month = aug,
doi = {10.7554/elife.104977.3},
url = {https://doi.org/10.7554/elife.104977.3},
note = {CC BY},
}
RIS
TY - JOUR
TI - The C3–C3aR axis modulates trained immunity in alveolar macrophages
AU - Alexander Earhart
AU - Alberto Lopez
AU - Josue I. Hernandez
AU - Aasritha Nallapu
AU - Deebly Chavez
AU - Sayahi Suthakaran
AU - Brian Yang
AU - Jungheun Hyun
AU - Rafael Aponte Alburquerque
AU - Marick Starick
AU - Lorena Garnica
AU - Ayşe Naz Ozantürk
AU - Rahul Kumar Maurya
AU - Xiaobo Wu
AU - Jeffrey A. Haspel
AU - Jae Woo Lee
AU - Jaime L. Hook
AU - Hrishikesh S. Kulkarni
PY - 2026
DA - 2026/08/18
JO - eLife
DO - 10.7554/elife.104977.3
UR - https://doi.org/10.7554/elife.104977.3
AB - Complement protein C3 is crucial for immune responses in mucosal sites such as the lung, where it aids in microbe elimination and enhances inflammation. While trained immunity – enhanced secondary responses of innate immune cells after prior exposure – is well-studied, the role of the complement system in trained immune responses remains unclear. We investigated the role of C3 in trained immunity and found that alveolar macrophage C3 and C3aR1 expression increased in humans after an intranasal exposure to a training stimulus. In vivo , trained wild-type mice showed significantly elevated pro-inflammatory cytokines and increased C3a levels upon a second stimulus. Ex vivo , trained C3-deficient alveolar macrophages (AMs) displayed reduced chemokine and cytokine output as well as impaired phagocytosis and reactive oxygen species (ROS) production compared to wildtype AMs. Real-time confocal microscopy of live, intact mouse alveoli revealed that AMs internalize C3 rapidly after alveolar microinstillation, as compared to C3a. Correspondingly, the blunted cytokine output was restored by exogenous C3 but not by C3a. Inhibiting C3aR, both pharmacologically and with a genetic C3aR knockout, prevented this restoration, indicating the necessity of C3aR engagement. Mechanistically, trained WT AMs demonstrated enhanced glycolytic activity compared to C3-deficient AMs – a defect corrected by exogenous C3 in a C3aR-dependent manner. These findings reveal that C3 modulates trained immunity in AMs through C3aR signaling and highlight a novel role for C3 in trained immunity.
SN - 2050-084X
ER -