# Role of Spleen educated monocytes in mediating ischemia-reperfusion injury following lung transplant

> **NIH NIH R01** · NORTHWESTERN UNIVERSITY · 2021 · $591,457

## Abstract

PROJECT SUMMARY Primary graft dysfunction (PGD) after lung transplantation, resulting from ischemia
reperfusion injury (IRI), is the predominant cause of poor lung transplant outcomes. Pathologically, PGD is
characterized by neutrophil extravasation into the alveolar space. In murine models of lung transplantation,
NETosis of extravasated neutrophils induces irreversible allograft injury. Non-selective depletion of neutrophils
can ameliorate PGD, but is not clinically feasible given their importance in pathogen clearance. Accordingly,
we have focused on understanding the specific mechanisms that drive neutrophil extravasation into the
allograft leading to PGD after lung transplantation. We discovered that after lung transplantation, Ly6ClowCCR2-
non-classical monocytes (NCM), retained in the donor lung, and Ly6ChighCCR2+ classical monocytes (CM),
recruited to the allograft, are both necessary for the extravasation of neutrophils into the interstitial space and
the resulting lung injury. Both NCM and CM produce IL-1β in response to IRI, with differing consequences. We
present preliminary data suggesting that IL-1β produced by NCM activates donor alveolar macrophages (AM),
inducing their secretion of monocyte chemoattractant protein 1 (MCP-1) which results in recruitment of CM.
Our data also demonstrates that CM recruited to the allograft further produce IL-1β in response to signaling
through toll-like receptors, which permeabilizes the endothelium by downregulating the tight junction protein,
Zona Occludens 2 (ZO-2), to promote neutrophil extravasation. Using a genetic lineage tracing system and
heterochronic spleen transplants we reported that CMs originating in the bone marrow receive signals from the
spleen necessary for their function in mediating neutrophil extravasation after transplantation revealing the
spleen as an active immune organ in this response. We present preliminary data to support our hypothesis that
after lung transplantation, IL-1β released by donor NCM induces the secretion of MCP-1 from donor alveolar
macrophages, which is necessary for the recruitment of recipient CM primed by splenic red pulp macrophages.
This results in sustained IL-β signaling in the allograft that promotes neutrophil extravasation and graft injury.
We will test this hypothesis in two aims. Aim 1. To determine whether donor NCM and alveolar
macrophage-dependent MCP-1 secretion recruits host splenic CM to mediate neutrophil extravasation
after lung transplantation. Aim 2. To determine whether splenic endothelial fractalkine retains CM
recruited by TGF-β released from red pulp macrophages to prime the NLRP3 inflammasome. We use
causal genetic strategies in mouse models identify disease mechanisms and tie these experiments to
applicable therapies that can be tested in humans. In addition, we have taken care to pair our results with
unbiased analyses of human lung tissue obtained from biopsies of the donor lung before and at several times
after reperfusion d...

## Key facts

- **NIH application ID:** 10132385
- **Project number:** 5R01HL147575-03
- **Recipient organization:** NORTHWESTERN UNIVERSITY
- **Principal Investigator:** Ankit Bharat
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $591,457
- **Award type:** 5
- **Project period:** 2019-04-01 → 2023-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10132385

## Citation

> US National Institutes of Health, RePORTER application 10132385, Role of Spleen educated monocytes in mediating ischemia-reperfusion injury following lung transplant (5R01HL147575-03). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10132385. Licensed CC0.

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