What does this research mean for the field?

GM-CSF signaling deficiency causes pulmonary lymphocytosis through alveolar macrophage-mediated chemokine secretion, altered lymphoid lineage commitment, and local lymphocyte proliferation, which can be reversed by restoring GM-CSF signaling to alveolar macrophages. Novelty: ClaimNovelty.NOVEL_FINDING. Consensus alignment: ConsensusAlignment.NEUTRAL.

What question did this study set out to answer?

To investigate the mechanisms behind pulmonary lymphocytosis in GM-CSF signaling deficient mice.

May 20, 2026

B28-23 Gm-csf Signaling Deficiency Causes Marked Pulmonary Lymphocytosis Due to Alveolar Macrophage-mediated Recruitment, Altered Lymphoid-myeloid Lineage Commitment, and Local Proliferation

Key Points

To investigate the mechanisms behind pulmonary lymphocytosis in GM-CSF signaling deficient mice.
Used mice with GM-CSF gene knockout and wild type for comparative analysis.
Assessed lung histology, lymphocyte populations, chemokine levels, and gene expression.
Performed adoptive lymphocyte transfer and macrophage transplantation to evaluate cell functions.
GM-CSF deficient mice showed marked pulmonary lymphocytosis with increased B220+ and CD4+ populations compared to wild type (WT).
Increased chemokine and immunoglobulin levels were observed in the bronchoalveolar lavage fluid of GM-CSF deficient mice.
Macrophage replacement normalized lymphocyte trafficking and pulmonary lymphocytosis in GM-CSF deficient mice.

Abstract

Abstract Background Pulmonary lymphocytosis (PL)—lymphocyte accumulation in the lungs—is a pathologic manifestation of pulmonary alveolar proteinosis (PAP) and other lung diseases including chronic obstructive lung disease (COPD), pulmonary fibrosis, hypersensitivity pneumonitis, asthma and others; however, the mechanism(s) responsible are not known. Methods Mice with PAP caused by ablation of the gene encoding GM-CSF or it receptor α or β chains (Csf2KO, Csf2raKO, Csf2rbKO mice, respectively) and wild type (WT) mice were analyzed as follows (method-outcome): lung histology-PL, ELISA-chemokines and immunoglobulins in bronchoalveolar lavage fluid (BALF), single nuclear RNA sequencing with combinatorial indexing (snRNAseq)-lung gene expression, high-definition spatial-transcriptomics (HD-ST)-spatial lung gene cell expression, adoptive lymphocyte transfer-lymphocyte trafficking, quantitative real-time polymerase chain reaction (qRT-PCR)-alveolar macrophage (AM) and lung cell gene expression, immunohistochemistry (IHC)-cellular proliferation, pulmonary macrophage transplantation (PMT)-AM replacement. Results GM-CSF signaling deficient (GMSD) mice (Csf2KO, Csf2raKO, Csf2rbKO) exhibited marked PL (in peribronchovascular regions) while WT mice did not (lung histology) and had increased B220+ and CD4+ lymphocytes, CD138+ plasma cells, and CD68+ macrophages (IHC); lymphocytes were functional as shown by 100-fold higher immunoglobulin levels in GMSD compared to WT mice (ELISA-BALF). Importantly, AMs were present in all GMSD and WT mice as shown by histology, electron microscopy, and snRNAseq (Lgals3+, Spp1+). Compared to WT, GMSD AMs had increased mRNA encoding CD11b, Slfn4, ApoE and Gpnmb, reduced mRNA encoding Chil3, Car4, Mrc1, or Lpl, and increased mRNA encoding chemokines (Cxcl9, Cxcl10, Cxcl16) and proinflammatory cytokines (TNFα, TGFβ) (snRNAseq). Chemokines formed gradients across peribronchovascular regions (HD-ST) consistent with lymphocyte recruitment from blood. Adoptive transfer of green fluorescent protein-expressing splenocytes mice demonstrated increased pulmonary lymphocyte trafficking in GMSD compared to WT mice. Compared to WT, GMSD lung digest cells had increased mRNA encoding Bach2, Ebf1, FoxO1 and Pax5 and decreased levels of mRNA encoding Cebpα, Cebpβ, and Spi1, suggesting altered lymphoid lineage commitment. Compared to WT, GMSD mice lymphocytes were positive for Ki67 and Pax5 (IHC) indicating in situ proliferation. Replacement of AMs in GMSD mice reduced chemokine levels, PL, and immunoglobulins. Conclusion(s) In GMSD mice, AMs are present but have abnormal gene expression, phenotypes, and functions. PL in GMSD is caused by increased lymphocytes, altered lymphoid lineage commitment, and increased in situ lymphocyte replication and AMs are the main source of chemokine secretion. PL was normalized by PMT to restore GM-CSF signaling to AMs. Results expand our understanding of the role GM-CSF plays in connecting innate and adaptive immune responses in the lung. This abstract is funded by: R01HL085453 and R01HL118342 (BCT), and R01HL149743-A (PA)

Bookmark

Cite This Study

Arumugam et al. (Fri,) studied this question.

synapsesocial.com/papers/6a0d4fa9f03e14405aa9b048 https://doi.org/https://doi.org/10.1093/ajrccm/aamag162.1143

Bookmark