Objective Alveolar macrophages (AMs) are critical for maintaining the homeostasis of pulmonary microenvironment. They process surfactants to ensure alveoli patency, and also serve as the first line of immune defense against pathogen invasion. Available studies have shown that monocyte-derived AMs continuously release pro-inflammatory cytokines and chemokines, recruiting other immune cells to the damaged area during pulmonary fibrosis. These monocyte-derived AMs maintains and amplifies inflammation, playing a negative role in pulmonary fibrosis progression. Current researches have predominantly focused on the gene expression levels of AMs in pulmonary fibrosis microenvironment, with less emphasis on the function and regulation of proteins. This study aims to investigate the differentially expressed proteins (DEPs) of AMs under normal physiological conditions and after pulmonary fibrosis, in order to gain a more comprehensive understanding of the role of AMs in the progression of pulmonary fibrosis.Methods Firstly, the construction of bleomycin-induced pulmonary fibrosis mouse models was evaluated through using measurements such as body mass, lung coefficient, lung wet-to-dry weight ratio, H&E staining and Masson staining. Subsequently, AMs from both the saline controls and the pulmonary fibrosis models (2.5×10⁵ cells per sample) were collected using FACS sorting, and protein expression profiles of these cells were obtained through label-free proteomics approach. The quality of the proteomic data was assessed by comparing our saline control proteomic data with public proteomic data of physiological AMs. Thirdly, DEPs analysis between the saline controls and the bleomycin groups was carried out using R package Prostar. Functional enrichment analyses of significantly upregulated DEPs were performed using R package Clusterprofiler for GO and KEGG pathways. Finally, the STRING database was used to explore the protein-protein interaction networks related to phagocytosis regulation, inflammatory response regulation, and I-κB/NF-κB signaling pathway. The expression levels of Tlr2 and Pycard were detected respectively by FACS and western blotting.Results Compared to the saline controls, mice in the bleomycin groups exhibited a lower average body mass, extensive infiltration of inflammatory cells, and deposition of collagen in the lungs. This indicates that bleomycin successfully induced pulmonary fibrosis in mouse models. The proteomic data of AMs obtained from these models was of high quality and fulfilled the research requirements. A comprehensive analysis showed that 778 proteins were upregulated in pulmonary fibrosis groups compared with control groups. Moreover, the signal pathways enriched in up-regulated DEPs were related to the I-κB/NF-κB pathway, inflammatory response regulation, phagocytosis regulation, TGF-β signaling, and HIF-1 pathway, indicating that AMs in pulmonary fibrosis microenvironment exerted pro-inflammatory and pro-fibrotic functions. Protein-protein interaction network analysis of the DEPs suggested that the interactions between Tlr2 and Pycard were control nodes for the pro-inflammatory phenotype of AMs, thereby contributing to pulmonary fibrosis progression. Further validation by FACS and western blotting respectively confirmed that the expression levels of Tlr2 and Pycard in AMs were significantly increased after pulmonary fibrosis.Conclusion This study investigates the changes in the protein expression profile of AMs in the pulmonary fibrosis microenvironment. The results show that AMs notably enhanced the activity of various pathways associated with inflammation and fibrosis, suggesting that the interaction between Tlr2 and Pycard serves as a key control node for the highly pro-inflammatory behavior of AMs.