BACKGROUND: Infantile pneumonia (IP) is a significant cause of morbidity and mortality in young children. Mesenchymal stem cells (MSCs) have emerged as potential therapeutic agents in pneumonia due to their immunomodulatory properties. The study analyzed the role of MSCs from bone marrow in IP and the underlying mechanism. METHODS: Human embryonic lung fibroblasts (WI-38) were stimulated using lipopolysaccharide (LPS) to mimic an IP cell model. This study employed flow cytometry to analyze the expression of hematopoietic markers and marker proteins on MSCs. The differentiation potential of MSCs was assessed through microscopy, oil red O staining, and alkaline phosphatase (ALP) assays. The localization of exosomes in WI-38 cells was observed using the cell membrane green fluorescent probe DIO. Quantitative reverse transcription polymerase chain reaction (qRT-PCR), western blotting and immunohistochemistry assays were used to analyze the expression of mRNA or protein. Cell viability, proliferation, and apoptosis were evaluated using Cell counting kit-8, 5-Ethynyl-2'-deoxyuridine, and flow cytometry assays, respectively. Enzyme-linked immunosorbent assays were conducted to measure cytokine levels. A mouse model of pneumonia was utilized to assess the therapeutic potential of MSC-derived exosomes on lung injury. Co-immunoprecipitation (Co-IP) assay was performed to study the interaction between Cbl proto-oncogene B (CBLB) and mitogen-activated protein kinase 14 (MAPK14). RESULTS: MSC-derived exosomes could be transferred into LPS-induced WI-38 cells, where they mitigated the inhibitory effects of LPS on CBLB mRNA expression. These exosomes improved WI-38 cell proliferation, reduced apoptosis, and decreased the production of pro-inflammatory cytokines including IL-6, IL-1β, and TNF-α by regulating CBLB after LPS treatment. Moreover, in a mouse model, MSC-derived exosomes protected against LPS-induced lung injury, whereas the effect was reversed after treatment with the exosomes isolated from CBLB-deficient MSCs. In addition, CBLB was found to destabilize MAPK14 protein expression in WI-38 cells. Further, overexpression of CBLB ameliorated LPS-induced inhibitory effect on cell proliferation and promoting effects on cell apoptosis and inflammation in WI-38 cells by regulating MAPK14. CONCLUSION: MSC-derived exosomal CBLB has therapeutic potential in ameliorating the progression of IP probably by ubiquitinating MAPK14, which could lead to novel clinical interventions for treating this condition.