Objective To investigate the antigen presentation characteristics of dendritic cells (DC) and B cells in cardiac grafts. Methods The heart of BALB/c mice was transplanted into the abdominal cavity of C57BL/6J mice. CD45⁺ cells in the heart graft were extracted and sorted by flow cytometry at postoperative 5 d, and single cell RNA sequencing was performed. Taking DC and B cell subsets in cardiac grafts as the main study cells, the changing trend, antigen presenting ability and intercellular communication with T cells after heart transplantation were analyzed by bioinformatics analysis and flow cytometry. Gene ontology (GO) function enrichment difference analysis was adopted to prove the specific function and the reliability annotation of cell subsets. Results Germinal center-like B cell (GC-L B) was the B cell subset with the largest increase in quantity during the acute rejection phase, accounting for 87%. Classical DC (cDC) 2 was the only DC subset with a significant increase in quantity during acute rejection of heart transplantation, accounting for 44% of DC subset, and it occupied the highest communication intensity with T cells after heart transplantation. Mononucleated DC (moDC) and memory B cell (MBC) were the main transmitters of T cell input signals in non-transplanted hearts, whereas transformed into cDC2 and GC-L B during the acute rejection phase. Among them, MBC and GC-L B were the main sources of T cell input signals in non-transplanted hearts and heart grafts. Conclusions Compared with DC, B cells occupy a higher number and weight in the intercellular communication with T cells in non-transplanted hearts and heart grafts, prompting that the antigen presenting activity of B cells is more active and stronger than DC in the early stage of acute rejection of heart transplantation.

Chronic obstructive pulmonary disease （COPD） is susceptible to systemic complications. Especially，sarcopenia is an independent risk factor for COPD patients that can exacerbate respiratory muscle fatigue，lead to a higher risk of falls and fractures，and lower the quality of life. The pathogenesis of sarcopenia involves such aspects as mitochondrial dysfunction，insulin resistance，changes in skeletal muscle fiber types，and an imbalance in protein synthesis and breakdown. As nutrition support and exercise rehabilitation therapy frequently have limited effectiveness，it is urgent to find a way to slow the progression of COPD with sarcopenia. Numerous studies conducted in recent years have discovered a potential link between pulmonary microbiome disorders and the gut microbiota of COPD patients. Furthermore，a wide range of functions of gut microbiota and its metabolites have been demonstrated，such as regulating inflammation and immunity，glucose and lipid metabolism，and mitochondrial function. According to the Zangxiang theory in Chinese medicine， there are intimate connections between the spleen， intestine，and muscle，and gut microbiota may be the most essential part of ameliorating "spleen governing muscle" and increasing muscle mass and strength. This study aims to expound on the effect mechanism of gut microbiota in slowing the progression of COPD with sarcopenia，thereby furnishing novel perspectives and recommendations for forthcoming investigations and therapeutic applications.