Establishment of A Mouse Sepsis-Induced Immunosuppression Model By Intranasal Instillation of Bacteria

Sepsis is a life-threatening organ failure caused by the host's inappropriate response to infection. Pneumonia is the primary cause of sepsis. Animal models are important tools for studying the pathogenesis of sepsis and evaluating new treatment strategies. Previous animal models of sepsis lacked natural infection pathways, making it difficult to accurately reflect the clinical infection process. This study introduced a mouse sepsis immunosuppression model established by intranasal instillation of Klebsiella pneumoniae (KP) to simulate the natural respiratory infection pathway. After modeling with different concentrations of KP, the inflammation of the model was evaluated at 12 h for cytokine interleukin-6 (IL-6) levels, and organ damage was evaluated at 24 h for alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatine kinase (CK), and blood urea nitrogen (BUN) levels. The survival rate of the model was analyzed after 7 days. The percentage of lymphocytes and white blood cells, the proportion of major histocompatibility complex class II (MHC-II) expression in monocytes, and the mean fluorescence intensity (MFI) of IL-10 and TGF-β1 in CD4⁺ T cells were observed to evaluate the immune suppression in mice. After 7 days of modeling, a secondary infection was performed by intranasal instillation of Pseudomonas aeruginosa (PA). The bacterial load in bronchoalveolar lavage fluid (BALF) 24 h after secondary infection and the mortality rate within 14 days were assessed to further evaluate the model's immune suppression. Nasal instillation of high-concentration Klebsiella pneumoniae can effectively induce an immune suppression. Its purpose is to simulate sepsis induced by a natural respiratory infection pathway and to provide a standard model for sepsis research in animals.