Objective: To observe the effects of recombinant fusion protein interleukin (IL)-18 on the expression of immune-inflammatory factors in the mice infected with Staphylococcus aureus (SA), and to investigate the mechanism of action of IL-18 in defense of SA infection in vivo.
Methods: A total of 40 specific pathogen-free female BLAB/c mice were randomly divided into four groups: control, SA infection, immunized, and intervention. A mouse model of SA infection was established by nasal inoculation with SA liquid. The immunized group and the intervention group were intranasally given IL-18 before SA modeling, and then the SA infection group and the intervention group received the nasal inoculation with SA liquid; the control group was treated with phosphate buffered saline instead. The levels of IL-4, interferon (IFN)-γ, tumor necrosis factor (TNF), granulocyte colony-stimulating factor (G-CSF), IgM in the serum and bronchoalveolar lavage fluid (BALF) of mice were measured by enzyme-linked immunosorbent assay. The expression of macrophage inflammatory protein (MIP)-1α mRNA and MIP-2β mRNA in the lung tissue of mice were determined by real-time fluorescent quantitative PCR.
Results: Compared with the control group, the SA infection group and the immunized group had significantly higher levels of IL-4, G-CSF, and IgM in the serum and BALF and expression of MIP-1α mRNA and MIP-2β mRNA in the lung tissue (P<0.05); the SA infection group had a significantly lower level of IFN-γ and a significantly higher level of TNF in the serum and BALF (P<0.05); the immunized group had a significantly higher level of IFN-γ in the serum and BALF (P<0.05). Compared with the SA infection group, the intervention group had significantly higher levels of IL-4, IFN-γ, G-CSF, and IgM in the serum and BALF and expression of MIP-1α mRNA in the lung tissue. In contrast, the intervention group showed a significantly lower level of TNF in the serum and BALF and expression of MIP-2β mRNA in the lung tissue (P<0.05). All the above indicators in the intervention group were significantly higher than those in the control group (P<0.05), except the serum level of IFN-γ.
Conclusions: In the mice infected with SA, the recombinant fusion protein IL-18 by mucosal immunity can affect inflammatory factors in the serum and BALF and the expression of MIP-1α mRNA and MIP-2β mRNA in the lung tissue to promote the anti-infective immune response and enhance the ability to clear pathogens.
目的: 观察重组融合蛋白IL-18对金黄色葡萄球菌（SA）感染后小鼠体内免疫相关炎症因子表达的影响，探讨IL-18在体内防御SA感染的可能机制。
方法: 将40只SPF级雌性BLAB/c小鼠随机分为对照组、SA感染组、免疫组和干预组。采用鼻腔接种SA液建立SA感染小鼠模型，免疫组和干预组均在建模前以IL-18滴鼻，但免疫组不予SA接种，对照组以PBS进行替代处理。采用ELISA法测定各组小鼠血液及支气管肺泡灌洗液（BALF）中IL-4、干扰素-γ（IFN-γ）、肿瘤坏死因子（TNF）、粒细胞集落刺激因子（G-CSF）、IgM的浓度。实时荧光定量PCR技术检测各组小鼠肺组织中巨噬细胞炎性蛋白（MIP）-1α和MIP-2β mRNA表达水平。
结果: 与对照组相比，SA感染组和免疫组小鼠血清及BALF中IL-4、G-CSF、IgM浓度，以及肺组织中MIP-1α、MIP-2β mRNA含量均升高（P < 0.05）；SA感染组小鼠血清及BALF中IFN-γ水平降低，TNF水平升高（P < 0.05）；免疫组小鼠血清及BALF中IFN-γ水平升高（P < 0.05）。与SA感染组相比，干预组小鼠血清及BALF中IL-4、IFN-γ、G-CSF、IgM浓度，以及肺组织中MIP-1α mRNA含量均升高，血清及BALF中TNF水平，以及肺组织中MIP-2β mRNA含量均降低（P < 0.05）。除血清IFN-γ水平外，其余上述指标在干预组小鼠中均高于对照组（P < 0.05）。
结论: 重组融合蛋白IL-18经黏膜免疫小鼠，可改变SA感染后小鼠血清及BALF中炎症因子，以及肺组织中MIP-1α、MIP-2β mRNA的表达水平，从而促进机体的抗感染免疫反应，增强了机体清除病原体的能力。