Neonatal brain injury, especially severe injury induced by hypoxia-ischemia (HI), causes mortality and long-term neurological impairments. Our previous study demonstrated activation of CD11b⁺ myeloid cells, including residential microglial cells (MGs) and infiltrating monocyte-derived macrophages (MDMs) in a murine model of hypoxic-ischemic brain damage (HIBD), with unknown functions. Here, we study the differences in the phagocytic function of MGs and MDMs to clarify their potential roles after HIBD. HI was induced in 9–10-day postnatal mice. On days 1 and 3 after injury, pathological and neurobehavioral tests were performed to categorize the brain damage as mild or severe. Flow cytometry was applied to quantify the dynamic change in the numbers of MGs and MDMs according to the relative expression level of CD45 in CD11b⁺ cells. CX₃CR₁^GFPCCR₂^RFP double-transformed mice were used to identify MGs and MDMs in the brain parenchyma after HIBD. Lysosome-associated membrane protein 1 (LAMP1), toll-like receptor 2 (TLR2), CD36, and transforming growth factor (TGF-β) expression levels were measured to assess the underlying function of phagocytes and neuroprotective factors in these cells. The FITC-dextran 40 phagocytosis assay was applied to examine the change in phagocytic function under oxygen-glucose deprivation (OGD) in vitro. We found that neonatal HI induced a different degree of brain damage: mild or severe injury. Compared with mildly injured animals, mice with severe injury had lower weight, worse neurobehavioral scores, and abnormal brain morphology. In a severely injured brain, CD11b⁺ cells remarkably increased, including an increase in the MDM population and a decrease in the MG population. Furthermore, MDM infiltration into the brain parenchyma was evident in CX₃CR₁^GFPCCR₂^RFP double-transformed mice. Mild and severe brain injury caused different phagocytosis-related responses and neuroprotective functions of MDMs and MGs at 1 and 3 days following HI. The phagocytic function was activated in BV2 cells but downregulated in Raw264.7 cells under OGD in vitro. These observations indicate that neonatal HI induced different degrees of brain injury. The proportion of infiltrated macrophage MDMs was increased and they were recruited into the injured brain parenchyma in severe brain injury. The resident macrophage MGs proportion decreased and maintained activated phagocytic function in both mild and severe brain injury, and restored neuroprotective function in severe brain injury.

新生儿脑损伤，尤其是缺氧缺血（HI）引起的严重损伤，会导致死亡和长期神经功能障碍。我们之前的研究表明，在缺氧缺血性脑损伤（HIBD）小鼠模型中，CD11b ⁺骨髓细胞被激活，包括驻留小胶质细胞（MG）和浸润性单核细胞衍生巨噬细胞（MDM），其功能未知。在这里，我们研究 MG 和 MDM 吞噬功能的差异，以阐明它们在 HIBD 后的潜在作用。在出生后 9-10 天的小鼠中诱导 HI。受伤后第 1 天和第 3 天，进行病理学和神经行为测试，将脑损伤分为轻度或重度。应用流式细胞术根据CD11b ⁺细胞中CD45的相对表达水平来量化MG和MDM数量的动态变化。 CX ₃ CR ₁ ^GFP CCR ₂ ^RFP双转化小鼠用于鉴定 HIBD 后脑实质中的 MG 和 MDM。测量溶酶体相关膜蛋白 1 (LAMP1)、Toll 样受体 2 (TLR2)、CD36 和转化生长因子 (TGF-β) 表达水平，以评估这些细胞中吞噬细胞和神经保护因子的潜在功能。采用FITC-葡聚糖40吞噬实验检测氧糖剥夺（OGD）下吞噬细胞功能的变化体外。我们发现新生儿HI会引起不同程度的脑损伤：轻度或重度损伤。与轻度损伤的动物相比，重度损伤的小鼠体重较低，神经行为评分较差，大脑形态异常。 在严重损伤的大脑中，CD11b ⁺细胞显着增加，包括 MDM 群体的增加和 MG 群体的减少。此外，在 CX ₃ CR ₁ ^GFP CCR ₂ ^RFP双转化小鼠中，MDM 渗入脑实质是明显的。 HI后1天和3天，轻度和重度脑损伤引起MDM和MG不同的吞噬相关反应和神经保护功能。 OGD下BV2细胞的吞噬功能被激活，但Raw264.7细胞的吞噬功能下调体外。这些观察结果表明新生儿HI引起不同程度的脑损伤。在严重的脑损伤中，浸润的巨噬细胞MDM的比例增加，并被募集到受损的脑实质中。在轻度和重度脑损伤中，驻留巨噬细胞MG的比例降低并维持激活的吞噬功能，并在严重脑损伤中恢复神经保护功能。