Neutrophils are essential for innate immunity as the first line of defence. Neutrophils act as phagocytic white blood cells to kill bacteria and other microorganisms. A strong respiratory burst of neutrophils, dependent on reactive oxygen species, is produced during phagocytosis. Platelet-activating factor (PAF) is a signalling molecule with several prominent roles in tissue injury, inflammation, and platelet aggregation. However, the detailed mechanisms and intracellular signalling pathways involved in PAF-mediated neutrophil activation remain unclear. Here, we investigated the effect of PAF on changes in calcium concentration ([Ca²⁺]_i) and oxygen radical (O₂⁻) generation in activating canine neutrophils. We further evaluated these effects of PAF with inhibition of G protein-coupled receptors using the specific inhibitor suramin. Blood samples were collected from a total of five dogs and neutrophils were isolated. PAF stimulation of canine neutrophils caused an increase in [Ca²⁺]_i as well as the generation of O₂⁻, and the PAF receptor was sensitive to suramin. The results suggested that PAF stimulation of canine neutrophils may cause Ca²⁺ influx from the endoplasmic reticulum into the cytoplasm (as the first wave) and then trigger store-operated Ca²⁺ entry (as the second wave), which is an important intracellular signal transduction pathway for neutrophil activation. Furthermore, O₂⁻ generation by PAF stimulation may depend on the intracellular signalling pathway, with increasing inositol trisphosphate levels and [Ca²⁺]_i via G protein-coupled receptors. The finding that PAF-activating platelet aggregation is involved in canine neutrophil activation suggests a close relationship between haemostasis and neutrophil activation in dogs, offering new insight into the response to infection.

作为第一道防线，中性粒细胞对于先天免疫至关重要。中性粒细胞充当吞噬白细胞以杀死细菌和其他微生物。中性粒细胞的强烈呼吸爆发，依赖于活性氧，在吞噬过程中产生。血小板激活因子 (PAF) 是一种信号分子，在组织损伤、炎症和血小板聚集中具有多种重要作用。然而，参与 PAF 介导的中性粒细胞活化的详细机制和细胞内信号通路仍不清楚。在这里，我们研究了 PAF 对钙浓度 ([Ca ²⁺ ] _i ) 和氧自由基 (O ₂ ^-) 产生激活犬中性粒细胞。我们进一步评估了使用特异性抑制剂苏拉明抑制 G 蛋白偶联受体的 PAF 的这些作用。从总共五只狗中采集血样并分离出嗜中性粒细胞。犬中性粒细胞的PAF刺激引起[Ca ²⁺ ] _i的增加以及O ₂ ^-的产生，并且PAF受体对苏拉明敏感。结果表明，PAF 刺激犬中性粒细胞可能导致 Ca ²⁺从内质网流入细胞质（作为第一波），然后触发储存操作的 Ca ²⁺进入（作为第二波），这是中性粒细胞激活的重要细胞内信号转导途径。此外，通过 PAF 刺激产生 O ₂ ^-可能取决于细胞内信号通路，通过 G 蛋白偶联受体增加肌醇三磷酸水平和 [Ca ²⁺ ] _{i 。}PAF激活血小板聚集参与犬中性粒细胞激活的发现表明止血和中性粒细胞激活之间存在密切关系，这为对感染的反应提供了新的见解。