Respiratory Syncytial Virus (RSV) infection inhibits lung eosinophilia, but induces profound eosinophil degranulation in allergic mice

RSV诱导的婴儿细支气管炎的特征是鼻和气管吸出物中高浓度的嗜酸性粒细胞衍生蛋白，包括ECP、MBP和EDN。然而，试图证明呼吸道合胞病毒感染的婴儿的气道粘膜或分泌物中存在嗜酸性粒细胞的尝试一直不成功。用RSV或假接种感染OVA致敏、激发（通过反复OVA雾化）的小鼠，并在RSV或假接种后第1天通过支气管肺泡灌洗（BAL）回收的细胞中进行差异细胞计数。用特异性比色法测定BALF中的嗜酸性粒细胞过氧化物酶（EPO）活性，发现RSV感染的OVA攻击小鼠BALF中的嗜酸性粒细胞数量（1.3×10^5/ml）显著低于假感染的OVA攻击小鼠（4.0×10^5/ml）（p<0.001）。OVA攻击的假感染小鼠没有嗜酸性粒细胞脱粒的证据，因为在BAL液中不存在可检测的EPO活性。另一方面，OVA攻击的RSV感染小鼠在BAL液中具有高水平的EPO活性（p<0.01）。这些发现表明RSV感染与嗜酸性粒细胞的迁移和活化途径之间存在复杂的相互作用，这可能影响特应性和非特应性个体对呼吸道病毒感染的反应。

RSV-induced bronchiolitis in infants is characterized by high concentrations of eosinophil-derived proteins, including ECP, MBP, and EDN, in nasal and tracheal aspirates. However, attempts to demonstrate the presence of eosinophils in airway mucosa or secretions of infants with RSV infections have been unsuccessful.A BALB/c mouse model of lung eosinophilia (OVA-induced) was used. OVA-sensitized, challenged (by repeated OVA nebulization) mice were infected with RSV or sham-inoculated and differential cell counts were performed in cells recovered by bronchoalveolar lavage (BAL) at day 1 after RSV or sham inoculation. Eosinophil peroxidase (EPO) activity in the BAL fluid was measured by a specific colorimetric assay.A significant reduction in the number of BAL eosinophils was observed in RSV-infected OVA-challenged mice (1.3×10^5/ml) compared with sham-infected, OVA-challenged mice (4.0×10^5/m1) (p<0.001). OVA-challenged, sham infected mice had no evidence of eosinophil degranulation, as no detectable EPO activity was present in the BAL fluid. On the other hand, OVA-challenged, RSV-infected mice had high levels of EPO activity in BAL fluid (p<0.01).These findings suggest the existence of a complex interplay between RSV infection and the migratory and activation pathways of eosinophils that may affect the response of atopic as well as non-atopic individuals to respiratory viral infections.