Equine influenza is a contagious respiratory disease caused by H3N8 type A influenza virus. Vaccination against equine influenza is conducted regularly; however, infection still occurs globally because of the short immunity duration and suboptimal efficacy of current vaccines. Hence the objective of this study was to investigate whether an adjuvant combination can improve immune responses to equine influenza virus (EIV) vaccines. Seventy-two mice were immunized with an EIV vaccine only or with monophosphoryl lipid A (MPL), polyinosinic-polycytidylic acid (Poly I:C), or MPL + Poly I:C. Prime immunization was followed by boost immunization after 2 weeks. Mice were euthanized at 4, 8, and 32 weeks post-prime immunization, respectively. Sera were collected to determine humoral response. Bone marrow, spleen, and lung samples were harvested to determine memory cell responses, antigen-specific T-cell proliferation, and lung viral titers. MPL + Poly I:C resulted in the highest IgG, IgG1, and IgG2a antibodies and hemagglutination inhibition titers among the groups and sustained their levels until 32 weeks post-prime immunization. The combination enhanced memory B cell responses in the bone marrow and spleen. At 8 weeks post-prime immunization, the combination induced higher CD8+ central memory T cell frequencies in the lungs and CD8+ central memory T cells in the spleen. In addition, the combination group exhibited enhanced antigen-specific T cell proliferation, except for CD4+ T cells in the lungs. Our results demonstrated improved immune responses when using MPL + Poly I:C in EIV vaccines by inducing enhanced humoral responses, memory cell responses, and antigen-specific T cell proliferation.

中文翻译：

---

单磷酰脂A和聚I:C组合增强马流感病毒疫苗的免疫反应

马流感是由H3N8甲型流感病毒引起的传染性呼吸道疾病。定期接种马流感疫苗；然而，由于现有疫苗的免疫持续时间短且功效欠佳，感染仍然在全球范围内发生。因此，本研究的目的是调查佐剂组合是否可以改善对马流感病毒（EIV）疫苗的免疫反应。 72 只小鼠仅使用 EIV 疫苗或使用单磷酰脂质 A (MPL)、聚肌胞苷酸 (Poly I:C) 或 MPL + Poly I:C 进行免疫。初次免疫2周后进行加强免疫。分别在初次免疫后 4、8 和 32 周对小鼠实施安乐死。收集血清以确定体液反应。采集骨髓、脾脏和肺样本以确定记忆细胞反应、抗原特异性 T 细胞增殖和肺病毒滴度。 MPL + Poly I:C 产生各组中最高的 IgG、IgG1 和 IgG2a 抗体和血凝抑制滴度，并维持其水平直至初次免疫后 32 周。该组合增强了骨髓和脾脏中的记忆 B 细胞反应。初次免疫后 8 周，该组合诱导肺部中 CD8+ 中央记忆 T 细胞频率和脾中 CD8+ 中央记忆 T 细胞频率更高。此外，除了肺部的 CD4+ T 细胞外，联合治疗组还表现出增强的抗原特异性 T 细胞增殖。我们的结果表明，在 EIV 疫苗中使用 MPL + Poly I:C 时，可通过诱导增强的体液反应、记忆细胞反应和抗原特异性 T 细胞增殖来改善免疫反应。