The truncated IFITM3 facilitates the humoral immune response in inactivated influenza vaccine-vaccinated mice via interaction with CD81

A single-nucleotide polymorphism (SNP) rs12252-C of interferon-induced transmembrane protein 3 (<i>IFITM3</i>), resulting in a truncated IFITM3 protein lacking 21 N-terminus amino acids, is associated with severe influenza infection in the Chinese population. However, the effect of <i>IFITM3</i> rs12252-C on influenza vaccination and the underlying mechanism is poorly understood. Here, we constructed a mouse model with a deletion of 21 amino acids at the N-terminus (NΔ21) of IFITM3 and then compared the antibody response between Quadrivalent influenza vaccine (QIV) immunized wild-type (WT) mice and NΔ21 mice. Significantly higher levels of haemagglutination inhibition (HI) titre, neutralizing antibodies (NAb), and immunoglobulin G (IgG) to H1N1, H3N2, B/Victory, and B/Yamagata viruses were observed in NΔ21 mice compared to WT mice. Correspondingly, the numbers of splenic germinal centre (GC) B cells, plasma cells, memory B cells, QIV-specific IgG⁺ antibody-secreting cells (ASC), and T follicular helper cells (T_FH) in NΔ21 mice were higher compared with WT mice. Moreover, the 21-amino-acid deletion caused IFITM3 translocation from the endocytosis compartment to the periphery of cells, which also prevented the degradation of a co-stimulatory molecule of B cell receptor (BCR) CD81 on the cell surface. More importantly, a more interaction was observed between NΔ21 protein and CD81 compared to the interaction between IFITM3 and CD81. Overall, our study revealed a potential mechanism of NΔ21 protein enhancing humoral immune response by relocation to prevent the degradation of CD81, providing insight into SNP affecting influenza vaccination.

干扰素诱导跨膜蛋白3（interferon-induced transmembrane protein 3, IFITM3）的单核苷酸多态性（single-nucleotide polymorphism, SNP）rs12252-C可导致IFITM3蛋白截断，缺失N端21个氨基酸，该多态性与中国人群的重症流感感染相关。然而，IFITM3 rs12252-C对流感疫苗接种的影响及其潜在机制尚不清楚。本研究构建了IFITM3 N端缺失21个氨基酸（NΔ21）的小鼠模型，比较了四价流感疫苗（Quadrivalent influenza vaccine, QIV）免疫后野生型（wild-type, WT）小鼠与NΔ21小鼠的抗体反应。结果显示，与WT小鼠相比，NΔ21小鼠针对H1N1、H3N2、B/Victory和B/Yamagata病毒的血凝抑制（haemagglutination inhibition, HI）滴度、中和抗体（neutralizing antibodies, NAb）及免疫球蛋白G（immunoglobulin G, IgG）水平显著更高。相应地，NΔ21小鼠脾脏生发中心（germinal centre, GC）B细胞、浆细胞、记忆B细胞、QIV特异性IgG+抗体分泌细胞（antibody-secreting cells, ASC）及滤泡辅助性T细胞（T follicular helper cells, Tfh）的数量均高于WT小鼠。此外，21个氨基酸的缺失导致IFITM3从内吞区室转移至细胞外周，这也阻止了B细胞受体（B cell receptor, BCR）共刺激分子CD81在细胞表面的降解。更重要的是，NΔ21蛋白与CD81的相互作用较IFITM3与CD81的相互作用更强。综上，本研究揭示了NΔ21蛋白通过重定位阻止CD81降解从而增强体液免疫反应的潜在机制，为SNP影响流感疫苗接种效果提供了新的见解。