Department of Pathology, Johns Hopkins University, School of Medicine, Baltimore, MD, United States.
Front Immunol. 2023 Oct 16;14:1277609. doi: 10.3389/fimmu.2023.1277609. eCollection 2023.
HLA-DO (DO) is an accessory protein that binds DM for trafficking to MIIC and has peptide editing functions. DO is mainly expressed in thymic medulla and B cells. Using biochemical experiments, our lab has discovered that DO has differential effects on editing peptides of different sequences: DO increases binding of DM-resistant peptides and reduces the binding of DM-sensitive peptides to the HLA-DR1 molecules. In a separate line of work, we have established that appropriate densities of antigen presentation by B cells during the contraction phase of an infection, induces quiescence in antigen experienced CD4 T cells, as they differentiate into memory T cells. This quiescence phenotype helps memory CD4 T cell survival and promotes effective memory responses to secondary Ag challenge.
Based on our mechanistic understanding of DO function, it would be expected that if the immunodominant epitope of antigen is DM-resistant, presentation of decreased densities of pMHCII by B cells would lead to faulty development of memory CD4 T cells in the absence of DO. We explored the effects of DO on development of memory CD4 T cells and B cells utilizing two model antigens, H5N1-Flu Ag bearing DM-resistant, and OVA protein, which has a DM-sensitive immunodominant epitope and four mouse strains including two DO-deficient Tg mice. Using Tetramers and multiple antibodies against markers of memory CD4 T cells and B cells, we tracked memory development.
We found that immunized DR1DO-KO mice had fewer CD4 memory T cells and memory B cells as compared to the DR1DO-WT counterpart and had compromised recall responses. Conversely, OVA specific memory responses elicited in HA immunized DR1+DO-KO mice were normal.
These results demonstrate that in the absence of DO, the presentation of cognate foreign antigens in the DO-KO mice is altered and can impact the proper development of memory cells. These findings provide new insights on vaccination design leading to better immune memory responses.
HLA-DO（DO）是一种辅助蛋白，可与 DM 结合以运输至 MIIC，并具有肽编辑功能。DO 主要在胸腺髓质和 B 细胞中表达。通过生化实验，我们实验室发现 DO 对不同序列的编辑肽具有不同的作用：DO 增加了 DM 抗性肽的结合，降低了 DM 敏感肽与 HLA-DR1 分子的结合。在另一项工作中，我们已经确定，在感染的收缩阶段，B 细胞适当密度的抗原呈递会使经历抗原的 CD4 T 细胞静止，因为它们分化为记忆 T 细胞。这种静止表型有助于记忆 CD4 T 细胞的存活，并促进对二次 Ag 挑战的有效记忆反应。
基于我们对 DO 功能的机制理解，如果抗原的免疫优势表位是 DM 抗性的，那么 B 细胞呈递减少密度的 pMHCII 会导致在没有 DO 的情况下记忆 CD4 T 细胞的错误发育。我们利用两种模型抗原（携带 DM 抗性的 H5N1-Flu Ag 和具有 DM 敏感免疫优势表位的 OVA 蛋白）以及包括两种 DO 缺陷型 Tg 小鼠在内的四个小鼠品系，探索了 DO 对记忆 CD4 T 细胞和 B 细胞发育的影响。使用 Tetramers 和针对记忆 CD4 T 细胞和 B 细胞标志物的多种抗体，我们跟踪了记忆的发展。
我们发现，与 DR1DO-WT 对照相比，免疫 DR1DO-KO 小鼠的 CD4 记忆 T 细胞和记忆 B 细胞较少，并且回忆反应受损。相反，在 HA 免疫的 DR1+DO-KO 小鼠中引发的 OVA 特异性记忆反应是正常的。
这些结果表明，在缺乏 DO 的情况下，DR1DO-KO 小鼠中同种异体外来抗原的呈递发生改变，并可能影响记忆细胞的正常发育。这些发现为导致更好免疫记忆反应的疫苗设计提供了新的见解。
