MHC class II molecules function to present exogenous antigen-derived peptides to CD4 T cells to both drive T cell activation and to provide signals back into the class II antigen-presenting cell. Previous work established the presence of multiple GxxxG dimerization motifs within the transmembrane domains of MHC class II α and β chains across a wide range of species and revealed a role for differential GxxxG motif pairing in the formation of two discrete mouse class II conformers with distinct functional properties (i.e., M1-and M2-paired I-A^k class II). Biochemical and mutagenesis studies detailed herein extend this model to human class II by identifying an anti-HLA-DR mAb (Tü36) that selectively binds M1-paired HLA-DR molecules. Analysis of the HLA-DR allele reactivity of the Tü36 mAb helped define other HLA-DR residues involved in mAb binding. In silico modeling of both TM domain interactions and whole protein structure is consistent with the outcome of biochemical/mutagenesis studies and provides insight into the possible structural differences between the two HLA-DR conformers. Cholesterol depletion studies indicate a role for cholesterol-rich membrane domains in the formation/maintenance of Tü36 mAb reactive DR molecules. Finally, phylogenetic analysis of the amino acid sequences of Tü36-reactive HLA-DR β chains reveals a unique pattern of both Tü36 mAb reactivity and key amino acid polymorphisms. In total, these studies bring the paradigm M1/M2-paired MHC class II molecules to the human HLA-DR molecule and suggest that the functional differences between these conformers defined in mouse class II extend to the human immune system.

MHC II 类分子的功能是将外源抗原衍生肽呈递给 CD4 T 细胞，以驱动 T 细胞激活并向 II 类抗原呈递细胞提供信号。先前的工作在多种物种的 MHC II 类 α 和 β 链的跨膜结构域中确定了多个 GxxxG 二聚化基序的存在，并揭示了差异 GxxxG 基序配对在形成两个具有不同功能的离散小鼠 II 类构象异构体中的作用。属性（即，M1 和 M2 配对 IA ^k II 类）。本文详述的生化和诱变研究通过鉴定选择性结合 M1 配对 HLA-DR 分子的抗 HLA-DR mAb (Tü36)，将该模型扩展到人类 II 类。Tü36 mAb 的 HLA-DR 等位基因反应性分析有助于确定参与 mAb 结合的其他 HLA-DR 残基。TM 结构域相互作用和整个蛋白质结构的计算机模拟与生化/诱变研究的结果一致，并提供了对两种 HLA-DR 构象异构体之间可能的结构差异的深入了解。胆固醇消耗研究表明富含胆固醇的膜结构域在 Tü36 mAb 反应性 DR 分子的形成/维持中发挥作用。最后，对 Tü36 反应性 HLA-DR β 链的氨基酸序列进行系统发育分析，揭示了 Tü36 mAb 反应性和关键氨基酸多态性的独特模式。总的来说，这些研究将范例 M1/M2 配对的 MHC II 类分子引入人类 HLA-DR 分子，并表明小鼠 II 类中定义的这些构象异构体之间的功能差异延伸到了人类免疫系统。