Refolding of HLA-B27 heavy chains in the absence of β2m yields stable high molecular weight (HMW) protein forms displaying native-like as well as non-native-like conformational features: Implications for autoimmune disease

Refolding of the heavy chain of the Class I HLA molecule, HLA-B27, in the absence of β₂m, yields soluble high molecular weight (HMW) oligomers reminiscent of the oligomeric forms of β₂m-free heavy chains (FHCs) of class I HLA antigens observed on cell surfaces. Here we examine the structural characteristics of HMW B27 in respect of features potentially relevant to autoimmunity, such as: (a) retention of native-like structure, since this could facilitate non-canonical interactions with T-cell receptors even in the absence of bound β₂m and peptide, or (b) presence of non-native structure, since this could yield novel (non-self) antigenic conformational epitopes that could elicit immune attack. We report that HMW B27 is characterized by high secondary structural content, structural stability, stability to proteolysis by trypsin, and structural features that are both partly native-like, and partly non-native-like, as assessed through the binding of conformationally-distinguishing and cross-reacting scFv antibodies specifically selected against HMW B27. We also present cell ELISA data with conformation-specific scFv antibodies that distinguish between lymphocytes from individuals who are healthy and B27 positive, and those who are B27 positive but suffering from ankylosing spondylitis.