Structural Relatedness of Distinct Determinants Recognized by Monoclonal Antibody TP25.99 on β2-Microglobulin-Associated and β2-Microglobulin-Free HLA Class I Heavy Chains

The association of HLA class I heavy chains with β2-microglobulin (β2m) changes their antigenic profile. As a result, Abs react with either β2m-free or β2m-associated HLA class I heavy chains. An exception to this rule is the mAb TP25.99, which reacts with both β2m-associated and β2m-free HLA class I heavy chains. The reactivity with β2m-associated HLA class I heavy chains is mediated by a conformational determinant expressed on all HLA-A, -B, and -C Ags. This determinant has been mapped to amino acid residues 194–198 in the α3 domain. The reactivity with β2m-free HLA class I heavy chains is mediated by a linear determinant expressed on all HLA-B Ags except the HLA-B73 allospecificity and on