Conformation and surface expression of free HLA-CW1 heavy chains in the absence of beta(2)-microglobulin

A beta(2)-microglobulin (beta(2)m)-deficient kidney carcinoma cell line and three monoclonal antibodies to the alpha 1 (L31), alpha 2 (W6/32), and alpha 3 (Q1/28) domain of class I HLA molecules were selected to assess the role of beta(2)m in regulating the conformation and surface expression of HLA-C molecules. HLA-A2, -B27, and -CW1 molecules synthesized by beta(2)m-deficient cells were compared to heavy chains synthesized in transfectants expressing a large excess of beta(2)m. As assessed by differential binding with monoclonal antibodies and partitioning studies in the detergent TX-114, no HLA-A2, -B27, or -CW1 molecules can be expressed, in a correct conformation, by beta(2)m-deficient cells. These cells, however, do express low bur significant amounts of free HLA-CW1 heavy chains at the cell surface. Transfection with beta(2)m causes a coordinate change in the antibody reactivity of the three domains of HLA-CW1 molecules, thereby providing the first experimental demonstration that assembly with beta(2)m affects the folding of nor only the alpha 1 and alpha 2, but also of the alpha 3 domain. HLA-CW1 heavy chains, when free of beta(2)m, are less soluble in the detergent TX-114 than free HLA-B27 heavy chains, and when associated with beta(2)m share an alpha 3 domain epitope with free HLA-A2 and -B27 heavy chains. Moreover, their assembly with beta(2)m is largely incomplete. These data additionally demonstrate an impaired ability of HLA-CW1 ro properly fold and establish a dose similarity of HLA-CW1 to murine D-b and L-d molecules. Although the functional role, if any, of free HLA-CW1 heavy chains remains to be determined, the present study demonstrates that the absence of beta(2)m does not completely ablate class I expression in neoplastic cells of human origin. (C) American Society for Histocompatibility and Immunogenetics, 1997.