Effect of tunicamycin on the assembly and antigenicity of HLA antigens: analysis with monoclonal antibodies.

The effect of glycosylation on the assembly and antigenicity of HLA antigens was investigated by examining HLA antigens synthesized in the presence of the antibiotic tunicamycin, an inhibitor of asparagine-linked oligosaccharide addition, with monoclonal antibodies specific for a variety of antigenic determinants. The monoclonal antibody Q5/13 reactive with a determinant expressed on the beta chain of human Ia-like antigens immunoprecipitated alpha and beta subunits with reduced apparent molecular weights from tunicamycin-treated cells, indicating that glycosylation is not required for association of the Ia-like antigen alpha and beta subunits. Immunoprecipitation of HLA-A,B,C antigens from tunicamycin-treated cells with four monoclonal antibodies specific for the heavy chain and one specific for beta 2-microglobulin showed that the heavy-chain determinant detected by the antibody Q6/64 is absent from the non-glycosylated molecule. This is the first demonstration that carbohydrate addition during biosynthesis affects the protein conformation of the HLA-A,B,C heavy chain.