Evidence for chemical differences in HLA-DR molecules on autologous acute lymphoblastic leukemia and B-lymphoblastoid cell lines.

HLA-DR molecules on autologous acute lymphoblastic leukemia (ALL) and B-lymphoblastoid cell lines from two individuals were compared by immune precipitation and gel electrophoresis. Cells were surface labeled with 125I and proteins immunoprecipitated with specific monoclonal antibodies (MoAb). Two electrophoretically distinct bands were found in the HLA-DR beta chain region on both ALL cell lines in contrast to only one on each of the autologous B-lymphoblastoid cell lines. Differences in the electrophoretic mobility of the alpha chains were also observed with ALL and B-lymphoblastoid cell lines from one individual. Preclearing of radiolabeled cell lysates with MoAb specific for HLA-DQ and -DP molecules demonstrated that the complexity of the HLA-DR pattern is not the result of antibody cross-reactivity with alpha and beta chains from other class II products. Immunoprecipitation experiments indicated that two beta chain bands are observed with each of the parental HLA-DR molecules on the ALL but not the B-lymphoblastoid cell line from an HLA-DR3,7-positive individual. We conclude that the HLA-DR molecules expressed on ALL and B-lymphoblastoid cell lines from the same individual can differ chemically. Neuraminidase treatment reduced these electrophoretic differences, indicating that these molecules differ in their sialic acid content. Since small changes in class II molecules can profoundly alter cellular interactions, the functional significance of these differences requires further investigation.