Heterogeneity of HL-A antigen preparations is due to variable sialic acid content

Purified, papain-solubilized preparations of HL-A antigen from cultured human lymphoblastoid cells (HL-A2 and HL-A7,12 from RPMI 4265 cells and a mixture of HL-A3, W-25, HL-A12, and HL-A27 from IM-1 cells) show substantial charge heterogeneity in isoelectric focusing gels. This heterogeneity can be ascribed largely to variable numbers of sialic acid residues on each molecule. Neuraminidase (EC 3.2.1.18) treatment of the HL-A antigens as a function of time altered the band patterns in a manner demonstrating that up to three sialic acid residues are present on both first locus ("LA") and second locus ("Four") antigens. Neuraminidase treatment did not alter the specificity or specific activity of the purified antigens.