Size heterogeneity of human lymphotoxin is due to O-linked glycosylation.

: Lymphotoxin (LT), a cytokine with antiviral and antitumor activities, is produced by activated T- and B-lymphocytes. The molecular weight (MW) of this glycoprotein has been reported to be 24 and 25 kDa for the mature molecule and 18.6 kDa for the recombinant form. Here we report that various human T- and B-cell lines as well as freshly stimulated T and B cells release LT molecules of different sizes, ranging from 23 to 27 kDa by SDS polyacrylamide gele electrophoresis (PAGE) analysis. Although individual cell lines produce LT of characteristic size, no firm association between the different MW forms with either the B or the T cell lineage could be established. The size heterogeneity of LT is due to O-linked glycosylation since only the removal of both N- and O-linked sugar residues but not removal of N-linked sugar residues alone, reduces the size of all forms to around 18.6 kDa, which corresponds to the calculated MW of the recombinant form of human LT.