Inhibitory effects of tunicamycin on the mixed lymphocyte reaction and mitogen-induced lymphocyte blastogenesis

The role of asparagine(Asn)-linked saccharides on the surface of lymphocytes in cellular interactions was examined by performing studies on the effects of tunicamycin (TM), which inhibits the glycosylation of proteins N-glycosylated at asparagine residues, on the mixed lymphocyte reaction (MLR) and mitogen-induced lymphocyte blastogenesis of human lymphocytes by measuring 3H-thymidine (TdR) incorporation. Responses were expressed as percentages of that of the control (MLR without TM). The lymphocyte blastogenesis in the one- and two-way MLR were, respectively, 43.1% and 48.0% of the control at 0.1 microgram/ml of TM, and 5.5% and 7.2% at 1 microgram/ml of TM. The inhibitory effect of TM on the one-way MLR was shown using TM-pretreated stimulator cells, TM-pretreated responder cells or both. TM blocked lymphocyte blastogenesis in the secondary as well as in the primary MLR. The inhibitory effect of TM on the two-way MLR was observed when TM was added on day 0 to day 2, but not on day 4 of incubation. TM blocked mitogen-induced lymphocyte blastogenesis by phytohemagglutinin, concanavalin A or by pokeweed mitogen. As TM had no cytotoxic effect on cultured cells, these inhibitory effects of TM were thought to be due to the loss of Asn-linked saccharides from glycoprotein of the surface of lymphocytes. These findings indicated that Asn-linked saccharides of glycoprotein on the surface of lymphocytes were important in cellular interactions that are necessary for the cellular immune response.