Sialidase expression in activated human T lymphocytes influences production of IFN-

Abstract: Sialidases influence cellular activity by removing terminal sialic acid from glycoproteins and glycolipids. Four genetically distinct sialidases (Neu1–4) have been identified in mammalian cells. In this study, we demonstrate that only lysosomal Neu1 and plasma membrane-associated Neu3 are detected in freshly isolated and activated human T lymphocytes. Activation of lymphocytes by expo-sure to anti-CD3 and anti-CD28 IgG resulted in a ninefold increase in Neu1-specific activity after growth of cells in culture for 5 days. In contrast, the activity of Neu3 changed minimally in activated lymphocytes. The increase in Neu1 enzyme activity correlated with increased synthesis of Neu1-spe-cific mRNA. Neu1 was present on the surface of freshly isolated and activated CD4 and CD8 T lym-phocytes, as determined by staining intact cells with anti-Neu1 IgG and analysis by flow cytometry and by Western blot analysis of biotin-labeled cell surface proteins. Cell surface Neu1 was found tightly associated with a subunit of protective pro-tein/cathepsin A (PPCA). Compared with freshly isolated lymphocytes, activated cells expressed more surface binding sites for galactose-recogniz-ing lectins Erythrina cristagalli (ECA) and Arachis hypogaea. Growth of cells in the presence of sialidase inhibitors 2,3-dehydro-2-deoxy-N-acetylneuraminic acid or 4-guanidino-2-deoxy-2,3-dehydro-N-acetylneuraminic acid resulted in a smaller increase in number of ECA-binding sites and a greater amount of cell surface sialic acid in activated cells. Inhibition of sialidase activity also resulted in reduced expression of IFN- in acti-vated cells. The down-regulation of IFN- oc-curred at the transcriptional level. Thus, sialidase activity in activated T lymphocytes contributes to the hyposialylation of specific cell surface glyco-conjugates and to the production of IFN-. J. Leu-koc. Biol. 81: 284–296; 2007