| Abstract: | The main aim of our study was to investigate whether the marked decrease in the expression of peanut agglutinin (PNA) receptors during T-cell maturation in the mouse is accompanied by increased activity of sialyltransferase. By differential agglutination with PNA, mature thymocytes (PNA-) were separated from immature ones (PNA+) and the separated fractions were tested for their sialyltransferase activity with asialofetuin as acceptor. In parallel, sialyltransferase activities of hydrocortisone-resistant thymocytes and untreated thymocytes were also compared. Optimization of the enzyme assay revealed that previous results in the literature were obtained under suboptimal conditions. Using manganese chloride instead of magnesium chloride, we have now found that hydrocortisone-resistant thymocytes contain 3.3-fold more sialyltransferase activity compared to untreated thymocytes. PNA- thymocytes contain 8.1-fold more enzyme activity compared to the PNA+ cells. Studies with fluorescein conjugated PNA of the agglutinated and unagglutinated thymocyte fractions suggest that the trace amount of sialyltransferase activity found in the PNA+ fraction may result from 5 to 10% cross-contamination with PNA- cells. These results suggest that the cellular levels of sialyltransferase specific for asialofetuin may play an important role in T-cell differentiation. |
