Defective Activation by Antigen, Superantigen, and Con A in T Cell Glycosylation Mutants.

Abstract

Many glycoproteins are critically involved in T-cell activation. The structure/function relationship of individual proteins has been extensively studied. However, it is not known whether glycans on these glycoproteins play any role at all in the activation process. We have identified a panel of T-cell hybridoma mutants that cannot synthesize the glycosylphosphatidylinositol(GPI) anchor due to a defect in dolichol-phosphate-mannose(Dol-P-Man) biosynthesis. These mutants also cannot make full-length N-glycan precursors. The truncated oligosaccharide can be further processed to become complex, but not typical high mannose glycans. Interestingly, all of the Dol-P-Man mutants are defective in activation by antigen, superantigen, and Con A, despite normal T-cell receptor expression. The observed activation defect could be due to abnormal glycosylation, or due to the absence of GPI-anchored proteins, or both. In order to distinguish between these possibilities, the yeast Dol-P-Man synthase gene was stably transfected into the mutants, which restored full expression of surface GPI-anchored proteins. However, N-linked glycosylation was either partially or completely corrected in different transfectants. Correction of activation defects correlates well with the status of N-linked glycosylation, but not with the expression of GPI anchored proteins. Thus, N-linked glycosylation plays an important role in T cell activation and may provide a novel target for the development of immunosuppressive drugs.