The role of N-linked oligosaccharides of MHC class II antigens in T cell stimulation

Abstract

A specific increase in T cell extracellular acidification rate has been demonstrated recently when complexes of purified MHC class II molecules and antigenic peptides interact with T cell receptors (TCRs) on cloned T cells. The present study shows that such measurements of an increase in extracellular acidification rate can be used to evaluate the functional role of various N-linked oligosaccharides of MHC class II antigens. Affinity-purified murine IA k and IA s were deglycosylated in the presence of aspargine-amidase enzyme and were characterized by SDS-polyacrylamide gel electrophoresis. The complete removal of all three N-linked oligosaccharides from the α/β heterodimer was confirmed by four different lectin-linked Western blot analyses. Similar to the native heterodimer, both deglycosylated IA k and deglycosylated IA s were fully capable of binding synthetic antigenic peptides derived from myelin basic protein (MBP). When equivalent amount of glycosylated and deglycosylated class II-peptide complexes were exposed to restricted cloned T cells, identical increases in T cell extracellular acidification rates were observed. The specificity of such increases in extracellular acidification rate was demonstrated by exposing cloned T cells to irreleBant complexes of glycosylated and deglycosylated class II and antigenic peptides. These results show how measurement of extracellular acidification rate can be used to study structure-function correlations of ligand-receptor interactions, and support an earlier observation that N-linked oligosaccharides of murine MHC class II molecules are not involved in either antigenic peptide binding or T cell recognition.