THE ROLE OF N-LINKED OLIGOSACCHARIDES OF MHC CLASS-II ANTIGENS IN T-CELL STIMULATION

A specific increase in T cell extracellular acidification rate has bee n demonstrated recently when complexes of purified MHC class II molecu les and antigenic peptides interact with T cell receptors (TCRs) on cl oned T cells. The present study shows that such measurements of an inc rease in extracellular acidification rate can be used to evaluate the functional role of various N-linked oligosaccharides of MHC class II a ntigens. Affinity-purified murine IA(k) and IAS were deglycosylated in the presence of aspargine-amidase enzyme and were characterized by SD S-polyacrylamide gel electrophoresis. The complete removal of all thre e N-linked oligosaccharides from the alpha/beta heterodimer was confir med by four different lectin-linked Western blot analyses. Similar to the native heterodimer, both deglycosylated IA(k) and deglycosylated I A(5) were fully capable of binding synthetic antigenic peptides derive d from myelin basic protein (MBP). When equivalent amount of glycosyla ted and deglycosylated class II-peptide complexes were exposed to rest ricted cloned T cells, identical increases in T cell extracellular aci dification rates were observed. The specificity of such increases in e xtracellular acidification rate was demonstrated by exposing cloned T cells to irrelevant complexes of glycosylated and deglycosylated class II and antigenic peptides. These results show how measurement of extr acellular acidification rate can be used to study structure-function c orrelations of ligand-receptor interactions, and support an earlier ob servation that N-linked oligosaccharides of murine MHC class II molecu les are not involved in either antigenic peptide binding or T cell rec ognition.