Localization of soluble major histocompatibility class II-peptide complexes on T cell surface

Affinity purified major histocompatibility (MHC)-peptide complexes are hete rodimeric cell surface glycoproteins and are known to recognize antigen-spe cific CD4(+) T cell receptors (TCRs). In general, the affinity of MHC-pepti de complexes to TCRs are considered very low with a K-D of 5 x 10(-5) M. an d, therefore, stabilization of these complexes on T cell surface was not re ported earlier. This could be due to (1)incomplete occupancy of MHC molecul es with antigenic peptides, (2) variability of the binding constant of pept ides to MHC molecules, (3) presence of endogenously bound peptides in MHC p reparations, or (4) a combination of these. Using well-characterized HLA-DR 2 complex loaded with a high affinity immunodominant epitope analog from hu man myelin basic protein (MBP), which shows release of gamma-IFN by specifi c stimulation of transformed human T cell clone (SS8T). The present report demonstrates a method for the localization of bound MHC class II-peptide co mplexes on T cell surface by backscatter electron imaging using in-lens Fie ld Emission Scanning Electron Microscopy (FESEM). The localization is speci fic to the complex recognized by the TCR on MHC class II (DR2) and MBP pept ide restricted human T cells. (C) 2000 Wiley-Liss, Inc.