Quantitation of antigen-presenting cell MHC class II/peptide complexes necessary for T-cell stimulation

Nature. 1990 Aug 9;346(6284):574-6. doi: 10.1038/346574a0.


The number of specific complexes formed between peptide and the class II major histocompatibility complex (MHC) molecules expressed by an antigen-presenting cell (APC) after exposure to protein antigens is unknown, as is the number that activates T cells. Presentation of foreign peptides by APC takes place when many class II molecules may be occupied by autologous peptides. We have now estimated the number of specific peptide/class II complexes per APC by quantitative immunoprecipitation of I-Ak after pulsing the APC with stimulatory levels of a radioactive immunogenic peptide derived from hen egg-white lysozyme protein. T cells were activated by APC that expressed as few as 210-340 specific peptide/class II complexes (0.1% of the I-Ak molecules). These figures were confirmed using anti-CD3 antibody bound to latex beads as an alternative activating ligand. This low number explains the simultaneous presentation of multiple foreign antigens, even in the face of peptide competition.

MeSH terms

  • Antigen-Presenting Cells / immunology*
  • Cell Line
  • Genes, MHC Class II
  • Histocompatibility Antigens Class II / immunology*
  • Humans
  • Lymphocyte Activation
  • Macromolecular Substances
  • Muramidase / immunology*
  • Peptide Fragments / immunology*
  • T-Lymphocytes / immunology*


  • Histocompatibility Antigens Class II
  • Macromolecular Substances
  • Peptide Fragments
  • Muramidase