Major histocompatibility complex class I-dependent cell binding to isolated Ly-49A: evidence for high-avidity interaction

Eur J Immunol. 1996 Dec;26(12):3219-23. doi: 10.1002/eji.1830261256.


Ly-49A molecules negatively regulate a subset of mouse natural killer (NK) cells, preventing lysis of H-2Dd-expressing target cells. In the present report, we immunoaffinity-purified Ly-49A from the EL4 lymphoma using the A1 monoclonal antibody (mAb) and examined cell adhesion to immobilized Ly-49A. Adhesion was observed by cells expressing relatively high levels of H-2Dd, but not cells expressing very low or no cell surface Dd, while antibodies specific for Dd or Ly-49A inhibited the cell binding, indicating that Dd and Ly-49A mediate the observed adhesion. The density of immobilized Ly-49A was varied and confirmed by ELISA. Cell binding exhibited a threshold Ly-49A density requirement, and above this threshold, increases in Ly-49A density resulted in substantial increases in cell adhesion to a high maximum cell binding. The density of Ly-49A homodimers required to mediate cell adhesion was found to be quite low: 140-250 molecules/microm2. These results suggest that the avidity of Ly-49A for Dd is relatively high and indicate that small changes in Ly-49A density near the threshold result in large changes in stable Ly-49A receptor engagement. The relatively sharp threshold and marked density dependence presented here for Ly-49A receptor engagement may explain the observation that relatively small differences in Ly-49A expression level on NK cells result in significant differences in functional outcome, i.e. whether a target cell expressing a low level of Dd is spared from lysis or not.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antigens, Ly*
  • Carrier Proteins / chemistry
  • Carrier Proteins / isolation & purification
  • Carrier Proteins / metabolism*
  • Cell Adhesion / immunology
  • H-2 Antigens / biosynthesis
  • H-2 Antigens / metabolism*
  • H-2 Antigens / physiology
  • Histocompatibility Antigen H-2D
  • Lectins, C-Type
  • Lymphoma
  • Membrane Proteins / chemistry
  • Membrane Proteins / isolation & purification
  • Membrane Proteins / metabolism*
  • Mice
  • Mice, Inbred C57BL
  • Protein Binding / immunology
  • Receptors, NK Cell Lectin-Like
  • Tumor Cells, Cultured


  • Antigens, Ly
  • Carrier Proteins
  • H-2 Antigens
  • Histocompatibility Antigen H-2D
  • Lectins, C-Type
  • Membrane Proteins
  • Receptors, NK Cell Lectin-Like