Major histocompatibility complex class I-dependent cell binding to isolated Ly-49A: evidence for high-avidity interaction.
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.
Chang
C S
CS
Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Canada.
Shen
L
L
Gong
D E
DE
Kane
K P
KP
D000818:Animals; D000950:Antigens, Ly; D002352:Carrier Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D002448:Cell Adhesion / Q000276:immunology; D006183:H-2 Antigens / Q000096:biosynthesis / Q000378:metabolism* / Q000502:physiology; D064532:Histocompatibility Antigen H-2D; D037181:Lectins, C-Type; D008223:Lymphoma; D008565:Membrane Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D011485:Protein Binding / Q000276:immunology; D055630:Receptors, NK Cell Lectin-Like; D014407:Tumor Cells, Cultured
D000950:Antigens, Ly; D002352:Carrier Proteins; D006183:H-2 Antigens; D064532:Histocompatibility Antigen H-2D; D037181:Lectins, C-Type; D008565:Membrane Proteins; D055630:Receptors, NK Cell Lectin-Like