Related Experiment Video
Updated: Jul 20, 2026
Two Flow Cytometric Approaches of NKG2D Ligand Surface Detection to Distinguish Stem Cells from Bulk Subpopulations in Acute Myeloid Leukemia
Published on: February 21, 2021
CD94/NKG2A inhibits NK cell activation by disrupting the actin network at the immunological synapse
Madhan Masilamani1, Connie Nguyen, Juraj Kabat
1Receptor Cell Biology Section, Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
Insights
The CD94/NKG2A receptor prevents NK cell activation by disrupting the actin network and excluding lipid rafts at the inhibitory synapse (iNKIS). This maintains immune balance by preventing co-localization of activating receptors.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Immune responses rely on a balance between activating and inhibitory signals.
- The precise mechanisms by which inhibitory signals override activation signals in immune cells are not fully understood.
- Human CD94/NKG2A is an inhibitory receptor on NK cells and CD8+ T cells that recognizes HLA-E.
Purpose of the Study:
- To elucidate the molecular mechanisms by which CD94/NKG2A engagement inhibits NK cell activation.
- To investigate the role of the actin cytoskeleton and lipid rafts in the formation of the inhibitory NK cell immunological synapse (iNKIS).
Main Methods:
- Investigated the effect of CD94/NKG2A engagement on actin network dynamics and lipid raft localization at the immune synapse.
- Utilized techniques to assess protein phosphorylation, including Vav1 and ezrin-radixin-moesin proteins.
- Examined the impact of inhibiting actin polymerization and depleting cholesterol on iNKIS formation.
Main Results:
- CD94/NKG2A engagement disrupts the actin network and excludes lipid rafts from the iNKIS.
- This process involves the recruitment and activation of SHP-1, leading to dephosphorylation of Vav1 and ERM proteins.
- Inhibition of actin polymerization, but not cholesterol depletion, abolished lipid raft exclusion at the iNKIS.
- CD94/NKG2A prevents the recruitment of activating receptor complexes to the inhibitory synapse.
Conclusions:
- Lipid raft exclusion at the iNKIS is an active, cytoskeleton-dependent process.
- CD94/NKG2A maintains an inhibitory state at the synapse by preventing the co-localization of activating receptors.
- This mechanism ensures a balanced immune response by spatially segregating inhibitory and activating signals within the same NK cell.
Abstract:
An adequate immune response is the result of the fine balance between activation and inhibitory signals. The exact means by which inhibitory signals obviate activation signals in immune cells are not totally elucidated. Human CD94/NKG2A is an ITIM-containing inhibitory receptor expressed by NK cells and some CD8+ T cells that recognize HLA-E. We show that the engagement of this receptor prevents NK cell activation by disruption of the actin network and exclusion of lipid rafts at the point of contact with its ligand (inhibitory NK cell immunological synapse, iNKIS). CD94/NKG2A engagement leads to recruitment and activation of src homology 2 domain-bearing tyrosine phosphatase 1. This likely explains the observed dephosphorylation of guanine nucleotide exchange factor and regulator of actin, Vav1, as well as ezrin-radixin-moesin proteins that connect actin filaments to membrane structures. In contrast, NK cell activation by NKG2D induced Vav1 and ezrin-radixin-moesin phosphorylation. Thus, CD94/NKG2A prevents actin-dependent recruitment of raft-associated activation receptors complexes to the activating synapse. This was further substantiated by showing that inhibition of actin polymerization abolished lipid rafts exclusion at the iNKIS, whereas cholesterol depletion had no effect on actin disruption at the iNKIS. These data indicate that the lipid rafts exclusion at the iNKIS is an active process which requires an intact cytoskeleton to maintain lipid rafts outside the inhibitory synapse. The net effect is to maintain an inhibitory state in the proximity of the iNKIS, while allowing the formation of activation synapse at distal points within the same NK cell.
Related Concept Videos
01:28Cells of the Innate Immune Response
Phagocytes
Phagocytes police the peripheral tissues by removing cellular debris and responding to the invasion of foreign substances or pathogens. Many phagocytes attack and remove microorganisms even before lymphocytes detect them. The human body has two general...
02:26NF-κB-dependent Signaling Pathway
NF-κB-dependent Signaling Mechanism
The heterodimer of NF-κB...
01:27Cytotoxic T Cells-mediated Immune Response
Immunological surveillance is the ability of immune cells to monitor and eliminate infected cells with intracellular pathogens, neoplastically transformed cells, and cells with non-self antigens. Cytotoxic T cells and NK...
01:22T Cell Activation and Clonal Selection
Naive T cells that have not yet encountered an antigen express two primary CD...
01:31Immunoglobulin-like Cell Adhesion Molecules
Ig-CAMs exhibit either homophilic binding (to other Ig-CAMs) or heterophilic binding (to other ligands such as integrins). While most Ig-CAMs...
01:25Immune Surveillance by NK Cells and Phagocytes
Natural Killer Cells: The Fast Responders
NK cells are large granular lymphocytes found in the blood and lymphatic system. These...