1. Sense lipid antigens
Recognize self or microbial lipids displayed by CD1d—not free-floating lipid alone.
Natural Killer T (NKT) Cells
Lipid Sensors. Rapid Immune Coordinators.
NKT cells are specialized T lymphocytes that recognize lipid antigens presented by CD1d. They respond rapidly and help connect innate and adaptive immunity.
Back to all immune cells →What Are NKT Cells?
NKT cells have an αβ T-cell receptor and innate-like response properties. Unlike conventional T cells that usually recognize peptides on classical MHC, CD1d-restricted NKT cells recognize lipid antigens.
Type I, or invariant NKT (iNKT), cells have a semi-invariant TCR. Type II NKT cells use more diverse receptors. Activation can integrate antigen recognition and inflammatory cytokines.
NKT is not NK
NK cells
- Innate lymphoid lineage
- Lack a rearranged T-cell receptor
- Use activating and inhibitory receptors to assess targets
NKT cells
- Belong to the T-cell lineage
- Have an αβ T-cell receptor
- Recognize lipid antigens presented by CD1d
CD3⁺CD56⁺ “NKT-like” cells are not automatically CD1d-restricted NKT cells.
Key Functions of NKT Cells
Distinct NKT subsets help coordinate rapid responses; their effects depend on the tissue and inflammatory setting.
2. Release cytokines
Signals such as IFN-γ or IL-4 help shape the activity of other immune cells.
3. Coordinate immunity
Interact with dendritic cells, NK cells, B cells and other T cells.
4. Cytotoxic defense
Some NKT cells can kill target cells through perforin and granzymes.
How NKT Cells Work
Antigen recognition and inflammatory signals can contribute to activation.
1. Present lipids
An antigen-presenting cell loads a lipid antigen onto CD1d.
2. Recognize
The NKT TCR contacts the CD1d–lipid complex.
3. Activate
Activated cells rapidly produce cytokines and other effector signals.
4. Coordinate
Signals influence other immune cells and the local response.
Where Are They Found?
NKT cells occur in blood and tissues, including the liver. Their frequencies and distribution differ markedly between people and species; mouse findings do not translate directly to humans.
NKT Cells in Health and Disease
- Infection: contribute to early immune coordination.
- Cancer: antitumor responses and therapeutic approaches are being investigated.
- Inflammation and autoimmunity: effects can be protective or harmful, depending on the subset and context.
Much mechanistic evidence comes from animal studies.
NKT Cells and Aging
- A human study found lower blood iNKT-cell frequency and reduced proliferative responses in healthy older adults.
- Age-related patterns differ between invariant NKT cells and broader populations labeled NKT-like.
- These findings do not establish a validated NKT-based immune-age test.
Selected sources and references
- Bendelac et al., 2007 — The biology of NKT cells
- Peralbo et al., 2006 — iNKT cells in healthy elderly adults
Artwork illustrates the main mechanisms schematically; molecular sizes, colors and distances are not literal.