Natural Killer T-Cells: What is their role in the immune system?

Natural Killer T-Cells (NKT) have been found to serve a diverse role in innate immunity.  NKT cells were named so because of their coexpression of a T-cell receptor along with the surface markers of a Natural Killer cell which speaks to the hybrid nature of these cells and their unique ability (3). These cells have been associated pathologically with allergy, autoimmunity, and atherosclerosis, but also play a role in clearance of pathogens and tumor surveillance among other things (1).  The question still remains as to how large a role these cells play in health and disease?

NKT cells are able to recognize lipid antigen presented by CD1, which closely resembles MHC I and is not polymorphic, on antigen presenting cells which allows them to recognize bacterial cell wall and the ability to react to types of antigen that T-cells cannot.  When activated these cells produce large quantities of Th1 and Th2 cytokines which can make predicting a type of immune response difficult, but also points to their potency in regulating the immune system opening up the door for development of therapeutics(2). What could happen in a person deficient in NKT cells or CD1?  Studies have been done in CD1 knockout mice with conflicting results and how those studies translate to humans is unclear.  Could NKTs be targets for possible therapeutics, vaccines, or anti-cancer drugs or would the off target effects be too great?  Evolutionary conservation of these cells could also point to their importance in the immune system.(3)  

Representing a small subpopultation of T-cells in mice and even smaller in humans more research needs to be done to reveal the mechanisms of NKT cells in the immune system.   Just how important are these cells?   The control NKTs seem to have over the immune response is exciting for the possibility of treatments for diseases that have eluded cures.

References:

1: Borgetal A et al.  Cd1d- lipid-antigen recongnition by the semi-invariant NKT T-cell receptor. Nature.  July 2007.

2: Godfrey D, Kronenberg M. Going both ways: Immune regulation via CD1d- dependent NKT cells.  Journal of Clinical Investigation.  November 2004.

3: Tupin E, Kinjo Y, Kronenberg M.  The unique role of the natural killer T cell in the response to microorganisms.  Nature Review.  June 2007.