Scientists have discovered more about the intricacies of Natural Killer cells, a unique type of white blood cell important in early immune responses to tumors and viruses.  

Unlike most cells of the immune system that are activated by molecules found on the pathogen or tumor, Natural Killer cells are shut down by a group of proteins found on healthy cells. These de-activating proteins, known as Human Leukocyte Antigens or HLA molecules are absent in many tumors and cells infected with viruses, leaving them open to attack by the Natural Killer cells. 

Natural Killer cells recognize the HLA molecules using an inbuilt surveillance system called "Killer cell immunoglobulin-like receptors" (KIR).

Using the Australian Synchrotron, the team determined the three dimensional shape of one of these key KIR proteins, termed KIR3DL1, which binds to a particular HLA molecule. This pairing is known to play a role in limiting viral replication in people with HIV, slowing the progression of the disease to AIDS. Better understanding the structure of KIR proteins may help to develop approaches to better utilize Natural Killer cells to combat viral infection.

"It is only possible to detect proteins, such as KIRs, using extremely high-end equipment. The use of the platform technologies at Monash and the Australian Synchrotron was absolutely essential to this project's success," said Professor Jamie Rossjohn of Monash University.

"Since KIR3DL1 is only a single member of a much larger family of receptors, the study provides key insight into how Natural Killer cells utilise other members of this important family of receptors to recognise virus-infected cells and tumours," said Associate Professor Andrew Brooks from the University of Melbourne. 

The findings were published today in Nature.