Organ rejection

Scientists have identified a hidden link between our immune system and the activation of cells,

that lead to organ rejection.

Discovery opens the way to develop new forms of treatment, that could prevent immune responses,

from attacking life saving tissue transplants.

The type of receptor on bone marrow cells, called signal regulatory protein alpha, or SIRP alpha,

has been identified as the body's watch dog responsible for dispatching the lymphocytes, 

that target and destroy foreign cells.

When we take cell from another persons body and put them into our own,

white blood cells sees them as foreign, and attempts to break them apart.

This is accompanied by swelling and fever.

Molecules on the cell wall, called MHC or major histocompatibility complex, 

identify the cells as self or foreign.

The T lymphocyte has receptors on its surface capable of recognising unknown MHC proteins,

and responds by attempting to breakup the foreign cell.

Lymphocyte are not born knowing whats foreign and what is not.

The need to be taught.

This is the job of another part of the immune system called the dendritic cell.

Dendritic cell chew up foreign proteins and leave them into their own MHC,

before displaying them on their surface.

The activated dendritic cells,  migrate to the body's lymph nodes where they interact with the T lymphocytes.

Exactly how dendritic cells identify foreign materials, is still a mystery.

Scientists experimented with mice which lacked T lymphocytes.

They found that the differences between the donor's and recipients SIRP alpha gene correlated,

with the recipients immune responses.

SIRP alpha is already known to be the protein which binds to another protein called CD47,

that triggers a range of immune responses in different white blood cells.

Monocytes are the white blood cells, that grow into dendritic cells.

Scientists believed that CD47 on monocytes interact with CIRP alpha receptors on foreign tissues,

setting off the entire id check processes.

Once the cells are activated they turn around and activate the rest of the immune system, 

that leads to the full blown rejection of the transplanted organ.

Scientist believe that a better match between the donors and recipients SIRP alpha genes, 

could help reduce the risk of the immune response being sparked off.

Even when organs are chosen to have closely matching MHC proteins, 

subtle  differences  can still produce immune responses.

1 in 10 hearts, and 1 in 20 transplanted kidneys will show signs of being rejected by the body,

with in the first year, in spite of being compatible.

To avoid rejections organ recipients need to be on treatments that suppress the immune system.

This makes them prone to infection and cancer, and raises the risk of heart attacks and strokes,

by increasing blood pressure.

New treatments based on SIRP alpha, might help to prolong the organ's life.