How does the immune system work? Self and non-self

The immune system’s core function is to distinguish between “self” (your own tissues) and “nonself” (anything foreign). In kidney transplantation, the main challenge is that the recipient’s immune system may recognize the transplanted kidney as nonself, triggering an immune attack that can damage the graft.

Human Leukocyte Antigens (HLA)

HLA are proteins found on the surface of almost every cell in the body, especially on white blood cells. Their primary role is selfrecognition. The immune system constantly “scans” these molecular barcodes to determine whether a cell belongs to the body or is an invader such as a virus, bacteria, or a transplanted organ.

• If the barcode matches: the immune system accepts the cell.

• If the barcode is foreign: the immune system attacks.

These proteins are encoded by genes within the Major Histocompatibility Complex (MHC) on Chromosome 6. Because there are thousands of genetic variations, it is extremely rare for two unrelated individuals to have a perfect HLA match—except identical twins.

Immune System Activation

When the immune system recognizes an allogeneic (nonself) organ, it activates T lymphocytes. These cells can:

• directly damage graft cells through cytotoxic activity

• activate other immune cells such as macrophages and B lymphocytes

This coordinated immune response is what leads to rejection if not properly controlled with immunosuppressive therapy.