Well-trained immune cells keep HIV in check
A computer model proposes a solution to a long-standing mystery in HIV research — why a small percentage of people infected with the virus never develop full-blown AIDS. The answer lies in how the immune cells that recognize invaders are educated, and suggests new strategies for designing an HIV vaccine.
The human immune system detects foreign cells with the help of cell-surface proteins called human leukocyte antigens (HLAs). Each person’s cells carry a particular set of HLA molecules — the person’s HLA type — which bind fragments of virus or bacterial protein and ‘present’ them to T cells, the immune cells that recognize and attack infected cells. But before T cells are ready to perform their killer function, they are in effect trained on fragments of the body’s own proteins — self-peptides — in an organ called the thymus. To ‘graduate’ from the thymus, a T cell must be able to recognize at least one combination of HLA molecule and self-peptide, which provides the template for its subsequent immune response against a foreign peptide bound to that HLA molecule. T cells that bind to self-peptides very strongly, however, are rejected, as they would attack the body’s own cells.