A new study has shown how the body continuously screens and inspects the identity of cells to determine whether they are 'self' or 'foreign.'
The study, led by Prof. Israel Pecht of the Weizmann Institute's Immunology Department, has revealed that how the body's 'reconnaissance unit' continuously screens and inspects identity.
White blood cells called T cells employ specialized receptors called TCRs (T-cell receptors) for cell identification.
TCRs bind to molecules present on all our body's cells that act as 'self-I.D. cards.' Small fragments of bodily components bound to grooves in these molecules provide additional confirmation that the cell is ours and intruder-free.
TCRs, when they examine these complexes (antigens), are able to spot foreign bits, even when one amino acid in the antigen is out of order, and can pick just one infected cell out of thousands of healthy ones, even when they harbour a previously unknown virus.
The researchers have in their study provided a first step-by-step understanding of the interaction process.
Using a method, which resolves the biological events at millisecond intervals, the team was able to show how TCR binding progresses through time.
The analysis found that binding of the TCR to the antigen takes place in two separate stages, confirming the widely held theory that the process is an 'induced fit': The original physical contact between the two molecules initiates the second step, in which conformational changes occur in the receptor as it moulds itself to fit the antigen shape.
Pecht said that the research might go a long way toward explaining a seeming paradox of long standing: How T cells can be highly specific, able to precisely identify a particular protein structure, and yet able to bind to a very wide variety of protein molecules.
The findings might lead to deeper insights into the immune system and its function, and could yield new directions in pharmaceutical and medical research.
The study is published in the Proceedings of the National Academy of Sciences (PNAS).