Those few, triggering protein fragments are termed "immunodominant."
Unfortunately, the immune system sometimes makes poor choices about which epitopes to pay attention to, and which to ignore.
Understanding of how immunodominance is conferred would enable vaccine designers to shift the immune system spotlight to parts of pathogens that they cannot change in efforts to escape detection.
For example, a vaccine could be designed to target a protein fragment central to a virus's ability to reproduce, or to invade its prey.
As part of the immune response, T cells, one type of white blood cell, partner with dendritic cells to make careful decisions about which pieces of pathogens will trigger a full-scale immune attack.
Upon encountering an invader, a dendritic cell will "swallow it," cut it up, and carry the pieces to the nearest lymph node.
Once in the lymph node, major histocompatibility complex (Mhc) proteins inside the dendritic cell present immunodominant epitopes on the cell's surface for consideration by T cells gathered there.
Once activated by high enough levels of target epitope for long enough periods of time, T cells become armed and capable of destroying the pathogen in question.
Kinetic stability determines whether, in the face of competing reactions within the immune system, an epitope:Mhc complex can remain intact on the dendritic cell surface long enough to demand T cell attention.
Sant's team found that immunodominant peptides were likely to stay bound to Mhc molecules for an average of 150 hours, where nondominant epitopes held on for less than 10 hours.
"What's exciting is that kinetic stability is determined by how tightly an epitope fits into the Mhc protein, and we can control that fit with standard techniques," Sant said.
If confirmed, this discovery will bring immundominance and a major portion of the immune system under our control for the first time."