Cell-surface recognition
The molecules displayed at a cell surface act as identifying markers. Differences in these markers allow the immune system to distinguish the body's own cells from foreign or abnormal material.
Many surface markers are proteins associated with the cell-surface membrane. Glycoproteins commonly perform this role, and glycolipids can also contribute to cell recognition.
Using these surface molecules, the immune system can identify:
- pathogens
- cells belonging to another organism of the same species
- abnormal body cells, including infected or cancerous cells
- toxins
Self and foreign cells
The combination of surface markers helps the immune system decide whether material belongs to the body or should be treated as foreign. The body's own cells carry markers recognised as self, while unfamiliar markers can identify non-self material.
This distinction also matters when tissue comes from another individual of the same species. Surface differences can cause donated cells or tissues to be recognised as foreign and therefore become targets of an immune response.