The immune response is a specific response to the detection of pathogens in the body. It involves a coordinated response between a wide range of cells. In order to work together effectively, these cells need to communicate. This is known as cell signalling.
This communication is achieved through cell surface molecules and the release of hormone like chemicals called cytokines. In order to detect a signal, the target cell must have a cell surface receptor. B lymphocytes (B cells) and T lymphocytes (T cells) have receptors that are complimentary in shape to the foreign antigen. The antigen may be an isolated protein, it may be attached to a pathogen, or it may be on the surface of a host cell. When the antigen is detected, the lymphocyte is activated or stimulated. Chemical signals are also detected by their target cells using specialised cell receptors.
What sort of information is communicated?
The first signalling is actually done by the pathogen. The pathogen carries antigens on its cell surface. These act as flags or markers that say “I am foreign”. These are detected by our body cells.
Sending distress signals:
When a body cell is infected by a pathogen, it is usually damaged in some way. The internal cell organelles such as Lysosomes will attempt to fight the invader. As a result, a number of pathogen cells are damaged. Parts of the pathogen often end up attach to the host plasma membrane. These have two effects: