Introduction
Right at the beginning of this module, we told you that the adaptive immune cells need to know exactly what or who to fight, as they don't fight blindly, and that the exact message of who to fight needs to be delivered in a special package by a cell that the adaptive immune cells trust. We now know that the message comes in the form of a peptide derived from the pathogen and how it is generated. We also know that the special package is MHC that associates with the peptide and we know that the trusted cells are our antigen presenting cells that all have individual special features. There are other factors that influence how well this message of threat is delivered to the adaptive immune cells, for example, the presence of costimulatory and adhesion molecules and cytokines that the APC secretes while talking to the adaptive immune cells. Just like turning up the volume and adjusting the treble and base on your radio affects how well you receive the broadcasted message, the levels of these surface molecules and the range of cytokines released affects how the adaptive immune cell receives the message of threat. Whereas you make all the adjustments to your radio, the things present in the environment at the time when the APC takes up the antigen, affect the APC to fine tune the levels of surface molecules and cytokines released. This is very well exemplified by the DC, which is why we have chosen this APC to highlight what in the environment affects APCs and how they consequently react.
When you are working your way through the next few pages of this module, try thinking about what was making the change in the DC, how the DC changed and if you think this change will make the T cell get the message better or worse?