Lock and Key to the Nth Degree. When any one of 'very many' intercellular 'blood borne' Activating Factors finds & fits-to a Cell Surface Receptor, this causes conformational changes to the...
Antibodies. For an naive B cell it is generally IgM and IgD. An activated B cell will express IgA, IgE or IgG after it goes through isotype switching.
glycoproteins
The receptor changes shape and activates a chain reaction that leads to the cell changing its activities.
target cells