<unk>  is a secondary signal which immune cells rely on to activate an immune response in the presence of an antigen-presenting cell. In the case of T cells, two stimuli are required to fully activate their immune response. During the activation of lymphocytes,<unk>  is often crucial to the development of an effective immune response.<unk>  is required in addition to the antigen-specific signal from their antigen receptors.
Co-stimulation
Counterstimulation
Neural facilitation
Neural adaptation
Desensitization 
Neurostimulation
Microstimulation
Neuroenhancement