During the learning period, the drug would consistently lead to a suppression of the immune system. The rats now showed the same immune response in reaction to the saccharine solution alone. This finding shows that the immune system had learned to respond to a new stimulus and this learning had occurred via associative learning in the brain. Although researchers were initially skeptical about this finding, it was replicated several times, and provided the scientific basis for the now well-established field of psychoneuroimmunology. Methods in Human Research To study psychological influences on the immune system, it is important to assess the current status of the immune system.
Researchers use two approaches to measure the immune status of humans.
One method relies on counting of different immune cells. For example, researchers can draw blood and count the concentration of T, B, or NK cells in the blood stream. Often psychologists do not have ethical approval to draw blood. However, this does not mean that measuring the immune system is easy. Many methodological issues have to be considered.