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.
The second measure tests the effectiveness of immune cells in fighting a disease. For this purpose, researchers can test the activation, proliferation, transformation, and cytotoxicity of cells. The more proliferation, the better the immune system seems to handle the attack. In other words, it possesses immunocompetence . If the immune cells do not respond well to a mitogen, the immune system seems to be deficient.