To protect itself, the body uses both humoral immunity, which involves production of antibodies, and cellular immunity, which allows cell-mediated killing of infected or abnormal cells. Stimulation of humoral immunity against numerous infectious organisms has been achieved by vaccination using chemical adjuvants. However, manipulation of the cellular immune response has been more difficult.

T-helper cell differentiation determines the type of response a particular stimulus will elicit, and cytokines affect the differentiation of naive Th0 cells to either Th2 cells, which stimulate humoral immunity, or Th1 cells, which stimulate cellular immunity.