Cytokines in Pathogen Infection and Autoimmune Disease

Immune responses have long been classified into T helper (Th)1, Th2, and Th17, with different Th type immune cells classified according to the cells that secrete specific cytokines. However, careful examination of cytokine production allows distinction between Th1 and Th2 depending on the type of infectious pathogen. For instance, Th1 cytokines are produced after intracellular pathogens such as intracellular bacteria, viruses, and protozoa whereas Th2 cytokines are produced after extracellular pathogens such as multicellular parasites. Autoimmune diseases are caused by chronic inflammation due to overproduction of Th1 or Th2 cytokines without a clear cause, but are related to aging, genetic factors, and environmental factors. This brief review explores the regulation of immune responses by cytokines, outlining potential theories for understanding infectious and inflammatory autoimmune diseases.