To understand the current status of knowledge in the basic field of polarized specific
immune responses mediated by CD4+ T helper (Th) lymphocytes, based on their profile
of cytokine production (type 1 or Th1 and type 2 or Th2).
Relevant articles and publications from the medical literature, especially review
articles dealing with properties, mechanisms of polarization, transcription regulatory
factors, and role in different human pathophysiological conditions of Th1 and Th2
cells.
Th1 cells, which produce interferon (IFN)-gamma, interleukin (IL)-2 and tumor necrosis
factor (TNF)-beta, evoke cell-mediated immunity and phagocyte-dependent inflammation.
Th2 cells, which produce IL-4, IL-5, IL-6, IL-9, IL-10, and IL-13, evoke strong antibody
responses (including those of the IgE class) and eosinophil accumulation, but inhibit
several functions of phagocytic cells (phagocyte-independent inflammation). Both environmental
and genetic factors act in concert to determine the Th1 or Th2 polarization. Further,
Th1-dominated responses are involved in the pathogenesis of organ-specific autoimmune
disorders, Crohn's disease, sarcoidosis, acute kidney allograft rejection, and some
unexplained recurrent abortions. In contrast, allergen-specific Th2 responses are
responsible for atopic disorders in genetically susceptible individuals. Further,
Th2-dominated responses play a pathogenic role in both progressive systemic sclerosis
and cryptogenic fibrosing alveolitis, and favor a more rapid evolution of HIV infection
towards the full-blown disease. Finally, the Th1/Th2 paradigm can provide the basis
for the development of new types of vaccines against infectious agents and of novel
strategies for the therapy of allergic and autoimmune disorders.