What are T helper 1 (Th1) and T helper 2 (Th2) lymphocytes?

From the Guidelines

T helper 1 (Th1) and T helper 2 (Th2) lymphocytes are two subsets of CD4+ T cells that play crucial roles in the immune system, with Th1 cells secreting cytokines that promote cell-mediated immunity and Th2 cells secreting cytokines that promote humoral immunity.

Key Characteristics of Th1 and Th2 Cells

• Th1 cells are involved in cell-mediated immunity, secreting cytokines such as interferon-gamma (IFN-γ) that activate macrophages and promote the killing of intracellular pathogens 1.
• Th2 cells are involved in humoral immunity, secreting cytokines such as interleukin-4 (IL-4) that stimulate B cells to produce antibodies 1.

Role in Disease

• Imbalances in Th1 and Th2 responses have been implicated in various diseases, including autoimmune disorders and allergic reactions 1.
• Th1 cells have been shown to play a role in the pathogenesis of psoriasis, with Th17 cells also contributing to the disease 1.
• Th2 cells have been implicated in the development of allergic diseases, such as asthma and atopic dermatitis 1.

Importance in Clinical Medicine

• Understanding the roles of Th1 and Th2 cells is essential for the development of effective treatments for various diseases, including autoimmune disorders and allergic reactions 1.
• CD4+ T-cell determinations, which include Th1 and Th2 cells, are important for monitoring immune function in individuals with HIV infection 1.

From the Research

Definition of T Helper 1 (Th1) and T Helper 2 (Th2) Lymphocytes

• T helper 1 (Th1) and T helper 2 (Th2) lymphocytes are functionally distinct helper T (Th)-cell subsets characterized by the patterns of cytokines they produce 2, 3.
• Th1 cells produce interleukin (IL)-2, gamma-interferon (IFN-gamma), and tumour necrosis factor-beta, whereas Th2 cells express IL-4, IL-5, IL-6, and IL-10 3.

Functions of Th1 and Th2 Cells

• Th1 cells induce delayed-type hypersensitivity reactions and are effective in eradicating infectious agents, including those hidden within the host cells 2, 4.
• Th2 cells are excellent helpers for B-cell antibody secretion, particularly IgE responses, and provide some protection against parasites 2, 3.
• Th2 cells can also limit potentially harmful Th1-mediated responses and are involved in the pathogenesis of atopic disorders and some systemic autoimmune diseases 2, 5.

Factors Influencing Th1 and Th2 Polarization

• The development of polarized Th1 or Th2 responses depends on environmental factors, including the dose of antigen, nature of immunogen, and cytokines (IL-12 and interferons or IL-4) at the time of antigen presentation 2.
• Genetic factors, such as the individual's genetic background, can also influence Th1 and Th2 polarization 2, 5.
• Other factors, such as the activity of costimulatory molecules and microenvironmentally secreted hormones, can also influence Th cell differentiation into the polarized Th1 or Th2 pathway 5.

Role of Th1 and Th2 Cells in Human Diseases

• 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 4, 5.
• Th2-dominated responses are responsible for atopic disorders, progressive systemic sclerosis, cryptogenic fibrosing alveolitis, and favor a more rapid evolution of HIV infection towards the full-blown disease 4, 5.