What is the Difference Between TH1 and TH2 Helper Cells

The main difference between TH1 and TH2 helper cells is that the TH1 helper cells generate immune responses against intracellular parasites, including bacteria and viruses, whereas the TH2 helper cells generate immune responses against extracellular parasites including, helminths. Furthermore, TH1 helper cells produce interferon-gamma (INF-γ), interleukin-2 (IL-2), and tumor necrosis factor-beta (TNF-β) while TH2 helper cells produce interleukins including IL-4, IL-5, IL-6, IL-10, and IL-13.

The immune system produce two types of T helper cells as TH1 and TH2 helper cells.  The main function of T helper cells is to release cytokines, either to activate or suppress the other cells in the immune system.

Key Areas Covered

1. What are TH1 Helper Cells
     – Definition, Cytokines, Immune Response
2. What are TH2 Helper Cells
     – Definition, Cytokines, Immune Response
3. What are the Similarities Between TH1 and TH2 Helper Cells
     – Outline of Common Features
4,. What is the Difference Between TH1 and TH2 Helper Cells
     – Comparison of Key Differences

Key Terms

Cytokines, Immune Response, Interferon, Interleukin, TH1 Helper Cells, TH2 Helper Cells

What are TH1 Helper Cells

TH1 helper cells are the type of T helper cells produced by the immune system of the body, which generate immune responses against internal parasites including protozoa, bacteria and viruses. Internal parasites live inside the cells. When they infect antigen-presenting cells such as macrophages, dendritic cells, and B cells, their peptide antigens are expressed along with the MHC class II molecules on the surface of the antigen presenting cells. CD4 receptors on the TH1 cells recognize them.

Figure 1: TH1-Mediated Immunity

The INF-γ activate macrophages can kill infected cells through the phagocytic pathway. Moreover, INF-γ can trigger the direct killing of the protozoa and bacteria by activating free radicles. On the other hand, the cytokines produced by the TH1 helper cells trigger cell-mediated immune responses by activating cytotoxic T cells, and B cells. The overactivation of the TH1 helper cells may lead to hypersensitivity and autoimmunity.

What are TH2 Helper Cells

TH2 helper cells are the second type of T helper cells produced by the immune system of the body. They generate immune responses against external parasites including helminths. Generally, external parasites live outside the cells. Eosinophils are the major type of cells that kill helminths. The granules released by eosinophils activate and recruit dendritic cells to the point of infection, which in turn promote the development of TH2 helper cells’ response. In response to extracellular parasites, TH2 helper cells produce interleukins including IL-4, IL-5, IL-6, IL-10, and IL-13.

Figure 2: B cell Activation

The main effector cells of the cytokines produced by the TH2 helper cells are the B cells, which produce antibodies. On the other hand, the IL-5 activates eosinophils to kill helminths. Eosinophilia is the conditions with an increased number of eosinophils as a result of helminth infection. The IL-10 suppresses the development of TH1 helper cells.

Similarities Between TH1 and TH2 Helper Cells

• TH1 and TH2 helper cells are two types of T cells produced by the immune system.
• Both are lymphocytes produced in the bone marrow and their development occurs in the thymus.
• Also, the surface of the T helper cells contains a surface protein called CD4, a type of T cell receptors. Therefore, these cells are also called CD4+ T cells.
• Furthermore, they can recognize peptide antigens presented with the MHC class II molecules on the antigen presenting cells.
• Moreover, their main function is to produce cytokines upon the recognition of antigens to either activate or suppress the cells in the immune system.
• Besides, the cytokines produced by one type of T helper cells stimulate the production of T helper cells of the same type while inhibiting the production of T helper cells of the second type.

Difference Between TH1 and TH2 Helper Cells

Definition

TH1 helper cells refer to a type of T helper cells that generate immune responses against internal parasites while TH2 helper cells refer to a type of T helper cells that generate immune responses against external parasites. Hence, this is the bsic difference between TH1 and TH2 helper cells.

Transcription Factors

The development of TH1 helper cells is triggered by the transcription factors STAT4 and T-bet while the development of TH2 helper cells is triggered by the transcription factors STAT6 and GATA3.

Cell Differentiation

Another difference between TH1 and TH2 helper cells is that the differentiation of the TH1 helper cells is triggered by the IL-12 while the differentiation of the TH2 helper cells is triggered by the IL-4.

Type of Parasites

Moreover, another important difference between TH1 and TH2 helper cells is that the TH1 helper cells generate immune responses against protozoa, bacteria, and viruses while the TH2 helper cells generate immune responses against helminths.

Types of Cytokines Released

TH1 helper cells release INF-γ, IL-2, and TNF-β while TH2 helper cells release IL-4, IL-5, IL-6, IL-10, and IL-13. This is another difference between TH1 and TH2 helper cells.

Main Effector Cells

In addition, the main effector cells of the TH1 helper cells are macrophages, cytotoxic T cells, B cells while the main effector cells of the TH2 helper cells are the B cells.

Type of Immunity

Types of immunity they activate is also a major difference between TH1 and TH2 helper cells. TH1 cells mainly activate cell-mediated immunity while TH2 helper cells activate humoral immunity.

Overactivation

Finally, the overactivation of TH1 helper cells causes hypersensitivity and autoimmunity while the overactivation of TH2 helper cells causes allergy and hypersensitivity.

Conclusion

In breif, TH1 helper cells are the type of T helper cells that trigger immune responses against intracellular pathogens like protozoa and bacteria. They produce INF-γ, IL-2, and TNF-β. The major effector cells of the Th1 helper cells are macrophages, cytotoxic T cells, and B cells. Conversely, Th2 helper cells are the second type of T helper cells which trigger immune responses against extracellular pathogens like helminths. They produce interleukins including IL-4, IL-5, IL-6, IL-10, and IL-13. The main effector cells of TH2 helper cells are the B cells. The main difference between TH1 and TH2 helper cells is the type of immune response they generate.

Reference:

1. Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. Helper T Cells and Lymphocyte Activation. Available Here
2. Huang, Lu, and Judith A. Appleton. “Eosinophils in Helminth Infection: Defenders and Dupes.” Trends in parasitology 32.10 (2016): 798–807. PMC. Web. 9 Oct. 2018. Available Here

Image Courtesy:

1. “TransferFactors” By AaronMatthewWhite – Own work – From Aaron White’s self published book A Guide to Transfer Factors and Immune System Health (CC BY-SA 3.0) via Commons Wikimedia  
2. “TH2 and B cell interaction” By Becky Boone (CC BY-SA 2.0) via Flickr