What is the Difference Between TH1 and TH2 Immune Response

The main difference between TH1 and TH2 immune response is that TH1 immune response is a proinflammatory response, which kills intracellular parasites and perpetuates autoimmune responses, whereas TH2 immune response promotes IgE and eosinophilic responses in atopy and produces anti-inflammatory responses, which kill large, extracellular parasites such as helminths. Furthermore, TH1 cytokine is the interferon gamma while TH2 cytokines include interleukin 4, 5, 10, and 13.  

TH1 and TH2 immune response are the two types of immune responses generated by T helper cells. Both immune responses are mediated by cytokines.  

Key Areas Covered 

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

Key Terms 

Anti-Inflammatory Response, CD4 T Cells, CD8 T Cells, Cytokines, Interferons, Interleukins, Proinflammatory Response, TH1, TH2, T Helper Cells

What is the TH1 Immune Response 

TH1 immune response is the immune response generated by TH1 cells against intracellular parasites like bacteria and virus. Generally, the polarising cytokine IL-12 is responsible for triggering the TH1 immune response by activating TH1 cells. Furthermore, the activated TH1 cells secrete cytokines such as interferon-gamma (IFN-γ) and interleukin-2 (IL-2). TH1 immune response is a proinflammatory response that leads to cell-mediated immunity. Therefore, it activates macrophages as well as CD8 T cells, IgG B cells, and IFN-γ CD4 T cells.

Figure 01: T Helper Cell

Here, the activated macrophages phagocytose and digest intracellular bacteria and protozoa. Also, IFN-γ activates iNOS to produce NOx free radicals to directly kill intracellular bacteria and protozoa. However, the overactivation of the TH1 immune response can recognize self-antigens, causing Type 4 delayed-type hypersensitivity, a category of autoimmunity.  

What is the TH2 Immune Response 

TH2 immune response is the immune response TH2 cells generate against extracellular parasites such as helminths. Here, the polarizing cytokines, including IL-4 and IL-2, trigger the TH2 immune response by activating TH2 cells. Then, the activated TH2 cells secrete cytokines, including IL-4, IL-5, IL-9, IL-10, IL-13, and IL-25.

Figure 2: T Helper Cell Function

Moreover, the TH2 immune response is an anti-inflammatory response, which leads to the humoral immune response. That means; IL-4 stimulates B-cells to produce IgE antibodies. These antibodies, in turn, stimulate mast cells to release histamine, serotonin, and leukotriene, causing broncho-constriction, intestinal peristalsis, gastric fluid acidification to expel helminths. Moreover, IL-5 activate eosinophils to attack helminths. Also, IL-10 suppresses Th1 cells differentiation and the action of dendritic cells. 

Similarities Between TH1 and TH2 Immune Response 

• TH1 and TH2 immune response are two types of immune responses generated by T Helper cells that contain the surface receptor, CD4. 
• Both fight against infectious diseases by producing cytokines, which activate or suppress the function of other cells in the immune system. 
• Therefore, both types of immune responses are a part of the adaptive immunity. 

Difference Between TH1 and TH2 Immune Response 

Definition 

TH1 immune response refers to the cytokine-mediated immune response generated by TH1 cells against intracellular parasites such as bacteria and virus, while TH2 immune response refers to the cytokine-mediated immune response generated by TH2 cells against large, extracellular parasites such as helminths. Thus, this is the main difference between TH1 and TH2 immune response.

Type of T Helper Cells 

TH1 cells generate TH1 immune responses, while TH2 cells generate TH2 immune responses. 

Triggered By 

The polarising cytokine IL-12 is responsible for triggering TH1 immune responses, while the polarizing cytokines, including IL-4 and IL-2, trigger TH2 immune responses. Hence, this is another difference between TH1 and TH2 immune response.

Type of Cytokines Produced 

Cytokines produced by TH1 cells including interferon-gamma (INF-γ), interleukin-2 (IL-2), and tumor necrosis factor-beta (TNF-β) mediate TH1 immune responses, while cytokines produced by TH2 cells such as interleukins (IL-4, IL-5, IL-6, IL-10, and IL-13) mediate TH2 immune responses. 

Effector Cells 

Moreover, the effector cells contribute to another difference between TH1 and TH2 immune response. The former activates macrophages as well as CD8 T cells, IgG B cells, and IFN-γ CD4 T cells while the latter activates mast cells, eosinophils, dendritic cells, etc.

Type of Immune Response 

Also, the TH1 immune response is a proinflammatory response and perpetuates autoimmune responses, while TH2 immune response promotes IgE and eosinophilic responses in atopy and produces anti-inflammatory responses. 

Act Against 

Furthermore, TH1 immune responses act against intracellular parasites such as bacteria and virus while TH2 immune responses act against large, extracellular parasites such as helminths. 

Type of Adaptive Immunity 

While TH1 immune response leads to cell-mediated immunity, TH2 immune response leads to humoral immunity. 

Autoimmune Response 

Importantly, excessive TH1 immune responses lead to the uncontrolled tissue damage by autoimmune responses, while TH2 immune responses counteract TH1 immune responses. 

Conclusion 

TH1 immune response is the immune response generated by the TH1 cells. It occurs through the production of cytokines, including interferon-gamma. Moreover, it is a type of proinflammatory response, which leads to cell-mediated immunity. However, the TH1 immune response acts against intracellular parasites such as bacteria and virus. Additionally, it generates autoimmune responses, as well. On the other hand, TH2 immune response is the immune response generated by TH2 cells. It occurs through the production of cytokines such as interleukin 4, 5, 10, and 13. Moreover, it generates an anti-inflammatory response, which leads to a humoral immune response. TH2 immune response also acts against large, extracellular parasites. Therefore, the main difference between TH1 and TH2 immune response is the type of inflammatory response generated by each immune response. 

References:

1. Berger, A. “Th1 and Th2 responses: what are they?.” BMJ (Clinical research ed.) vol. 321,7258 (2000): 424. doi:10.1136/bmj.321.7258.424

Image Courtesy:

1. “1123292” By allinonemovie (Pixabay License) via Pixabay
2. “Lymphocyte activation” By Mikael Häggström. (Public Domain) via Commons Wikimedia