T-helper 1 cells vs. T-helper 2 cells

Attribute	T-helper 1 cells	T-helper 2 cells
Cytokine production	Interferon-gamma (IFN-γ)	Interleukin-4 (IL-4), Interleukin-5 (IL-5)
Function	Enhance cell-mediated immunity, activate macrophages	Enhance humoral immunity, activate B-cells
Associated diseases	Autoimmune diseases, chronic inflammation	Allergic diseases, asthma
Receptors	CD4, T-bet	CD4, GATA3
Response to antigens	Th1 response	Th2 response
Cellular targets	Macrophages, cytotoxic T-cells	B-cells, eosinophils

Introduction

T-helper cells, also known as CD4+ T cells, play a crucial role in the immune system by coordinating and regulating immune responses. They can be divided into different subsets, including T-helper 1 (Th1) cells and T-helper 2 (Th2) cells. While both subsets are involved in immune responses, they have distinct functions and characteristics. In this article, we will explore and compare the attributes of Th1 and Th2 cells.

Th1 Cells

Th1 cells are primarily involved in cell-mediated immunity, which is essential for defense against intracellular pathogens such as viruses and certain bacteria. These cells produce cytokines such as interferon-gamma (IFN-γ) and tumor necrosis factor-beta (TNF-β), which activate macrophages and enhance their ability to kill engulfed pathogens. Th1 cells also stimulate the production of cytotoxic T cells, which directly destroy infected cells.

Furthermore, Th1 cells promote the differentiation of B cells into plasma cells, leading to the production of antibodies, particularly of the IgG2a subclass. This subclass is crucial for opsonization and complement activation, further aiding in the elimination of intracellular pathogens. Th1 responses are typically associated with inflammation and are important in the clearance of chronic infections.

Th1 cells are primarily induced by interleukin-12 (IL-12) and interferon-gamma (IFN-γ), which are produced by antigen-presenting cells (APCs) such as dendritic cells and macrophages. These cells present antigens to naive CD4+ T cells, leading to their differentiation into Th1 cells. The transcription factor T-bet plays a critical role in the development and function of Th1 cells.

Th2 Cells

Th2 cells, on the other hand, are primarily involved in humoral immunity, which is important for defense against extracellular pathogens such as parasites and allergens. These cells produce cytokines such as interleukin-4 (IL-4), interleukin-5 (IL-5), and interleukin-13 (IL-13), which promote the activation and differentiation of B cells into plasma cells. Th2 responses are associated with the production of antibodies, particularly of the IgE subclass, which is involved in allergic reactions.

Th2 cells also recruit and activate eosinophils, which are important in the defense against parasites. Additionally, they stimulate the production of mucus and the contraction of smooth muscles, contributing to the expulsion of parasites from the body. Th2 responses are typically associated with tissue repair and allergic inflammation.

Th2 cells are primarily induced by interleukin-4 (IL-4), which is produced by mast cells, basophils, and other Th2 cells. IL-4 promotes the differentiation of naive CD4+ T cells into Th2 cells. The transcription factor GATA3 plays a critical role in the development and function of Th2 cells.

Comparison

While Th1 and Th2 cells have distinct functions, they also exhibit some overlapping characteristics. Both subsets are CD4+ T cells and express the CD4 co-receptor, which interacts with major histocompatibility complex class II (MHC-II) molecules on APCs. This interaction is crucial for antigen recognition and activation of T cells. Additionally, both subsets can produce cytokines that regulate immune responses.

However, Th1 and Th2 cells differ in their cytokine profiles and effector functions. Th1 cells primarily produce IFN-γ, TNF-β, and IL-2, which are involved in cell-mediated immunity and inflammation. In contrast, Th2 cells primarily produce IL-4, IL-5, and IL-13, which are involved in humoral immunity, tissue repair, and allergic inflammation.

Furthermore, the transcription factors involved in the development and function of Th1 and Th2 cells are distinct. Th1 cells are regulated by T-bet, while Th2 cells are regulated by GATA3. These transcription factors control the expression of cytokines and other molecules specific to each subset, further differentiating their functions.

Th1 and Th2 cells also exhibit different patterns of chemokine receptor expression, which influence their migration and localization within tissues. Th1 cells express CXCR3, allowing them to migrate towards sites of inflammation where the ligands for CXCR3, such as CXCL9 and CXCL10, are produced. In contrast, Th2 cells express CCR4 and CCR8, enabling their migration towards sites of allergic inflammation where the ligands for these receptors, such as CCL17 and CCL22, are produced.

Moreover, the differentiation of Th1 and Th2 cells is influenced by the cytokine milieu present during antigen presentation. IL-12 and IFN-γ promote Th1 differentiation, while IL-4 promotes Th2 differentiation. The balance between these cytokines determines the outcome of the immune response, with Th1 responses being favored in the presence of IL-12 and IFN-γ, and Th2 responses being favored in the presence of IL-4.

Conclusion

T-helper 1 (Th1) cells and T-helper 2 (Th2) cells are two distinct subsets of CD4+ T cells with different functions and characteristics. Th1 cells are involved in cell-mediated immunity and inflammation, while Th2 cells are involved in humoral immunity, tissue repair, and allergic inflammation. They differ in their cytokine profiles, effector functions, transcription factors, chemokine receptor expression, and differentiation requirements. Understanding the attributes of Th1 and Th2 cells is crucial for comprehending immune responses and developing targeted therapies for various diseases.