Helper T Cells: Structure, Activation, and Subsets in Immunology

What is the structure of the T cell receptor (TCR) complex?

The TCR complex consists of paired peptide chains (α and β or γ and δ) and is associated with CD3.

How can you identify a T helper cell?

A T helper cell can be identified by the presence of CD4 and its ability to recognize antigens displayed on MHC II.

What distinguishes T helper cells from cytotoxic T cells?

T helper cells (CD4+) recognize antigens on MHC II, while cytotoxic T cells (CD8+) recognize antigens on MHC I.

What is the role of costimulation in T cell activation?

Costimulation is necessary for T cell activation, as it provides additional signals that enhance the T cell response.

What are the main cytokines involved in the differentiation of T helper cells?

Cytokines such as IL-12, IL-4, and TGF-β play key roles in the differentiation of T helper cells into TH1, TH2, and TH17 subsets.

What are the three major subpopulations of helper T cells?

The three major subpopulations of helper T cells are TH1, TH2, and TH17.

What cytokines do TH1 cells secrete?

TH1 cells secrete interferon-γ (IFN-γ) and are stimulated by interleukin-12 (IL-12).

What is the primary function of TH2 cells?

TH2 cells primarily promote antibody responses and secrete cytokines such as IL-4, IL-13, and IL-10.

What is the role of TH17 cells?

TH17 cells promote neutrophil-mediated inflammation and secrete IL-17, stimulated by IL-6, TGF-β, and IL-23.

What is an immunological synapse?

An immunological synapse is the interface between a T cell and an antigen-presenting cell (APC) that facilitates communication and activation.

What is the significance of the SMAC in T cell activation?

SMAC (supramolecular activation clusters) organizes the interactions between T cells and APCs into a characteristic 'bull's eye' pattern.

What happens to T cell responses when indoleamine deoxygenase (IDO) is active?

IDO destroys tryptophan, leading to the termination of T cell responses.

What defines the type of T helper cell?

The type of T helper cell is defined by the cytokines it secretes, not by surface molecules.

What is the importance of the TCR/CD3 complex?

The TCR/CD3 complex is crucial for signal transduction and activation of T cells upon antigen recognition.

How do naïve TH cells differentiate into various subsets?

Naïve TH cells differentiate into TH1, TH2, TH17, or Treg based on signals received from APCs and the local environment.

What is the role of CD4 in T cell activation?

CD4 binds to MHC class II molecules on APCs, facilitating T helper cell activation.

What is the role of CD8 in T cell activation?

CD8 binds to MHC class I molecules on all nucleated cells, facilitating cytotoxic T cell activation.

What is the function of IL-2 in T cell responses?

IL-2 is a key cytokine that promotes T cell proliferation and survival.

What is the relationship between T cell subsets and microbial antigens?

Different antigens trigger the differentiation of naïve CD4+ T cells into distinct T helper subsets.

What is the predominant type of T cells in most mammals?

α/β Helper T cells are the predominant T cells in most mammals.

Where are γ/δ T cells primarily found in humans?

γ/δ T cells are mainly confined to the intestinal wall in humans.

What is the function of TH1 cells in immune responses?

TH1 cells activate macrophages and promote cell-mediated immune responses.

What cytokines are produced by TH2 cells and what are their functions?

TH2 cells produce IL-4, IL-13, and IL-10, which promote antibody responses.