Immunology Lecture 2-5 (2024)

Which of the following cytokines is NOT involved in the differentiation of Th17 cells?

What is the primary function of Th2 cells?

Which type of T cell is involved in suppressing stimulatory activity of APCs?

What is the primary function of CD8+ T cells?

Which cytokine is involved in the differentiation of Th1 cells?

What is the role of TGF-β in the differentiation of Treg cells?

Which cells display peptides in the context of highly polymorphic MHC molecules?

What is required for the activation of T cells?

What is the primary function of CD8 T cells?

What is required for the activation of CD4 T cells?

What is the function of MHC class I molecules?

What is the result of T cell receptor genes undergoing rearrangements?

What is the function of co-stimulatory molecules such as CD28 and CD86?

What is the difference between MHC class I and II molecules?

What is the result of the interaction between the T cell receptor and MHC molecules?

What is the characteristic of T cell receptors?

What is the function of antigen-presenting cells (APCs) such as monocytes, macrophages, and dendritic cells?

What is the result of the activation of CD4 T cells?

T Cell Antigen Recognition

• Peptides are displayed by cells in the context of highly polymorphic MHC molecules.
• MHC molecules are highly polymorphic, with MHC I and II having different structures and functions.
• MHC I is expressed on all nucleated cells, associates with β2 microglobulin, and is endogenously expressed.
• MHC II is expressed on specialized antigen-presenting cells (APCs), including monocytes, macrophages, dendritic cells, and B lymphocytes.

Sources of Peptides Loaded into MHC Class I and II

• MHC class I is loaded with peptides from viral proteins and endogenous proteins.
• MHC class II is loaded with peptides from exogenous antigens.

T Cells Recognise Peptides with Their T Cell Receptors

• T cells are defined by expression of the T cell receptor (TCR), which is a membrane-bound heterodimer.
• TCR consists of two chains (α and β) joined by disulfide bonds, with variable and constant domains.
• TCR genes undergo rearrangements from germline before translation.

Two Main Classes of ab T Cell

• CD8+ T cells (cytotoxic T cells) recognise peptides presented by MHC I.
• CD4+ T cells (helper T cells) recognise peptides presented by MHC II.

Activation of T Cells Requires Two Signals

• Signal 1: TCR recognises peptide-MHC complex.
• Signal 2: Co-stimulation by CD28 and CD86, which is upregulated on APCs by danger signals (infection, inflammation).

CD8 T Cells: Cytotoxic Lymphocytes (CTL)

• CD8+ T cells are cytotoxic cells that can kill target cells, such as virus-infected cells or cancerous cells.

Activated CD4 Cells Can Differentiate into Different Kinds of Effector T Cells

• CD4+ T cells can differentiate into different types of helper T cells, including Th1, Th2, Th17, and Treg cells.
• Each type of helper T cell has distinct functions, such as producing different cytokines and providing help to different cells.

CD4+ T Cell Subsets

• Th1 cells: produce IFN-γ and IL-2, help activate CD8+ T cells and macrophages.
• Th2 cells: produce IL-4, IL-5, and IL-13, help activate B cells.
• Th17 cells: produce IL-17, IL-21, and IL-22, help fight extracellular pathogens.
• Treg cells: produce TGF-β and IL-10, suppress immune responses.

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