Immune Response and Dendritic Cells Quiz

Antigen Presentation

• Antigen presentation is a crucial process for the immune system to recognize and respond effectively to foreign substances (antigens).
• T-lymphocytes recognize antigens only when displayed on MHC (Major Histocompatibility Complex) molecules on antigen-presenting cells (APCs).
• MHC molecules are essential for antigen presentation, binding and presenting antigens to T-cells.
• Antigen presentation ensures that the immune response is targeted specifically to the pathogen responsible for the infection. This highly specialized system is necessary to defend against pathogens.
• Different types of cells (e.g., dendritic cells, macrophages, and B cells) play important roles in capturing antigens, processing them, and presenting them to T lymphocytes.
• Antigen presentation is crucial for adaptive immunity; it initiates the adaptive immune response.
• The type and location of an antigen (e.g., cytosolic vs. vesicular) influences how the antigen is processed and presented.
• MHC molecules (class I and class II) have distinct roles in presenting antigens to T-cells.
• MHC class I displays peptides from intracellular proteins, while MHC class II displays peptides from extracellular proteins.

Learning Objectives

• Learning objectives for the lesson on Antigen Presentation include understanding how T and B lymphocytes recognize antigens.
• Knowing why the immune system requires specialized antigen presentation mechanisms for effective responses.
• Understanding what types of molecules play critical roles in antigen presentation to T lymphocytes.
• Defining "cross-presentation" while explaining how immune responses of CD8+ T lymphocytes are initiated by dendritic cells.
• Describing the molecular structure of MHC class I and II molecules, and the roles of the cells expressing them.
• Explaining the biological significance of MHC polymorphism.
• Understanding the roles of particular molecules found on T cells that contribute to their specificity for class I or class II MHC-associated peptide antigens.

Terms to be Familiar

• HLA (Human Leukocyte Antigen) is another name for MHC (Major Histocompatibility Complex).
• MHC molecules are proteins present on the surface of cells.
• Antigen-Presenting Cells (APCs) are cells that process antigens and display them to T lymphocytes.
• Naïve T lymphocytes are T-cells which have not encountered an antigen.
• Co-stimulation and co-stimulatory signals are essential for T-cell activation.
• Additional signals are needed for full activation of T lymphocytes.

Lymphocyte Differentiation

• Clonal expansion leads to the formation of effector cells and memory cells from lymphocytes.
• Different types of lymphocytes differentiate into effector cells, responsible for producing an immune response (e.g., antibody production, cytotoxic activity) and memory cells, responsible for secondary immune responses.
• Effector cells, such as antibody-producing plasma cells, cytotoxic T lymphocytes (CTLs), or helper T cells (TH cells), perform the tasks necessary for immediate immune responses.
• Memory lymphocytes ensure that your body can respond to future infections faster if the pathogen is encountered again.

Lymphocyte Repertoire

• The lymphocyte repertoire is the entire collection of possible lymphocyte specificities. This diversity is crucial for responding to a wide array of pathogens.
• Lymphocyte specificity is critical, enabling the immune system to target specific pathogens.
• The immune system has diversity to respond to a large variety of pathogens.
• The immune response is targeted at the specific pathogen based on the specificity of lymphocytes.
• The immune system has mechanisms for avoiding harm to the body by preventing reactions towards self-antigens for self-tolerance.

Rule 1

• Each lymphocyte of a clone has a unique antigen receptor for a specific antigen.

Rule 2

• T Lymphocytes recognize antigens only when they are presented by another cell on its surface with an MHC molecule.

Why Specialized Antigen Presentation

• Antigens can enter the body through various sites, requiring efficient methods to recognize and respond.
• Different types of antigens within the cytoplasm vs those inside vesicles require different responses from the immune system.
• The body needs different ways of reacting depending on the stage of the infection.
• Specialized systems for antigen capture and presentation are important because of the sheer volume of microbes the immune system must contend with.

Function of Dendritic Cells

• Dendritic cells (DCs) are specialized antigen-presenting cells.
• DCs capture antigens, process them, and migrate to lymph nodes to present antigens to lymphocytes.

Molecules That Play a Role in Antigen Presentation

• MHC molecules are crucial for antigen presentation to T lymphocytes. They present antigens to these lymphocytes and are the receptors recognized by the T cells
• Antigen-MHC complexes are displayed on the surface of APCs, allowing T-lymphocytes to recognize and respond.
• Individuals having different MHC molecules will have different responses to the same antigen. (MHC restriction)
• T lymphocytes use their T-cell receptors (TCRs) to recognize the presented antigen on an MHC molecule.

What Kind of Molecules Plays a Critical Role in Antigen Presentation

• MHC class I and class II molecules play a crucial role in antigen presentation to T lymphocytes.
• The T cell receptor (TCR) is the receptor that binds to the peptide-MHC complex.
• MHC molecules of the same individual will have specific peptide binding grooves
• T cells are specific to self-MHC.

B-Cell Antigen Recognition

• B lymphocytes recognize antigens directly using membrane-bound antibodies (immunoglobulins).
• These antibodies recognize various antigens (proteins, polysaccharides, etc.).
• Two forms of antibody exist : membrane-bound or secreted antibodies.

T-Cell Antigen Recognition

• T lymphocytes can recognize only peptides bound to MHC molecules on the surface of antigen-presenting cells.

Capture, Process, and Presentation of Antigens

• The three steps to antigen presentation are capturing, processing, and presenting to lymphocytes.
• Dendritic cells play a critical role in antigen capture and presentation.

MHC Molecules

• HLA (Human Leukocyte Antigen) are an alternative name for MHC (Major Histocompatibility Complex) molecules.
• MHC molecules are membrane proteins on antigen-presenting cells (APCs) that display peptide antigens to T-lymphocytes.
• Two major classes of MHC molecules exist class I and class II. Differences in peptide-binding grooves allow for varied antigen presentation

Structure of MHC I and II

• MHC class I and MHC class II molecules have distinctive structures for peptide binding. (Refer to page 34-35 for details regarding structure)
• The peptide-binding cleft determines the specific antigens each MHC molecule can present.

Polymorphism of MHC Molecules

• MHC polymorphism is crucial for the survival of the species because MHC varies across individuals in a population, thereby enabling better responses to diverse antigens.
• MHC molecules' varied ability to present specific antigens ensures that individuals have varied responses to distinct antigens, promoting species survival and adaptation.

Role of MHC Molecules in Effector Function

• MHC class II molecules are crucial for activating CD4+ helper T cells.
• MHC class I molecules are essential for activating CD8+ cytotoxic T lymphocytes which destroy infected cells.

Quiz Questions

• Refer to pages 56 for detailed questions and answers.

Test your understanding of the role of dendritic cells in the immune response. This quiz covers key functions, mechanisms of antigen capture, and factors influencing immunity. Challenge yourself with questions that explore the intricate workings of the immune system.