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Which phenomenon increases the production of antibodies in B-cells?
Which phenomenon increases the production of antibodies in B-cells?
What is the primary function of the CD8 molecule in T-cells?
What is the primary function of the CD8 molecule in T-cells?
Which of the following describes the role of perforin in cell-mediated immunity?
Which of the following describes the role of perforin in cell-mediated immunity?
What describes the condition where immune cells do not react against the body’s own tissues?
What describes the condition where immune cells do not react against the body’s own tissues?
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What is the result of T-helper cells releasing IL-6 and IL-5?
What is the result of T-helper cells releasing IL-6 and IL-5?
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What is the primary role of chemokines released by cells in lymph nodes?
What is the primary role of chemokines released by cells in lymph nodes?
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Which cytokine is primarily responsible for the autocrine stimulation of T-cells?
Which cytokine is primarily responsible for the autocrine stimulation of T-cells?
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What is the significance of the interaction between LFA-1 and ICAM-1?
What is the significance of the interaction between LFA-1 and ICAM-1?
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Which statement accurately describes humoral immunity?
Which statement accurately describes humoral immunity?
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What is the role of IL-2 in T-cell activation?
What is the role of IL-2 in T-cell activation?
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What is one function of granzymes released by cytotoxic T-cells?
What is one function of granzymes released by cytotoxic T-cells?
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Which cell type interacts with MHC-II molecules during the activation process?
Which cell type interacts with MHC-II molecules during the activation process?
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How do T-helper cells contribute to the activation of B-cells?
How do T-helper cells contribute to the activation of B-cells?
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What is the function of peripheral tolerance in the immune system?
What is the function of peripheral tolerance in the immune system?
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In which scenario would cell-mediated immunity primarily be engaged?
In which scenario would cell-mediated immunity primarily be engaged?
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Which molecules are important for the adhesion of T-cells to high endothelial venules?
Which molecules are important for the adhesion of T-cells to high endothelial venules?
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What activates proapoptotic genes?
What activates proapoptotic genes?
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What do cytochrome C and caspases lead to?
What do cytochrome C and caspases lead to?
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What is humoral immunity primarily concerned with?
What is humoral immunity primarily concerned with?
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What cells activate B cells in humoral immunity?
What cells activate B cells in humoral immunity?
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What are cytotoxic T cells responsible for?
What are cytotoxic T cells responsible for?
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Natural killer cells are part of the adaptive immune system.
Natural killer cells are part of the adaptive immune system.
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What are endogenous molecules?
What are endogenous molecules?
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Adaptive immunity consists of __ and __ immunity.
Adaptive immunity consists of __ and __ immunity.
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What is the first signal that activates B cells?
What is the first signal that activates B cells?
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What process do B cells undergo when they start dividing?
What process do B cells undergo when they start dividing?
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What is produced when B cells differentiate due to interleukin 5?
What is produced when B cells differentiate due to interleukin 5?
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What type of antibodies can B cells produce?
What type of antibodies can B cells produce?
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What happens during the process of neutralization by antibodies?
What happens during the process of neutralization by antibodies?
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What is opsonization?
What is opsonization?
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What type of immunity is primarily responsible for the activation of B cells by free antigens?
What type of immunity is primarily responsible for the activation of B cells by free antigens?
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What proteins do cytotoxic T cells produce to kill infected or cancerous cells?
What proteins do cytotoxic T cells produce to kill infected or cancerous cells?
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What is the main function of natural killer cells?
What is the main function of natural killer cells?
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What are the components on the surface of antigen presenting cells?
What are the components on the surface of antigen presenting cells?
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What triggers the activation of a naive B cell?
What triggers the activation of a naive B cell?
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Cluster differentiation protein four (CD4) is found on all T cells.
Cluster differentiation protein four (CD4) is found on all T cells.
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The process by which a naive T cell becomes activated requires ________ signals.
The process by which a naive T cell becomes activated requires ________ signals.
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What is the role of interleukin-2 in T cell activation?
What is the role of interleukin-2 in T cell activation?
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Which type of cell can undergo receptor-mediated endocytosis?
Which type of cell can undergo receptor-mediated endocytosis?
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What do MHC II molecules present to T cells?
What do MHC II molecules present to T cells?
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To differentiate into a T helper 2 cell, a naive T cell needs stimulation from ________.
To differentiate into a T helper 2 cell, a naive T cell needs stimulation from ________.
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B cells can directly recognize and bind to free antigens without activation.
B cells can directly recognize and bind to free antigens without activation.
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What do naive T helper cells require for their activation?
What do naive T helper cells require for their activation?
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What happens to the B lymphocyte after it is activated?
What happens to the B lymphocyte after it is activated?
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Study Notes
Adaptive Immune System
- The adaptive immune system is a specific, choreographed defense system, unlike the innate immune system, which is non-specific.
Components of the Adaptive Immune System
- Lymphoid tissues
- Circulating effector proteins
- Inflammatory cytokines
- Effector cells
Lymphoid Tissues
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Lymph nodes
- Sites where immune cells interact.
- For oral cavity: tonsils and adenoids.
- Cells within lymph nodes produce chemokines to attract dendritic cells.
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Spleen
- Contains macrophages to clean up red blood cells (RBCs) and infections.
Mechanical Barriers
- Skin
- Mucous membranes
- Normal flora
Circulating Effector Proteins
- Antibodies
- Complement proteins
- Cytokines
Inflammatory Cytokines
- IL-1: Produced by macrophages.
- IL-2: Autocrine cytokine produced by T cells, promoting T cell proliferation.
- IL-4: Secreted by T cells, responsible for B cell clonal expansion and differentiation.
- IL-5: Secreted by T cells, induces B cell differentiation into plasma or memory B cells.
- IL-6: Secreted by T cells, promotes plasma cell production and antibody secretion.
- CXCL10: A chemokine that attracts T cells to sites of infection.
- Granzymes: Cytotoxic T cell-derived enzymes that activate pro-apoptotic genes in infected cells.
- Perforin: A cytotoxic T cell-derived protein that forms pores in infected cell membranes.
Effector Cells
- Macrophages: Phagocytic cells that engulf pathogens and present antigens to other immune cells.
- Dendritic Cells: Antigen-presenting cells that activate T cells.
- B Lymphocytes (B Cells): Produce antibodies that neutralize pathogens.
-
T Lymphocytes (T Cells): Coordinate immune responses and directly kill infected cells.
- T Helper Cells (Th cells): Release cytokines that activate other immune cells (e.g., B cells and macrophages).
- Cytotoxic T Cells (Tc cells): Kill infected cells.
- Plasma cells: Differentiated B cells that secrete antibodies.
- Memory B cells: Long-lived B cells that provide lasting immunity.
Properties of Adaptive Immune Cells
- Specificity: Recognize and target specific antigens.
- Memory: Remember past encounters with antigens to mount faster and more effective responses.
- Self-tolerance: Immune cells are tolerant to body's own tissues to prevent autoimmune diseases.
Peripheral Tolerance
- Occurs in lymphoid tissues to ensure self-tolerance.
Humoral Immunity
-
Receptors:
- B Lymphocytes: Antigens bind to B cell receptors (BCRs).
- Macrophages: Antigens are displayed on Major Histocompatibility Complex (MHC) II molecules.
- Naive T helper cells: Antigens are displayed on MHC II molecules.
- Cytotoxic T cells: Antigens are presented on MHC I molecules.
-
Cytokines:
- IL-1: Released by macrophages.
- IL-2: Released by T cells.
- IL-4: Released by T cells, promoting B cell clonal expansion and differentiation.
- IL-5: Released by T cells, causing B cell differentiation into plasma or memory B cells.
- IL-6: Released by T cells, causing plasma cells to secrete antibodies.
-
Antibodies:
- Bind to pathogens and neutralize them.
- Can activate complement cascade, leading to pathogen lysis.
Cell Mediated Immunity
-
Apoptosis: Programmed cell death of infected cells.
- Caspase activation: A cascade of enzymes that dismantle the cell.
- DNA fragmentation: Nucleic acids are broken down.
- Cell shrinkage: The cell shrinks and forms blebs, which are phagocytosed by macrophages.
Antigen Presentation
- Exogenous pathway: Antigens are presented on MHC II molecules, generally by macrophages or dendritic cells, to T helper cells.
- Endogenous pathway: Antigens are presented on MHC I molecules, generally by infected cells or cancerous cells, to cytotoxic T cells.
Interactions
- CD28: T cell receptor, interacts with B7 on macrophages.
- CD8: T cell receptor, interacts with MHC I.
- CD4: T cell receptor, interacts with MHC II.
- LFA-1: Adhesion molecule on T cells, interacts with ICAM-1 on high endothelial venules.
- VLA-4: Adhesion molecule on T cells, interacts with VCAM on high endothelial venules.
- CXCR3: Chemokine receptor on T cells, interacts with CXCL10 chemokine.
- E/P selectin ligand: Adhesion molecule on T cells, interacts with E/P selectin on endothelial cells.
T Helper Cell Roles
- Th1 cells: Promote cell-mediated immunity.
- Th2 cells: Promote humoral immunity and allergic responses.
IL-4 and IL-5 Roles
- IL-4: Induces B cell proliferation and differentiation.
- IL-5: Active B cells and promotes differentiation of B cells into plasma or memory B cells.
Antibody Effects
- Neutralization: Prevent pathogen from binding to host cells.
- Opsonization: Enhances phagocytosis.
- Complement activation: Lyses pathogens and amplifies inflammation.
- Antibody-dependent cell-mediated cytotoxicity (ADCC): Recruits NK (natural killer) cells to destroy pathogens.
- Agglutination: Clump pathogens together.
Adaptive Immune System Components
- Adaptive immunity is specific and involves coordinated defenses unlike innate immunity which uses physical barriers and non-specific defenses.
- Lymph nodes are the primary sites for the adaptive immune response and contain specialized cells, including macrophages, dendritic cells, T lymphocytes, and B lymphocytes.
- Certain lymph nodes are specialized for specific body regions, for example, the tonsils and adenoids are the lymph nodes for the oral cavity.
- The spleen is another essential organ in the adaptive immune system that contains macrophages to remove damaged red blood cells and fight infections.
- Circulating effector proteins like antibodies, complement proteins, and cytokines are key players in the adaptive immune response.
- Inflammatory cytokines like IL-1, IL-6, TNF-α, IFN-γ, and chemokines like CXCL10 are involved in attracting immune cells, activating other immune cells, and amplifying the immune response.
- Effector cells include lymphocytes (T cells and B cells), macrophages, neutrophils, and dendritic cells.
- T-helper cells recognize antigens presented by Antigen Presenting Cells (APCs) and then differentiate into subtypes like Th1 and Th2.
- Th1 cells help activate macrophages and cytotoxic T cells to target intracellular pathogens.
- Th2 cells help activate B cells to produce antibodies against extracellular pathogens.
- Cytotoxic T-cells directly kill infected cells through the release of granzymes and perforin, which trigger apoptosis.
Properties of Adaptive Immune Cells
- Cells in the adaptive immune system have the capability to differentiate and proliferate in response to specific antigens.
- Non-reactivity to self is ensured through peripheral tolerance that develops in lymphoid tissues.
Humoral Immunity
- In humoral immunity, B lymphocytes are responsible for producing antibodies.
- B-cell receptors (BCRs) recognize specific antigens and are present on the surface of B lymphocytes.
- Macrophages have receptors for antibodies and can help in phagocytosing antigens tagged with antibodies.
- Naive T-helper cells have receptors for MHC II molecules and can become activated by antigens presented by APCs.
- Cytotoxic T cells have receptors for MHC I molecules and can recognize and kill infected cells.
- IL-1 is released by macrophages, IL-2 (autocrine) is released by T-cells, while T-cells also release IL-4 (clonal expansion of B-cells), IL5 (B-cell differentiation), IL-6 (plasma cell antibody production), and IL5 (plasma cell antibody production).
- In cell-mediated immunity, cytotoxic T cells use granzymes and perforin to induce apoptosis in infected cells.
- Viral infected cells release proteins like BAX and BCL2 that lead to the release of cytochrome C triggering apoptosis.
- Interaction proteins are crucial for T-cell activation and include CD28 and B7 (macrophage); CD8 and MHC-I; CD4 and MHC-II; LFA-1 and ICAM-1 (high endothelial venule); VLA-4 and VCAM (high endothelial venule); CXCR3 and CXCL10 (chemokine); and E/P selectin ligand and E/P selectin.
- T-helper cells can differentiate into Th1 or Th2 cells, which mediate distinct immune responses.
- IL-4 promotes clonal expansion of B-cells, while IL-5 activates B-cells and helps differentiate them into plasma cells (which secrete antibodies) or memory B-cells.
- Antibodies may neutralize the antigen, opsonize the antigen, or activate complement, leading to pathogen elimination.
Cell Mediated Immunity
- Cell-mediated immunity is an immune response that is mediated by T-cells, which directly kill infected cells or stimulate other immune cells.
- Cancerous cells and virally infected cells are targeted by the cell-mediated immune response.
- Apoptosis is a programmed cell death process that is triggered by cytotoxic T cells through the release of granzymes and perforin, which cause the infected cell to undergo apoptosis.
- Apoptosis is achieved through the activation of pro-apoptotic genes, leading to the release of mitochondrial proteins like cytochrome C.
Adaptive Immunity Overview
- Adaptive immunity is a specific immune response that targets particular pathogens or antigens.
- This response is initiated within the lymph nodes, where antigen presenting cells (APCs) interact with lymphocytes, stimulating an immune response.
Antigen Presenting Cells (APCs)
- Macrophages engulf pathogens and present antigens on their cell surface using MHC II molecules.
- Dendritic cells are highly specialized APCs that migrate to lymph nodes to present antigens to T cells.
Lymph node Structure and Function
- Lymph nodes house immune cells, including B cells, T cells, macrophages, and dendritic cells.
- Germinal centers within lymph nodes are enriched with B cells that are responsible for antibody production.
B Cells and B Cell Receptor (BCR)
- B lymphocytes (B cells) are responsible for antibody production.
- B cell receptors (BCRs) are surface-bound antibodies (IgD) that recognize specific antigens.
- Each B cell possesses unique BCRs due to genetic recombination, allowing for a diverse repertoire of antigen recognition.
B Cell Activation
- When an antigen binds to a BCR, it triggers receptor-mediated endocytosis, internalizing the antigen-antibody complex.
- The B cell then presents the antigen on its surface via MHC II molecules, becoming an APC.
T Cell Activation
- Naive T helper cells express CD4 receptors and TCRs, which recognize MHC II-antigen complexes.
- The interaction between the T cell receptor and the MHC II-antigen complex on the APC initiates the activation of the naive T helper cell.
Co-Stimulation
- Co-stimulation is essential for complete T cell activation.
- B7 molecules on the APC interact with CD28 on the naive T helper cell, triggering co-stimulation.
Interleukin 1 (IL-1)
- Interleukin 1 (IL-1), secreted by the APC, binds to receptors on the naive T helper cell, providing a third signal for activation.
T Helper (Th) Cell Differentiation
- Activated naive T helper cells can differentiate into Th1 or Th2 cells, depending on the cytokine environment.
- IL-4 promotes differentiation into Th2 cells.
- IL-12 promotes differentiation into Th1 cells.
Th2 Cell Function
- Th2 cells secrete IL-4 and IL-5.
B Cell Proliferation and Differentiation
- IL-4 secreted by Th2 cells activates the activated B cell, triggering clonal expansion.
- Clonal expansion results in the production of a large number of B cells with specific BCRs.
- IL-5, secreted by Th2 cells, promotes the differentiation of B cells into plasma cells, which are the primary antibody-producing cells.
B Cell Differentiation
- Interleukin 5 (IL-5) stimulates the differentiation of clonally expanded B cells into plasma cells and memory B cells.
- Plasma cells are responsible for secreting antibodies.
- Memory B cells are long-lived cells that retain the ability to produce antibodies specific to the foreign antigen they encountered.
- Interleukin 6 (IL-6) stimulates plasma cell formation.
- IL-5 and IL-6 stimulate antibody secretion by plasma cells.
Antibody Function
- Antibodies are proteins that bind specifically to foreign antigens.
- Antibodies can neutralize pathogens by blocking their ability to attach to host cells.
- Antibodies can also cause precipitation of antigens, potentially leading to type 3 hypersensitivity reactions when antigen-antibody complexes deposit in tissues.
- Antibodies can activate the complement system, leading to the formation of a membrane attack complex (MAC) that lyses cells.
- Antibodies can agglutinate red blood cells, which can be problematic in mismatched blood transfusions.
- Antibodies can opsonize pathogens, making them more easily recognizable and phagocytized by macrophages.
Humoral Immunity
- Humoral immunity is a component of adaptive immunity that involves the production of antibodies by B cells.
- Humoral immunity is triggered by exogenous antigens, meaning those found outside of cells in bodily fluids, such as the bloodstream.
- B cells differentiate into plasma cells, producing antibodies that target the specific antigen that initially triggered the immune response.
Cellular Immunity
- Cellular immunity, also a component of adaptive immunity, is a response to antigens that are inside of infected cells.
- This type of response involves cytotoxic T cells.
- Cytotoxic T cells are known for their role in eliminating cells infected with viruses or cancerous cells.
Understanding Cell-Mediated Immunity: The Role of MHC Class I and TCR
- Infected or cancerous cells present processed antigens on MHC Class I molecules.
- These MHC Class I molecules with their bound antigens become "targets" for cytotoxic T cells.
- Cytotoxic T cells have a T cell receptor (TCR) that recognizes specific MHC Class I- antigen complexes.
How Cytotoxic T Cells Eliminate Infected or Cancerous Cells
- When a cytotoxic T cell encounters a cell expressing a MHC Class I molecule with a foreign antigen complex it recognizes, it releases perforin and granzymes.
- Perforin forms pores in the membrane of the target cell, allowing granzymes to enter.
- Granzymes activate pro-apoptotic genes, leading to the activation of caspase and the initiation of the programmed cell death pathway (apoptosis).
Apoptosis: The Mechanism of Programmed Cell Death
- Apoptosis is a process that involves the breakdown of the cell's internal components, leading to its death.
- Cytotoxic T cells trigger apoptosis by activating pro-apoptotic genes in the infected or cancerous cell.
- The activation of these genes leads to the production of proteins like "Bax" that cause the release of cytochrome C from the mitochondria.
- The release of cytochrome C activates caspases, which cause the proteolytic destruction of cell components, leading to cell death.
Natural Killer Cells: A Brief Overview
- Natural killer (NK) cells are part of the innate immune system, not the adaptive immune system.
- NK cells are similar in function to cytotoxic T cells in that they kill infected or cancerous cells through the release of perforin and granzymes.
- However, NK cells do not need to recognize specific antigens on MHC class I.
- Therefore, NK cells can kill cells that lack normal MHC Class I expression or cells that express "stressed" versions of MHC I called "MICA" (MHC Class I related chain A).
- NK cells can also be activated by the presence of IgG antibodies.
Summary of Adaptive Immunity
- Adaptive immunity is comprised of humoral immunity and cell-mediated immunity.
- Humoral immunity is triggered by exogenous antigens (outside of cells) and relies on B cells to produce antibodies.
- Cell-mediated immunity targets intracellular antigens (inside of cells) and relies on cytotoxic T cells to kill infected or cancerous cells.
- Natural killer cells are part of the innate immune system, not the adaptive immune system, even though they use similar mechanisms to kill cells as cytotoxic T cells.
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Explore the key components and functions of the adaptive immune system in this quiz. Learn about lymphoid tissues, circulating effector proteins, and inflammatory cytokines that play vital roles in immune responses. Test your knowledge on how these elements work together to defend the body.
