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Questions and Answers
What are the two main types of immunity?
What are the two main types of immunity?
Innate and Adaptive
What is the primary function of an antigen?
What is the primary function of an antigen?
To stimulate an immune response
What is an epitope?
What is an epitope?
A small region of an antigen that is recognized by the immune system. It is the portion of a molecule that will combine with a particular antibody combining site.
What is a hapten?
What is a hapten?
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What are superantigens?
What are superantigens?
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What are heterophile antigens?
What are heterophile antigens?
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Which of the following is not a primary lymphoid organ?
Which of the following is not a primary lymphoid organ?
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What is the main function of the spleen?
What is the main function of the spleen?
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What are the two main types of adaptive immunity?
What are the two main types of adaptive immunity?
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What are T cell receptors (TCRs)?
What are T cell receptors (TCRs)?
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What is the main function of B cells?
What is the main function of B cells?
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Which type of cell acts as an antigen-presenting cell?
Which type of cell acts as an antigen-presenting cell?
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The thymus is a primary lymphoid organ.
The thymus is a primary lymphoid organ.
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Where are secondary lymphoid organs located?
Where are secondary lymphoid organs located?
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The lymph nodes are the only secondary lymphoid organs.
The lymph nodes are the only secondary lymphoid organs.
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What is the role of the lymph nodes in the immune system?
What is the role of the lymph nodes in the immune system?
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The spleen is only involved in the adaptive immune response.
The spleen is only involved in the adaptive immune response.
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The thymus is the only primary lymphoid organ.
The thymus is the only primary lymphoid organ.
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What is the role of the bone marrow in the immune system?
What is the role of the bone marrow in the immune system?
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Which of the following are examples of mucosal-associated lymphoid tissues (MALT)?
Which of the following are examples of mucosal-associated lymphoid tissues (MALT)?
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What is the role of the mucosal and cutaneous lymphoid tissues in the immune system?
What is the role of the mucosal and cutaneous lymphoid tissues in the immune system?
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The immune system can only recognize a limited number of antigens.
The immune system can only recognize a limited number of antigens.
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The adaptive immune system is a more specific defense system than the innate immune system.
The adaptive immune system is a more specific defense system than the innate immune system.
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The innate immune system is the first line of defense against infection.
The innate immune system is the first line of defense against infection.
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What is the role of cytokines in the immune system?
What is the role of cytokines in the immune system?
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The adaptive immune system is also responsible for recognizing and destroying cancer cells.
The adaptive immune system is also responsible for recognizing and destroying cancer cells.
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Study Notes
Basics of Immunity
- Immunity is a complex biological system that protects the body from pathogens and foreign substances.
- Two main types of immunity exist: innate and adaptive.
- Innate immunity provides immediate, non-specific defense mechanisms.
- Adaptive immunity develops more slowly but is highly specific to the invading pathogen.
Terminology
- Antigen: A molecule or substance recognized by the adaptive immune system's receptors. It triggers an immune response. Antigens are composed of epitopes, which are specific sites for antibodies to bind to and immunogens. Examples include toxins, microorganisms (bacteria, viruses), and self/foreign antigens.
- Immunogen: A substance that induces an immune response. Often an antigen is also an immunogen, but not always. An example of an immunogen is the hepatitis B virus surface antigen.
- Hapten: An incomplete antigen that cannot induce a response alone but can stimulate an immune response when attached to a carrier molecule. Penicillin is an example.
- Epitope: A specific antigenic determinant recognized by the immune system. It's a part of a larger antigen that antibodies or T-cell receptors can bind to.
- Adjuvant: A substance that enhances the immune response to an antigen.
- Superantigen: An antigen that activates a large percentage of T cells, often leading to excessive cytokine production. Examples are Staphylococcal enterotoxins (food poisoning).
- Heterophile antigen: Common antigens that exist among humans, animals and microorganisms. Similarities in antigenic structures with tissues or extracellular components can trigger cross-reactive antibodies and lead to autoimmune diseases.
Epitopes
- Immune cells recognize discrete sites on macromolecules, called epitopes.
- Epitopes are immunologically active parts of an immunogen, linking with antibodies (or other receptors).
- An epitope is part of a larger antigen (e.g., a viral protein) that a specific antibody can bind to. A single viral protein may contain many epitopes capable of binding various antibodies & T-cell receptors.
Haptens
- Haptens are incomplete antigens; they don't induce immune responses by themselves but can do so when coupled to a carrier molecule.
- They can react with specific immune products.
- Penicillin is a typical example.
Superantigens
- Superantigens are antigens that polyclonally activate a significant portion of T cells.
- They can lead to overproduction of cytokines, which can be harmful.
- Staphylococcal enterotoxins are examples.
Heterophile Antigens
- Heterophile antigens are antigens present in various organisms and can induce cross-reactive antibodies.
- The immune response to these can result in autoimmune diseases (responses directed against self).
Components of the Immune System
- These include primary and secondary lymphoid organs and their associated cells.
- The primary lymphoid organs include the bone marrow and thymus.
- The secondary lymphoid organs include lymph nodes, spleen, and mucosa-associated lymphoid tissue (MALT).
Mechanisms of Immunity
- Innate immunity acts as the immediate and first line of defense, reacting quickly to any foreign invader.
- Adaptive (acquired) immunity is slower, developing after exposure to an invader.
Components of the Innate Immune Response
- Cells like epithelial barriers, phagocytic cells (neutrophils & macrophages), dendritic cells, natural killer cells, and innate lymphoid cells are involved.
- Proteins of the complement systems act against pathogens.
- Neutrophils are the first cells to arrive at infection and injury sites, phagocytosing bacteria.
- Macrophages are resident cells in various tissues, phagocytosing antigens and pathogens, secreting cytokines.
- Natural killer (NK) cells provide early protection against viruses and intracellular bacteria by recognizing mutated or damaged cells.
- Dendritic cells are antigen presenting, capturing and processing antigens to stimulate T cells.
Cellular Receptors for Microbes & Foreign Substances
- Cells in innate immunity have receptors for microbes and damaged-cell products.
- These receptors recognize shared patterns among pathogens (pathogen-associated molecular patterns).
- These patterns are crucial for the cell's ability to recognize intruders.
- Receptors are located in multiple cellular compartments (plasma membrane, endosomal, cytosol).
Five Major Families of Cellular Receptors in Innate Immunity
- TLRs (Toll-like receptors)
- CLRs (C-type lectin receptors)
- NLRS (NOD-like receptors)
- RLRS (RIG-like receptors)
- CDSS (cytosolic DNA sensors)
Adaptive Immunity
- Humoral immunity protects against extracellular microbes and toxins. Mediated by B lymphocytes and antibodies.
- Cellular immunity is involved in responding to intracellular microbes and cancers. Mediated by T lymphocytes.
- Lymphocytes have highly specific receptors for various substances called antigens.
Cells of Adaptive Immunity-T lymphocyte
- Naïve T lymphocytes recognize antigens via specific T cell receptors (TCRs).
- Activated T lymphocytes differentiate into effector T (helper, cytotoxic, or regulatory) cells to eliminate pathogens.
- Helper T lymphocytes activate B cells & other leukocytes.
- Cytotoxic T lymphocytes kill infected cells.
- Regulatory T cells regulate the immune response.
B Lymphocytes
- B lymphocytes are crucial in producing antibodies.
- Differentiate into plasma cells that produce antibodies to counteract antigens.
- Activated B cells can also form memory cells to provide long-term immunity.
Antigen-Presenting Cells
- Dendritic cells are major antigen-presenting cells initiating T cell responses to protein antigens.
- Macrophages function as antigen-presenting cells by activating T cells; they phagocytose microbes and protein antigens processing, and present them as peptide fragments to T cells.
- Macrophages are essential effector cells in cell-mediated immunity.
Tissues of the Immune System
- The immune system is not confined to tissues in one area; it comprises primary and secondary lymphatic organs.
- Primary lymphatic organs: Bone marrow & thymus; where lymphocytes develop/mature.
- Secondary lymphatic organs: Lymph nodes, spleen & mucosa-associated lymphoid tissue (MALT); where immune responses are initiated.
Lymphoid organs
- Lymphoid organs, either central or primary (containing precursor lymphoid cells — bone marrow and thymus) or peripheral or secondary (encountering antigens and developing different immune responses — lymph nodes, spleen, and mucosa-associated lymphoid tissue (MALT).
- The lymph nodes & spleen contain antigen-presenting cells and lymphocytes.
- Antigens are transported to these organs and stimulate immune responses.
Thymus
- The thymus is a primary lymphoid organ where maturation and selection of T cells takes place.
- T cell precursors migrate from bone marrow for maturation into mature, naïve T cells.
Homes of Acquired Immunity
- Primary lymphoid organs are where T and B cells become immunologically competent.
- Secondary lymphoid organs is where they await pathogens.
- This includes lymph nodes, spleen, tonsils, MALT (mucosa-associated lymphoid tissue e.g. Peyer's patches/Gut-associated lymphoid tissue).
Origin of Immune Cells
- All immune cells originate from hematopoietic stem cells in bone marrow.
- These cells differentiate into various types of immune cells (innate and adaptive).
Secondary Lymphoid organs
- Lymph nodes are aggregates of tissues positioned strategically throughout lymphatic channels to encounter and process antigens.
- Antigen-presenting cells (like dendritic cells [DCs]) transport antigens from tissues into lymph nodes to encounter lymphocytes.
Spleen
- The spleen is an abdominal organ involved in immune responses to blood-borne antigens.
- It filters circulating blood, removing pathogens and damaged cells.
- It also produces antibodies and contains various immune cells, including macrophages and DCs, to initiate adaptive immune responses.
The cutaneous and mucosal Lymphoid systems
- These systems are located under the epithelia, responding to pathogens entering skin and mucosal sites.
- The anatomical regions such as tonsils & Peyer patches are part of the mucosal lymphoid tissue.
Lymphatic System (Diagram)
- Lymphocytes continually recirculate between blood and lymphoid organs.
- This allows immune cells to survey and respond to antigens in different tissues.
Normal lymph node, microscopic/microscopic magnification
- The lymph node has a capsule and well-defined zones with various cell types.
- The germinal centers are where B cell activation and antibody production occur. Macrophages and dendritic cells are involved and display antigens.
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Description
Test your knowledge on the fundamentals of immunity, including innate and adaptive systems. Explore key terminologies related to antigens, immunogens, and more. This quiz will help you understand how the immune system protects the body from pathogens.
