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What are epitopes also known as?
antigenic determinants
Which cells give rise to plasma cells that secrete antibodies?
The first exposure to a specific antigen represents the secondary immune response.
False
Match the immune response with its description:
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What are the two major kinds of defense that have evolved in the immune system?
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Viruses are considered alive based on the characteristics of living organisms.
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______ deal with abnormal body cells that may develop into cancers.
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What are the two types of immunity present in animals' immune systems?
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What is the first barrier to pathogens in insects?
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Which class of immunoglobulin is the most abundant in blood?
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IgG is the only immunoglobulin class that crosses the placenta to confer passive immunity on the fetus.
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Passive immunity can be conferred naturally when IgA passes from mother to infant in ___________ milk.
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What class of immunoglobulin triggers the release of histamine and other chemicals that cause allergic reactions?
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What type of response is characterized by the secretion of antibodies by B cells?
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What is the role of Helper T cells in the immune response?
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Cytotoxic T cells are responsible for defending against extracellular pathogens. (True/False)
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The killing action of cytotoxic T cells involves the secretion of _______ and Granzymes.
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What is the term used to describe the inactive state in which some viruses may remain in a host?
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How does HIV elude the immune system?
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Loss of helper T cells impairs both the humoral and cell-mediated immune responses and leads to AIDS.
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True or False: Herpes simplex viruses can be present in a human host without causing symptoms.
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Study Notes
Immune System
- The immune system is crucial for defending against external and internal threats, such as viruses, bacteria, protists, and fungi.
- Animals must defend themselves against these pathogens, which can be recognized as "not self" by the immune system.
- The immune system responds by producing immune cells and proteins.
Innate Immunity
- Innate immunity is present from birth and provides immediate, non-specific defense against pathogens.
- It consists of external barriers (skin, mucous membranes, and secretions) and internal cellular and chemical defenses (phagocytic cells, antimicrobial proteins, and inflammatory responses).
- In invertebrates, innate immunity includes an exoskeleton, digestive system defenses, and hemocytes that perform phagocytosis.
Barrier Defenses
- Barrier defenses include the skin and mucous membranes of the respiratory, urinary, and reproductive tracts.
- Mucus traps and removes microbes, while many body fluids, such as saliva and tears, are hostile to microbes.
- The low pH of the skin and digestive system prevents microbial growth.
Non-Specific Patrol (Internal Barrier)
- Phagocytic cells, such as neutrophils and macrophages, engulf and digest foreign substances and microbes.
- Anti-microbial proteins, such as interferon, provide innate defense against viruses and help activate macrophages.
- The complement system, consisting of about 30 proteins, causes lysis of invading cells and helps trigger inflammation.
Inflammatory Response
- The inflammatory response is a localized response to tissue damage, triggered by the release of histamine and prostaglandins.
- It increases local blood supply, delivers WBCs, RBCs, platelets, and clotting factors, and leads to swelling, redness, heat, and pus formation.
- Inflammation can be either local or systemic, and fever is a systemic inflammatory response.
Acquired Immunity
- Acquired immunity, also known as adaptive immunity, develops after exposure to pathogens and provides specific defense against them.
- Lymphocytes, such as B cells and T cells, recognize and respond to antigens through receptor proteins.
- Lymphocytes contribute to immunological memory, an enhanced response to a foreign molecule encountered previously.
Antigen Receptors
- B cells and T cells have receptor proteins that can bind to foreign molecules, with each lymphocyte recognizing a specific epitope on an antigen.
- B cells give rise to plasma cells, which secrete proteins called antibodies or immunoglobulins.
- T cells can bind to an antigen that is free or on the surface of a pathogen, and bind to antigen fragments presented on a host cell.
The Role of MHC
- MHC molecules bind and transport antigen fragments to the cell surface, allowing T cells to detect the antigen.
- Class I MHC molecules are found on almost all nucleated cells and display peptide antigens to cytotoxic T cells.
- Class II MHC molecules are found on specialized cells, such as macrophages, B cells, and activated T cells, and display antigens to helper T cells.
Clonal Selection
- The binding of a mature lymphocyte to an antigen induces the lymphocyte to divide rapidly, producing a clone of cells.
- Clonal selection produces two types of clones: short-lived activated effector cells and long-lived memory cells.### Immune Response
- The primary immune response occurs when the body first encounters an antigen, and it involves the generation of effector B cells (plasma cells) and the activation of T cells to their effector forms.
- The secondary immune response is more efficient and occurs when the body encounters an antigen it has previously seen, and it involves the activation of memory cells.
Acquired Immunity
- Acquired immunity defends against infection of body cells and fluids and has two branches: humoral immune response and cell-mediated immune response.
- Humoral immune response involves the activation and clonal selection of B cells, resulting in the production of secreted antibodies.
- Cell-mediated immune response involves the activation and clonal selection of cytotoxic T cells, which defend against intracellular pathogens and cancer.
Humoral Immune Response
- The humoral immune response is characterized by the secretion of antibodies by B cells.
- Antibodies defend against extracellular pathogens by binding to antigens, thereby neutralizing pathogens or making them better targets for phagocytes and complement proteins.
- B cells are activated by antigen binding to helper T cells, which secrete cytokines that stimulate B cells.
Cell-Mediated Immune Response
- The cell-mediated immune response involves the activation of cytotoxic T cells, which defend against intracellular pathogens and cancer.
- Cytotoxic T cells recognize and bind to infected cells or cancer cells, and then secrete proteins that destroy the target cells.
Helper T Cells
- Helper T cells respond to nearly all antigens and play a central role in both humoral and cell-mediated immune responses.
- Helper T cells bind to antigen-presenting cells and secrete cytokines that stimulate other lymphocytes.
Cytotoxic T Cells
- Cytotoxic T cells are the effector cells in cell-mediated immune responses.
- Cytotoxic T cells recognize and bind to infected cells or cancer cells, and then secrete proteins that destroy the target cells.
Antibody Classes
- There are five major classes of antibodies, or immunoglobulins, which differ in distribution and function.
- The five classes are IgM, IgG, IgA, IgE, and IgD, each with distinct characteristics and functions.
Active Immunization
- Active immunity develops naturally in response to an infection or following immunization (vaccination).
- Immunization involves the introduction of a nonpathogenic form of a microbe or part of a microbe, which elicits an immune response and creates immunological memory.
Passive Immunity
- Passive immunity provides immediate, short-term protection and can be conferred naturally (e.g., through breast milk or placenta) or artificially (e.g., through injection of antibodies).
- Passive immunity can be used to protect against infection, but it does not create immunological memory.
Immune Rejection
- Immune rejection occurs when the body's immune system attacks transplanted tissues or organs due to differences in MHC molecules.
- Immunosuppressive drugs can facilitate transplantation, but lymphocytes in bone marrow transplants can cause the donor tissue to reject the recipient.
Blood Groups
- Antigens on red blood cells determine a person's blood type (A, B, AB, or O).
- Antibodies to nonself blood types exist in the body, and transfusion with incompatible blood can lead to destruction of the transfused cells.
Disruption in Immune System Function
- Disruption in immune system function can lead to disease or exacerbate existing conditions.
- Some pathogens have evolved to diminish the effectiveness of host immune responses.
Allergies
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Allergies are exaggerated responses to antigens called allergens.
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In localized allergies, IgE antibodies produced after first exposure to an allergen attach to receptors on mast cells, leading to the release of histamine and other mediators that cause typical allergy symptoms.### Autoimmune Diseases
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In autoimmune diseases, the immune system loses tolerance for self and attacks certain molecules of the body.
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Examples of autoimmune diseases include systemic lupus erythematosus, rheumatoid arthritis, insulin-dependent diabetes mellitus, and multiple sclerosis.
Exertion, Stress, and the Immune System
- Moderate exercise improves immune system function.
- Psychological stress disrupts hormonal, nervous, and immune systems.
Immunodeficiency Diseases
- Inborn immunodeficiency results from hereditary or developmental defects that prevent proper functioning of innate, humoral, and/or cell-mediated defenses.
- Acquired immunodeficiency results from exposure to chemical and biological agents.
- Acquired immunodeficiency syndrome (AIDS) is caused by a virus.
Acquired Immune System Evasion by Pathogens
- Pathogens have evolved mechanisms to attack immune responses.
- Through antigenic variation, some pathogens change epitope expression and prevent recognition.
- Human influenza virus mutates rapidly, requiring new flu vaccines to be made each year.
- Human viruses can exchange genes with viruses of domesticated animals, posing a danger to human immune systems.
Latency
- Some viruses remain in a host in an inactive state called latency.
- Herpes simplex viruses can be present in a human host without causing symptoms.
Attack on the Immune System: HIV
- Human immunodeficiency virus (HIV) infects helper T cells, impairing both humoral and cell-mediated immune responses.
- HIV leads to AIDS through the loss of helper T cells.
- HIV evades the immune system through antigenic variation and ability to remain latent while integrated into host DNA.
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Description
Learn about the importance of the immune system in defending against external attacks from viruses, bacteria, protists, and fungi.
