BIOL 318: CH. 21 - IMMUNE SYSTEM: ADAPTIVE IMMUNITY
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175 Terms
What line of defense is adaptive immunity?
Third line of defense with specificity and memory.
What are the two main forms of adaptive immunity?
Cell-mediated (cellular) and antibody-mediated (humoral) immunity.
What type of pathogens does cell-mediated immunity target?
Intracellular pathogens like viruses, certain bacteria, yeasts, protozoans, parasitic worms, cancer cells, and transplanted cells.
Why can't antibodies handle intracellular pathogens?
Because the pathogens, like viruses, are inside the host cells.
How do lymphocytes function in cell-mediated immunity?
They directly attack infected or abnormal cells.
What else does cell-mediated immunity act against besides pathogens?
Parasitic worms, cancer cells, and transplanted tissue or organ cells.
What type of pathogens does antibody-mediated immunity target?
Extracellular pathogens like bacteria, viruses, yeasts, protozoans, toxins, venoms, and allergens.
How does antibody-mediated immunity handle foreign erythrocytes in a mismatched transfusion?
It destroys them as part of the immune response.
How do antibodies affect pathogens in humoral immunity?
They tag pathogens for destruction but do not directly destroy them.
Why might both humoral and cellular immunity be used against the same pathogen?
Because they may attack it in different ways or at different stages of its life cycle.
What is active immunity?
Body produces antibodies or T cells against a pathogen.
What is natural active immunity?
Production of own antibodies due to natural exposure to a pathogen.
What is an example of natural active immunity?
Eating something with a pathogen in it.
What is artificial active immunity?
Production of antibodies from vaccination.
What types of vaccines provide artificial active immunity?
Dead, attenuated (weakened), or fragments of pathogens.
Why are booster shots given?
To restimulate immune memory and maintain a high level of protection (e.g., tetanus boosters).
What is passive immunity?
Receiving antibodies or serum from another person or animal already immune to the pathogen.
How long does passive immunity typically last?
Only 2 or 3 weeks, until the acquired antibodies are degraded.
What is natural passive immunity?
Temporary immunity from antibodies received from another person naturally.
How does a fetus acquire natural passive immunity?
Through antibodies passed from the mother via the placenta.
How does a baby acquire natural passive immunity after birth?
Through antibodies in breast milk.
What is artificial passive immunity?
Temporary immunity from an injection of immune serum containing antibodies.
What are examples of situations treated with artificial passive immunity?
Snakebites, botulism, tetanus, rabies.
What is an antigen?
Any molecule that can bind an antibody.
What are examples of free antigens?
Venoms, toxins, food-borne substances.
What are examples of antigen components in organisms?
Plasma membranes and bacterial cell walls.
What is the role of an antigen in the immune system?
Triggers an immune response.
What size and complexity do typical antigens have?
Larger molecules with more complexity.
How does molecular uniqueness affect immune response?
More uniqueness leads to fewer self-attacks.
What types of molecules can act as antigens?
Proteins, polysaccharides, glycolipids.
Where are antigens typically located?
Facing the extracellular fluid (ECF).
What is agglutination?
Collection of red blood cells by antibodies.
What part of an antigen stimulates immune responses?
Epitopes (antigenic determinants).
What is a hapten?
A molecule too small to be antigenic on its own; considered an incomplete antigen.
How can a hapten become antigenic?
By binding to a larger host molecule to form a complex that can bind to antibodies and stimulate an immune response.
What are examples of common haptens?
Poison ivy, cat dander, penicillin.
What is the most common drug allergy?
Penicillin allergy.
How does penicillin cause an allergic reaction?
It binds to host proteins, forming a complex that activates mast cells and triggers the release of histamine and other inflammatory chemicals.
What can a severe penicillin allergy lead to?
Anaphylactic shock, which can cause death.
What are antibodies also known as?
Immunoglobulins (Igs).
What type of globulins are antibodies and where are they produced?
Gamma globulins produced by plasma cells in the bloodstream.
How many polypeptide chains make up an antibody?
Four polypeptides.
What are the types of polypeptide chains in an antibody?
Two light chains (small) and two heavy chains (bent, give T or Y shape).
What holds the polypeptide chains of an antibody together?
Disulfide bonds.
What region is present in all antibody chains and what does it form?
Variable regions that form two antigen-binding sites.
How many unique antibodies exist in the human body?
Approximately 10 billion to 1 trillion.
What process creates diversity in antibodies through recombining DNA?
Somatic recombination.
What is somatic recombination?
Mixing of nucleotide sequences to form new DNA combinations in somatic cells.
What other process increases antibody diversity besides recombination?
High genetic mutation rate (somatic hypermutation).
What is somatic hypermutation?
Creation of new DNA sequences through mutation, not just recombination.
How many classes of antibodies are there?
Five classes.
What are the five classes of antibodies?
IgA, IgD, IgE, IgG, IgM.
Which antibody is important for newborn immunity and why?
IgG because it crosses the placenta easily.
Which antibody is passed to infants through breast milk and colostrum?
IgA.
How do antibody classes differ?
In location, structure, timing, and function.
Where are antibodies found besides blood plasma?
Lymph, mucus, saliva, intestinal secretions, tears, and breast milk.
Which immune cells have antibodies as integral membrane proteins?
Basophils, mast cells (innate immunity) and B lymphocytes (adaptive immunity).
Where are T lymphocytes born?
Red bone marrow from hemopoietic stem cells.
Where do T lymphocytes travel for training?
Thymus.
Where in the thymus do T cells undergo their first test?
Cortex.
What structure protects developing T cells in the cortex?
Blood-thymus barrier.
Who gives the first test in the cortex and what kind of selection is it?
Epithelial cells; positive selection.
What does the first test check for?
Capacity of T cells to respond to fragments of pathogens.
What happens if a T cell has proper receptors during the first test?
Receives a life-sparing signal and becomes immunocompetent.
What happens if a T cell lacks receptors during the first test?
Receives no signal and can retake the test.
How can a T cell retake the first test?
Reshuffles its DNA for new receptors.
What happens if the T cell fails again after retaking the test?
Dies by apoptosis and is phagocytized by cortical macrophages.
Where do T cells go after passing the cortex test?
Medulla.
Who gives the second test in the medulla and what kind of selection is it?
Macrophages and reticular cells; negative selection.
What are T cells presented with in the medulla during the second test?
Self-antigens and binding proteins (MHC).
What happens if a T cell responds to self-antigens?
Destroyed by macrophages.
What does the second test ensure?
Self-tolerance so that T cells won’t attack the body’s own tissues.
What percentage of T cells survive both tests?
2%.
What is the result of passing both tests in the thymus?
Becomes part of the naïve lymphocyte pool.
What does it mean to be a naïve T cell?
Has not yet encountered a foreign antigen.
Where do naïve T cells go after leaving the thymus?
Travel by blood and lymph to lymphatic tissues and organs like the spleen.
What do naïve T cells do once deployed?
Await activation by encountering their specific antigen.
What do T cells require to recognize an antigen?
APCs (antigen-presenting cells).
What are the types of antigen-presenting cells (APCs)?
Dendritic cells, macrophages, B cells.
What do APCs depend on to present antigens?
MHC genes (proteins).
What is the role of MHC I complexes in antigen presentation?
All cells can present antigens on MHC I complexes, serve as ID tags.
How are antigens processed by APCs?
Ingested by endocytosis, broken into fragments, epitopes bound to MHC proteins.
How do T cells interact with APCs?
Monitor APCs, test for antigen.
What happens if an APC displays a self-antigen?
T cells disregard it.
What happens if an APC displays a nonself-antigen?
Immune response against the foreign antigen.
What is the primary function of T cells?
Directly attack infected/foreign cells and form memory.
What do cytotoxic T cells (TC) do?
Carry out the attack on foreign cells.
What is the role of helper T cells (TH)?
Promote the activity of TC cells and also contribute to humoral immunity.
What is the function of regulatory T cells?
Inhibit multiplication and cytokine amplification by other T cells, reducing the response after attack.
Why is the regulatory T cell function important?
Without it, TC cells would continue producing inflammatory cytokines, potentially causing long-term tissue damage.
It also reduces the risk of autoimmune diseases.
What are memory T cells (TM) and how do they arise?
Memory T cells arise from TC cells and remain long-term after an infection.
What are the three stages of both cellular and humoral immunity?
Recognition, attack, and memory.
What do APCs do after migrating to lymph nodes?
What do APCs do after migrating to lymph nodes?
Present antigens to TC and TH cells.
What proteins do TC cells respond to?
MHC-I proteins.
Where are MHC-I proteins found?
All nucleated cells.
What do MHC-I proteins present?
Internal peptides from within the cell.
What happens if MHC-I peptides are normal self-antigens?
No T-cell response.
What happens if MHC-I peptides are viral or abnormal antigens?
T-cell response → cell destruction.
What proteins do TH cells respond to?
MHC-II proteins.
What do MHC-II proteins present?
External antigens, phagocytosed foreign material.