chapter 43: the immune system
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Chapter 43: The Immune System. Essential Knowledge. 2.d.2 - Homeostatic mechanisms reflect both common ancestry and divergence due to adaptation to different environments (43.3). 2.d.3 – Biological systems are affected by disruptions to their dynamic homeostasis (43.2-43.4). - PowerPoint PPT PresentationTRANSCRIPT
Chapter 43: The
Immune System
Essential Knowledge2.d.2 - Homeostatic mechanisms reflect both
common ancestry and divergence due to adaptation to different environments (43.3).
2.d.3 – Biological systems are affected by disruptions to their dynamic homeostasis (43.2-43.4).
2.d.4 – Plants and animals have a variety of chemical defenses against infections that affect dynamic homeostasis (43.1-43.4).
3.d.2 Cells communicate with each other through direct contact with other cells or from a distance via chemical signaling (43.2).
Focus TopicsImmunological responses to pathogens, toxins,
and allergensVertebrate immune systems have nonspecific
and nonheritable defense mechanisms against pathogens
The mammalian immune system includes two types of specific responses: cell mediated and humoral
In the cell-mediated response, cytotoxic T cells, a type of lymphocytic white blood cell, “target” intracellular pathogens when antigens are displayed on the outside of the cells.
Focus TopicsIn the humoral response, B cells, a type
of lymphocytic white blood cell, produce antibodies against specific antigens.
Antigens are recognized by antibodies to the antigen.
Antibodies are proteins produced by B cells, and each antibody is specific to a particular antigen.
A second exposure to an antigen results in a more rapid and enhanced immune response.
Introduction to ImmunityDefense systemProtects from bacteria, viruses, other
pathogens, early-stage cancer cellsThree types of immunity:
1. Innate: nonspecific defense mechanisms external physical barriers of skin mucous membranes
internal defenses of chemicals and phagocytic cells
Ex: gastric juices, histamines, inflammatory response
Introduction to ImmunityThree types of immunity:
2. Acquired: adaptive immunity, line of defense in which lymphocytes react specifically to threat, two types Humoral – antibodies produced by cells
mark microbes for destruction, involves B cells
Cell-mediated – cytotoxic lymphocytes destroy infected body cells, cancer cells and foreign tissue, involves helper T cells
3. Passive: acquired temporarily◦ Ex: through breast-feeding
Organs/Tissues/Glands involved:◦ Bone/bone marrow◦ Spleen◦ Stomach/Intestines◦ Skin◦ Lungs◦ Lymph nodes
Introduction to ImmunityLeukocytes are the cells which are
the bulk of your immune system.◦Produced or stored in:
Thymus, spleen, and bone marrow (called the lymphoid organs)
There are also clumps of lymphoid tissue throughout the body (primarily as lymph nodes) that hold leukocytes
Introduction to ImmunityThe two basic types of
leukocytes are:◦Phagocytes, cells that chew up
invading organisms Ex: neutrophils
◦Lymphocytes, cells that allow the body to remember and recognize previous invaders and help the body destroy them Ex: B and T cells
The leukocytes circulate through the body between the organs and nodes via lymphatic vessels and blood vessels.
In this way, the immune system works in a coordinated manner to monitor the body for germs or substances that might cause problems.
Introduction to Immunity
Innate ImmunityExternal defenses
◦Skin – secretions lower pH (discourage microbial attack)
◦Mucous membranes (line digestive, respiratory, genitourinary tracts) Gastric juice – lowers pH to acidic Epilethial lining of respiratory – traps microbes
◦Lysozyme – enzyme that attacks bacterial cell walls Present in tears, saliva, and mucus
◦Serve as physical barriers to microbes
Innate ImmunityInternal defenses
◦Systemic response may include: Increase in number of circulating WBCs Fever
Triggered by toxins produced by pathogen or chemicals released by immune system
Stimulates phagocytosis and thus tissue repair and immune response
Inflammation Redness, swelling, heat Occurs when damaged mast cells (in connective
tissue) release histamine Histamine: triggers dilation and leakiness of
blood vessels
Innate ImmunityInternal defenses
◦Relies upon phagocytosis by special WBCs (phagocytes) These cells release antimicrobial proteins to
help initiate an inflammation response Rely upon cell surface rectors to bind to microbial
surface receptors Then, engulfs microbe and kill them using lysosome
toxins Neutrophils: most numerous phagocytic
WBCs Eosinophils: WBCs that attack multicellular
parasites Dendritic cells: stimulate acquired immunity
Innate ImmunityInternal defenses
◦Natural killer (NK) cells: nonphagocytic cells that also participate in innate defenses Recognize general features of viral-infected or
cancer cells Attaches to them and triggers apoptosis
◦Complement system: 30 proteins that can lyse microbes, trigger inflammation or assist in acquired immunity
◦Interferons: stimulate neighboring cell to produce anti-viral reproduction substances
Acquired ImmunityIntroduction
◦First visit: Immune System Preview◦Key cells: lymphocytes (WBCs)◦Activated by contact with microbes OR
by cytokines (proteins secreted by macrophages)
◦Recognizes antigens (foreign molecules) Most are large proteins or polysaccharides Often protrude from surface of microbe Epitope: region of antigen to which
lymphocyte attaches
Acquired ImmunityAntigen Recognition
◦Performed by B and T cells B lymphocytes (B cells) and T
lymphocytes (T cells) circulate in blood and lymph
Found in spleen and lymph nodes Recognized by antibodies to the
particular antigen Both contain membrane-bound antigen
receptors which allows them to recognize specific epitopes (where they will bind)
Acquired ImmunityAntigen Recognition
◦B cell receptor Y-shaped Consists of 4 polypeptide chains (two
light chains and two heavy chains)◦T cell receptor
One alpha chain and one beta chain Recognize special cell-surface proteins
made by MHC (major histocompatibility complex – a family of genes)
Acquired ImmunityPrimary immune response
◦Begins this response upon first exposure to an antigen (foreign molecule)
◦Requires about 10-17 days to yield maximum response via T and B-cells
◦ Immunological memory: secondary immune response that provides long-term protection against a previously encountered pathogen “To avoid illness, expose yourself to germs,
enabling your immune system to develop antibodies. I don’t know why everyone doesn’t do this. Maybe they have something against living forever.” ~Dwight Schrute
Acquired ImmunityTwo types:
◦Humoral immune response Involves B cell activation and production of
antibodies Antibodies then circulate in blood and lymph Provide defense against pathogens and toxins
in the extracellular fluid◦Cell-mediated response
Involves cytotoxic T cells that destroy infected body cells, cancer cells and transplanted tissues
Relies upon Helper T cells to activate B cells and cytotoxic T cells
Acquired ImmunityOnly found in vertebratesT cells and B cells
◦Types of WBCs called lymphocytes◦Originate from stem cells in the bone marrow◦Some lymphocytes migrate from the marrow
to the thymus These mature into T cells
◦Some lymphocytes remain in the marrow These develop into B cells
◦Other lymphocytes stay in the blood and become the natural killer cells of innate immunity
Acquired ImmunityAntigens are substances that prompt a
response from a B or T cellAntigen receptor proteins allow B and T
cells to bind to antigens◦Specific enough to bind to just one part of
one molecule from a particular pathogen◦Millions of antigen receptors (AR) are
produced, but all AR’s are identical on each B and T cell
◦Up to 100,000 AR’s on the surface of each B and T cell!
◦See Fig. 43.9, page 935
Antigen SpecificsUsually foreignLarge molecules
◦Proteins or polysaccharidesProtrude from the surface of foreign cells or
virusesSome, such as bacterial toxins, are released
into the extracellular fluidSmall, accessible portion that binds to an AR
is called an epitope or antigenic determinant◦Each antigen has several different epitopes, each
binding a receptor with a different specificity
B Cell and Antibody-Antigen RecognitionEach B cell AR is a Y-shaped molecule
of 4 polypeptide chains◦Two identical heavy chains◦Two identical light chains◦Fig. 43.9, page 935
Light and heavy chains have a constant region where amino acid sequences don’t vary much and a variable region on which the amino acid sequence varies extensively from one B cell to another
Formation of AntibodiesWhen a B cell AR binds to an antigen, that will elicit
B cell activation eventually leading to the formation of cells that secrete a soluble form of the receptor◦ The secreted protein is an antibody or immunoglobulin
(Ig)Antibodies are Y-shaped like the B cell AR’s
◦ But are secreted rather than membrane-bound◦ Antibodies are the proteins that defend against
pathogens◦ Differences in amino acid sequences of variable regions
on the B cell AR’s allow highly specific bindingB cell AR’s and antibodies bind to intact antigens in
the blood and lymphFig. 43.10, page 936
T Cell Antigen RecognitionT cell AR’s are two different polypeptide
chains, an α chain and a β chain, linked by a disulfide bridge (fig. 43.11, page 936)
Outer tips of each chain consist of the variable region and are where the antigen binds
Remainder of the molecule is the constant region
Bind to fragments of antigens that are presented on the surface of host cells◦ The host protein that displays the antigen fragment
on the cell surface is the MHC (major histocompatibility complex) molecule
Recognition of Protein Antigens by T CellsBegins when a pathogen or part of a pathogen either
infects of is taken in by a host cell (Fig. 43.12, page 937)
Enzymes in the host cell break the antigen into smaller peptides called antigen fragments◦ These bind to MHC molecules inside the cell◦ MHC molecule with the bound antigen fragment move to
the cell surface resulting in antigen presentation This advertises that the host cell contains a foreign substance
If the cell displaying an antigen fragment encounters a T cell that is the right match, the AR on the T cell will bind to the antigen fragment and the MHC molecule◦ This binding is necessary for a T cell to participate in an
adaptive immune response
Acquired ImmunityActive immunity: acquired when
body produces antibodies and develops immunological memory from either exposure to actual pathogen OR from immunization/vaccinization◦Vaccine can be:
1) inactive toxic 2) killed/weakened microbe 3) portion of microbe 3) genes for microbial proteins
Passive ImmunityPassive immunity: temporary
immunity provided by antibodies◦Supplied through:
Placenta to fetus Milk to nursing infant Antibody injection
Tissue TransplantLimited by immune system’s ability to
distinguish self from nonselfImmune system responds negatively
to chemical markers (unlike itself) during blood transfusions (and tissue transplantation)
Mother and fetus: Rh factor◦Rh: protein, RBCs antigen◦If fetal blood is different from mother, fetal
blood can leak across placenta (creating immunological response from mother)
Tissue TransplantationOrgan and Tissue Transplants
◦May be rejected b/c the foreign MHC molecules are antigenic
◦Triggers immune response◦Use closely related donors and
immune system suppressor drugs to minimize risk of rejection
Immune System DiseasesAllergies
◦Hypersensitivity to certain environmental antigens (allergens)
◦Releases histamines – creating inflammatory response that may include: Sneezing Runny nose Difficulty breathing
◦Antihistamine drugs – those that combat these symptoms by blocking histamine receptors
◦Ex: Asthma, eczema (dry skin), environmental allergies (dust, dust mites, grass)
Immune System DiseasesAutoimmune Disease
◦Ex: Lupus, rheumatoid arthritis, insulin-dependent diabetes mellitus, multiple sclerosis
◦May be caused by failure in regulation of self-reactive lymphocytes
◦Causes immune system to turn against itself◦Ex: Scleroderma, a chronic autoimmune
disease that can lead to inflammation and damage of the skin, joints, and internal organs
◦Ex: Ankylosing spondylitis, a disease that involves inflammation of the spine and joints, causing stiffness and pain
Immune System DiseasesImmunodeficiency diseases
◦Ex: AIDS (caused by HIV), cancer, Hodgkin’s disease, stress
◦Suppress the immune system◦Become highly susceptible to opportunitistic
infections (like pneumonia, flu, etc)◦Ex: DiGeorge syndrome (thymic
dysplasia), a birth defect in which kids are born without a thymus gland
◦Ex: Chediak-Higashi syndrome and chronic granulomatous disease both involve the inability of the neutrophils to function normally
Exclusion StatementsMemorization of the structures of
specific antibodies is beyond the scope of the course and the AP Exam.