chapter 43: the body’s defenses how does your body protect you from invaders?
TRANSCRIPT
Key Concepts
3 Lines of Defense
Innate vs. Acquired immunityPhagocytes, Lymphocytes, Antibodies, etc…
Humoral vs. Cell-Mediated immunity
Distinguishing self from non-self
Tissue transplantation
Immune Diseases/Disorders
Using HIV to treat Cancer??
http://abcnews.go.com/WNT/video/doctors-hiv-treat-cancer-17929437
What do you think?
How does your body INITIALLY defend itself from invasion? (1st line – specific or non?)
What happens if the invader gets past the 1st line? (2nd line – specific or nonspecific?)
What about more serious infections? (3rd line)
1st line Defense!!Skin, mucus, cilia, saliva, acids, tears, oils, bacteria, coughing, sneezing, vomiting
Antimicrobial proteins & Lysozymes
Innate vs. Acquired ImmunityInnate Immunity:– Present before exposure; since birth– Includes natural bodily defenses, mother’s
milk, or casual exposure– Broad-range capabilities, non-specific– External defenses:
• skin, mucus membranes, tears
– Internal Phagocytic cells • A.K.A.: “macrophages”; engulf invaders
Innate vs. Acquired Immunity
Acquired Immunity:– Develops only after exposure– Highly microbe-specific… how? – Employ lymphocytes & antibodies
• Involves both Humoral & Cell-Mediated responses
Phagocytic White Blood Cells
Recognize & bind to carbohydrate markers on foreign cell membranes– Triggers receptor-mediated endocytosis– Engulf & digest pathogens via
Phagocytosis
Types of White Blood Cells
Eosinophils: 1.5% of WBCs; destroy large parasites extracellularly
Natural killer (NK) cells: trigger apoptosis in virus-infected cells & cancer cells
Neutrophils: 60-70% of WBCs; engulf and destroy microbes at infected tissue; short lived
Monocytes: 5% of WBCs; develop into….
Macrophages: “big eaters” enzymatically destroy microbes; can be found in spleen, lymph nodes, and other organs
Leukocyte vs. Lymphocyte
Leukocyte = – White blood cells (WBC’s)
Lymphocyte = – Specific type of WBC that mature and
migrate through the lymphatic system and target specific antigens via antibodies, receptors and toxin release
Causes of Inflammation
InjuriesExposure to microbes/pathogensExposure to foreign objects or chemicals (insect bites, stings, medications, etc)Exposure to allergens (pollen, pet dander, foods, etc)Rare: sunlight, temperature, self!
The Inflammatory Response3 Steps:
1. Tissue damage = release of chemical signals~– Mast cells release chemicals known as Histamine &
Prostaglandins that trigger inflammation
2. Dilation increases permeability of capillaries~– Increased blood flow; leukocytes leak out to infected area– Delivery of clotting factors & antimicrobial proteins
3. Phagocytosis of pathogens~– WBC’s engulf microbes or damaged tissue– Fever: leukocyte-released chemicals increase body
temperature
Specific ImmunityAntigen: – a foreign molecule that elicits a
response from a lymphocyte
Lymphocyctes:– WBC’s that originate from stem cells in
bone marrow– B Cells (mature in bone marrow)– T Cells (mature in thymus)
Antibodies: – antigen-binding immunoglobulin,
produced by B cells
Antigen receptors: – membrane receptors on B and T cells
Ch. 43 Research:
Humoral vs. Cell-mediated Responses
B cells vs. T cells
Memory cells
Clonal selection
Autoimmune disease
T cells vs. B cells
T cells:– Mature in Thymus– Target antigen fragments bound to
MHC molecules on Infected Cells– Part of Cell Mediated Response
B cells:– Mature in Bone Marrow– Target in-tact Antigens– Part of Humoral Response
Humoral vs. Cell-Mediated
Humoral immunity
B cell activation
Production of antibodies
Defend against intact antigens free in the lymph and blood plasma– (bacteria, toxins, and viruses)
Humoral response: B cells
Stimulated by an antigen-presenting macrophage (WBC w/ a germ on it)
Activates Helper T cells
T cells secrete cytokine chemicals that activate B cells
B cells differentiate into memory B cells and antibody-producing plasma cells
Cytokines
Cytokine:– Proteins secreted by phagocytic cells
(macrophages, etc.) and T-helper cells– Activate Lymphocytes (B & T cells)
Humoral Response:
1. B cells activate.
2. Plasma cells secrete antibodies.
3. Antibodies attach to antigens.
4. Antigens agglutinate (stick together) & get disposed.
5. Macrophages phagocytose or lyse the cell.
Cell-mediated immunity
T cells are activated.
T cells bind to and/or lyse infected cells.
Defend against cells infected with bacteria, viruses, fungi, protozoa, parasites, even cancer!
Cell-Mediated
Cell-mediated Response
1) Cell surface molecules expose antigens (foreign proteins).
2) Cytotoxic T cell releases perforin, a protein that forms pores in the target cell membrane.– causes cell lysis and exposes pathogens to
circulating antibodies for disposal
Humoral ResponseCell Mediated Response
In Tact Antigens Antigens on Infected Cells
B Cell Activation T Cell Activation
Secrete antibodies that defend
against pathogens & toxins in
extracellular fluid
Defend against infected cells,
cancer and transplanted
tissues
Clonal SelectionClonal selection: – antigen-driven cloning of lymphocytes
Effector cells: – short-lived cells that combat the antigen initially
Memory cells: – long-lived cells that bear receptors for the antigen
and activate upon subsequent exposure.
Active vs. Passive ImmunityActive: natural exposure to antigens causes one’s own lymphocytes to activate and produce antibodies– May also be acquired by Immunizations
Passive: direct transfer of antibodies through placenta or mother’s milk
HIVHuman Immunodeficiency Virus
Causes AIDS (Acquired Immune Deficiency Virus)
HIV (a retrovirus) attacks helper T cells by binding with their cell receptor (CD4)
This impacts both the Humoral and Cell Mediated responses
Clonal Selection Hypothesis
Each lymphocyte bears one specific type of receptor.
Receptor/antigen binding is required for cell activation.
Activated lymphocytes divide and give rise to cells with identical receptors to the parent.– This is how your immune system “remembers” a
pathogen later!
Clonal Selection Hypothesis
First, those lymphocytes bearing receptors compatible to “self” tissues are destroyed (3)
Second, those bearing receptors that match foreign antigens are activated then cloned (5/6)
Self/Nonself Recognition
Self-tolerance: – Capacity to distinguish self from non-self
molecules
Autoimmune diseases: – Failure of self-tolerance mechanisms– Multiple sclerosis, lupus, rheumatoid arthritis,
insulin-dependent diabetes mellitus, Crohn’s disease
Abnormal immune functionAllergies: – hypersensitive responses to environmental antigens (allergens)– causes dilation and blood vessel permeability– Histamines are released from Mast cells
Autoimmune disease: – multiple sclerosis– Lupus– rheumatoid arthritis– insulin-dependent diabetes mellitus
Immunodeficiency disease: – SCIDS (bubble-boy)– A.I.D.S. (HIV)
Cancer & the Immune System
Tumor cells are targeted by both Cytotoxic T cells and Natural Killer (NK) cells
– How might some tumors escape detection??
Treg research: Article Review
What are “Regulatory T Cells” (Tregs)?
What is their role in immunity?
How might they be linked with cancer?– Article: “Regulatory T cells and tumour
immunity – observations in mice and men” by Gallimore and Godkin, 2007
Major Histocompatibility Complex
Aka: “MHC”
Cell surface proteins that display fragments of antigens or processed proteins on the cell surface
Epitope: – region of antigen surface
recognized by antibodies
Induction of Immune Responses
Primary immune response: – lymphocyte proliferation and differentiation the 1st
time the body is exposed to an antigen
Plasma cells: – antibody-producing B-cells
Secondary immune response: – immune response if the individual is exposed to
the same antigen at a later time~ Immunological memory
Types of ImmunoglobinsIgM: – 1st to circulate; indicates infection; too large to cross
placenta
IgG: – most abundant; crosses walls of blood vessels and placenta;
protects against bacteria, viruses, & toxins; activates complement
IgA: – produced by cells in mucous membranes; prevent
attachment of viruses/bacteria to epithelial surfaces; also found in saliva, tears, and perspiration
IgE: – very large; small quantity; releases histamines-allergic
reaction
Antibody-Mediated Antigen Disposal
Neutralization (opsonization): – antibody binds to and blocks antigen activity
Agglutination: – antigen clumping
Precipitation: – cross-linking of soluble antigens
Complement fixation: – lyses viruses and pathogenic cells & activates cell
surface proteins to break down the cell
Immunity in Health & DiseaseActive immunity:– natural: conferred immunity by recovering from disease
– artificial: immunization and vaccination; produces a primary response
Passive immunity: – transfer of immunity from one individual to another
– natural: mother to fetus; breast milk
– artificial: rabies antibodies
ABO & Rh blood groups (antigen presence)