Date post: | 18-Oct-2014 |
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The body’s defenders
Core concepts Infectious diseases are caused by pathogens Nonspecific defenses against infection
Plants and animals have mechanisms that are not targeted to specific pathogens that help them combat infection
Skin and mucous membranes provide first-line barriers to infection Phagocytic cells, inflammation, and antimicrobial proteins function as the second line of defense
Specific immunity arises from lymphocyte-antigen interactions Lymphocytes provide the specificity and diversity of the immune system Antigens interact with specific lymphocytes, inducing immune responses and immunological
memory Lymphocyte development gives rise to an immune system that distinguishes self from nonself
Immune responses take two forms: humoral and cell-mediated Helper T-lymphocytes function in both humoral and cell-mediated immunity Cytotoxic T-cells counter intracellular pathogens B-cells make antibodies against extracellular pathogens Memory B- and T-cells are responsible for faster and stronger secondary immune responses
Immunity in health and disease Immunity can be achieved naturally or artificially The immune system limits blood transfusion and tissue transplantation Abnormal immune function can lead to disease AIDS is an immunodeficiency disease caused by a virus
Keywords ABO blood groups active immunity agglutination AIDS allergy anaphylactic shock antibody antigen antigen receptor antigen-presenting cell apoptosis autoimmune disease B cell basophils CD4 CD8 cell-mediated immunity
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Pathogens and disease
Fungi
Viruses
Protozoa
Bacteria Large parasites
Two major types of defenses
INNATE (NONSPECIFIC)IMMUNITY
Rapid responses to a broad range of microbes
ACQUIRED (SPECIFIC) IMMUNITY
Slower responses to
specific microbesExternal defenses Internal defenses
Skin
Mucous membranes
Secretions
Phagocytic cells
Antimicrobial proteins
Inflammatory response
Natural killer cells
Humoral response(antibodies)Cell-mediated response(cytotoxic lymphocytes)
Invadingmicrobes
(pathogens)
Innate (nonspecific) immunity First line: External defenses
External defenses
Microbes
MACROPHAGE
Vacuole Lysosomecontainingenzymes
Phagocytic cellInnate immunity Second line: Internal defenses Phagocytes
Attach to and ingest invading microorganisms
Initiates the inflammatory response○ Macrophages – migrants or in
lymph organs
Antimicrobial proteins Complement system – lysis of
invading cells, triggers inflammation Interferons – activate macrophages,
prevent cell-to-cell spread Defensins – secreted by macrophages
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Inflammatory response
Innate immunity Second line: Internal defenses (con’t.)
http://www.sumanasinc.com/webcontent/anisamples/dynamicillustrations/inflammatory.html
Chemicals involved• Histamines• Prostaglandins• Chemokines• Pyrogens
Innate immunity Second line: Internal defenses (con’t.)
Natural killer (NK) cellsAttack virus-infected
body cells and cancer cells
Apoptosis (cell death) in cells attacked
Coelomocytes and hemocytes – phagocytes in invertebrates
Specific (acquired) immunityThird line of defenseLymphocytes
In blood and lymph Types
1. B – cells – mature in marrow
2. T – cells – mature in thymus○ Helper○ Cytotoxic/Killer○ Suppressor○ Memory
Activated by cytokines from phagocytes
Display specificity to epitopes on antigens (antibody generator)
Have specific membrane-bound antigen-receptors
Two types of specific immune responses
B and T cells generate clones of1)short-lived activated effector cells2)long-lived memory cells
MHC molecules and T cell function
Class I MHC moleculesMost nucleated cells of the bodyInfected/cancerous cells display parts of
foreign antigens on surfacesRecognized by cytotoxic T cells
Class II MHC moleculesDendritic cells, macrophages, B cells
(APCs) display phagocytized antigen fragments on surfaces
Recognized by helper T cells T cells that have receptors for self-
molecules are destroyed self-tolerance
Antibody action
Immunity – memory cells initiate a faster, more efficient response upon reinfection
Active immunity Own system
develops antibodies Develops naturally in
response to infection Develops following
immunization Long-lasting
protection but may take a long time
Passive immunity Antibodies are passed
from mother to fetus via the placenta
Antibodies are passed from mother to infant via breast milk (colostrum)
Antibodies may be injected into a nonimmune person
Immediate, short-term protection
Blood groups and transfusions Problems with transfusions and transplants Antigens on RBC’s will determine a person’s
blood type: A, B, AB, O blood Another RBC antigen: Rh factor Rh+ or
Rh-
Immune disorders/diseases Allergies –
hypersensitive responses to antigens called allergens
Autoimmune diseases – immune system loses tolerance for self and turns against certain molecules of the body
Immunodeficient diseases Inborn or primary Acquired or secondary
○ AIDS – HIV attacks CD4 molecules on helper T cells
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