The body’s defenders
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Transcript of The body’s defenders
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
• chemokines• class I MHC• class II MHC• clonal selection• complement fixation• complement system• cytokine• cytotoxic T cell• effector cell• eosinophils• helper T cell• histamine• HIV• humoral immunity• immunity• immunodeficiency disease• immunoglobulin• inflammatory response• interferon• interleukin• lysozyme• macrophages• major histocompatibility
complex• mast cells• membrane attack complex
• memory cell• monocytes• natural killer cells• neutrophils• nonspecific defense• opportunistic disease• passive immunity pathogen• perforin• phagocytosis• plasma cell• primary immune response• prostaglandins• pyrogens• Rh factor• secondary immune
response• suppressor T cell• T cell• T cell receptor• target cell• tumor antigen• vaccine
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
SkinMucous 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
Tears
Mucus, cilia
Skin, oil,
sweat, acidity
Mouth bacteria,
saliva
Gastric juice
Intestinal flora
Acid conditions
Microbes
MACROPHAGE
Vacuole Lysosomecontainingenzymes
Phagocytic cellInnate immunity Second line: Internal defenses
Phagocytes Attach to and ingest invading
microorganisms Initiate the inflammatory
response Macrophages – migrants or in lymph
organs, lungs, kidneys, connective tissues Antimicrobial proteins
Complement system – lysis of invading cells, triggers inflammation
Interferons – activate macrophages, prevent cell-to-cell spread of viruses
Defensins – secreted by macrophages to damage pathogens
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70%chemotaxis
5% 1.5% histamine
Innate immunity Second line: Internal defenses (con’t.) Inflammatory response
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Chemicals involved• Histamines• Prostaglandins• Chemokines• Pyrogens
Innate immunity Second line: Internal defenses (con’t.)
Natural killer (NK) cells Attack virus-infected body
cells and cancer cells Apoptosis (cell death) in
cells attacked Coelomocytes and
hemocytes – phagocytes in invertebrates
Specific (acquired) immunityThird line of defense
Lymphocytes In blood and lymph Types
1. B – cells – mature in marrow2. T – cells – mature in thymus
Helper Cytotoxic/Killer Regulatory/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 cells
2) long-lived memory cells
MHC molecules and T cell function Class I MHC molecules
Most nucleated cells of the body Infected/cancerous cells display parts
of foreign antigens on surfaces Recognized by cytotoxic T cells
Class II MHC molecules Dendritic 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
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Clonal selectionantigen-driven cloning of
lymphocytes
Antigen binds to receptor on lymphocyte
Lymphocyte is activated
Thousands of clones specific for the antigen are produced
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 (artificial immunity)
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 (artificial immunity)
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 (SLE, diabetes type I, rheumatoid arthritis)
Immunodeficient diseases Inborn or primary (severe
combined ID) Acquired or secondary
AIDS – HIV attacks CD4 molecules on helper T cells, macrophages, dendritic cells
IgE antibodies bind to receptors or mast cells.
1On subsequent exposure to the same allergen, IgE molecules attached to a mast cell recog-nize and bind the allergen.
2Degranulation of the cell,triggered by cross-linking of adjacent IgE molecules, releases histamine and other chemicals, leading to allergysymptoms.
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Allergen
IgE
Histamine
GranuleMast cell