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Ch 43- Immune system. Immune system. Defends body against disease Pathogens – agents of disease (bacteria, viruses, protists ) Non specific immunity (innate immunity) All animals & plants have defenses effective immediately upon infection Specific immunity (adaptive or acquired immunity)

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immune system
Immune system
  • Defends body against disease
    • Pathogens – agents of disease (bacteria, viruses, protists)
  • Non specific immunity (innate immunity)
    • All animals & plants have defenses effective immediately upon infection
  • Specific immunity
  • (adaptive or acquired immunity)
    • All vertebrates have immunity after exposure to pathogens (slower response).
1 non specific immunity
1. Non-specific Immunity
  • 1st line of defense: barrier
  • Skin, mucous membrane, secretions
  • 2nd line of defense: internal defenses
  • Phagocytosis, natural killer cells, antimicrobial proteins, inflammatory response
invertebrate defenses
Invertebrate defenses
  • 1st barrier – exoskeleton made of chitin
  • Digestive system is protected by a chitin-based barrier and lysozyme, an enzyme that breaks down bacterial cell walls
  • The immune system recognizes bacteria and fungi by structures on their cell walls
slide5

Pathogen

Hemocytes

- circulate within hemolymph and carry out phagocytosis, the ingestion and digestion of foreign substances including bacteria

- also secrete antimicrobial peptides that disrupt the plasma membranes of fungi and bacteria

PHAGOCYTICCELL

Vacuole

Lysosomecontainingenzymes

non specific immunity in vertebrates
Non-specific immunity in Vertebrates
  • Include barrier defenses, phagocytosis, antimicrobial peptides
  • Unique to vertebrates: natural killer cells, interferons, inflammatory response
barrier defenses
Barrier defenses
  • Skin
  • Mucous membranes
  • Body secretions: saliva ,mucus, tears
  • Low pH in skin & membranes
phagocytosis
Phagocytosis
  • “cell eating” – white blood cells ingest invading pathogens
  • Neutrophils – short lived white blood cells
  • Macrophages – largest phagocytes (from monocytes)
    • Engulfs microbe & fuses with lysosyme to destroy it
    • Found fixed in parts of lymphatic system (spleen, lymph nodes, thymus)
    • Some travel throughout body
  • Eosinophils – attack larger parasites
slide9

Phagocytes recognize groups of pathogens with Toll-like receptors (TLRs) that recognize molecular patterns characteristic of certain pathogens

  • This increases efficiency of phagocytes
    • i.e. double stranded RNA (in viruses)
      • Flagellin – protein found in bacteria flagella
slide10

Natural killer cells

  • Destroy virus-infected body cells
  • Attack cells membrane, so cell lyses
  • Lymphatic system involved in cellular non-specific defense
  • Lymph nodes hold many macrophages
slide11

Interstitialfluid

Bloodcapillary

Adenoid

Tonsils

Lymphaticvessels

Thymus

Lymphatic vessel

Tissuecells

Lymphatic vessel

Spleen

Lymphnodes

Lymphnode

Masses ofdefensive cells

antimicrobial proteins
Antimicrobial proteins
  • Proteins involved in attacking microbes or stopping their reproduction
  • Lysozyme- present in tears & saliva, mucous
  • Complement proteins – 20 serum proteins – carry out steps to lyse microbes
  • Interferons – secreted by virus-infected cells, induce neighboring cells to produce chemicals to inhibit viral reproduction
inflammatory response
Inflammatory response
  • Response to cut or entry of microorganisms
  • Area becomes inflamed, red, swollen
  • Result of chemical signals-
    • From invader
    • Nearby mast cells release histamines – released by body cells in response to injury
    • Histamines dilate capillaries and increase permeability, so fluid & clotting elements leave can enter site
inflammatory response1
Inflammatory response

Pathogen

Splinter

Movementof fluid

Macro-phage

Signalingmolecules

Mastcell

Phagocytosis

Capillary

Neutrophil

Redblood cells

slide15

Clotting begins

  • Other cells release chemokines, which attract phagocytes to area
  • Phagocytes consume pathogens & debris
  • Pus - a fluid rich in white blood cells, dead pathogens, and cell debris from damaged tissues

http://www.youtube.com/watch?v=CmbWE3jLUgM&list=UUDwoLF9pXx4RgB7BgmsnY0w

2 specific immunity
2. Specific Immunity
  • Specific immune responses to particular microorganisms
  • Found in vertebrates
  • Lymphocytes – type of white blood cells
    • 2 types:
    • T cells – mature in thymus
    • B cells – mature in bone marrow
antigens
Antigens
  • Substances that can elicit a response from a B or T cell
  • B or T cells have antigen receptors specific for parts of that pathogen – so they can recognize specific antigens

Antigen receptors

Mature B cell

Mature T cell

slide20

The specificity of the T & B receptors (and antibodies) is a result of shuffling and recombining several gene segments to produce the protein

  • There are more than 1 million different B cells and 10 million different T cells
  • Due to random arrangment, some receptors are specific for epitopes on organism’s own molecules, so B & T cells must be tested for self- reactivity.
slide22

B cells:

  • Mature in bone marrow
  • Produce antibodies
  • Receptors bind to intact antigens
  • T cells:
  • Mature in thymus
  • Do not produce antibodies
  • Receptors bind to antigens displayed by antigen-presenting cells (APCs) on their MHCs

Both:

Activated by cytokines, from helper T cells

slide23

MHC – major histocompatability complex – cell surface glycoproteins that differ among individuals

- aid in recognition of “self”

- Class I – found on nearly all body cells

- can present fragments of proteins made by infecting microbes to cytotoxic T cells

- Class II – made by some cells of immune system

- macrophages & B cells

- molecules collect remnants of microbes and present them to helper T cells

clonal selection
Clonal selection
  • Activation occurs when antigen binds to B or T cell.
  • Clones formed in clonal selection – two types produced:
    • Effector cells – fight the antigen
    • Memory cells – have receptors for same antigen, so allow quick response to subsequent infection
    • http://www.youtube.com/watch?v=HUSDvSknIgI
responses
Responses
  • Primary response- when body first exposed to antigen and lymphocyte is activated
  • Secondary response – when same antigen is encountered later, faster more efficient response due to memory cells
slide26

Primary immune responseto antigen A producesantibodies to A.

Secondary immune response toantigen A produces antibodies to A;primary immune response to antigenB produces antibodies to B.

104

103

Antibodiesto A

Antibody concentration(arbitrary units)

Antibodiesto B

102

101

100

7

35

56

49

0

14

21

28

42

Exposure to antigens A and B

Exposureto antigen A

Time (days)

cell mediated immunity
Cell- mediated immunity
  • Activation & clonal selection of cytotoxic T- cells
  • Macrophages engulf antigens, process them internally, then display parts of them on their surface together with some of their own proteins. This sensitizes the T cells to recognize these antigens.
slide28

T-cells are trained in thymus

  • T- cells are chosen that have correct receptors to recognize MHC molecules
  • T- cells that can recognize MHC molecules complexed with foreign peptide are allowed to pass out of thymus
slide29

Cytotoxic T cells (Killer T cells) bind to class 1 MHC molecules, display fragments on surface of body cells. Destroy infected cells.

  • Helper T-cells: secrete cytokines in response to interaction with class 2 MHC molecules – stimulate & activate both cytotoxic T cells & B cells
  • Memory T cells – recognize & respond to antigen once it has already been encountered.
  • http://www.youtube.com/watch?v=1tBOmG0QMbA
humoral response
Humoral response
  • Activation & clonal selection of effector B cells
  • Fight pathogens in body fluids
  • Activated B cells produce plasma & memory cells
  • Plasma cells –(effector cells) produce antibodies
  • Memory cells – for secondary response
slide31

Antibodies – soluble proteins secreted by B cells during an immune response

  • Antibodies destroy antigens through:
    • Neutralization: bind & block activity of antigen
    • Lysis: caused by activation of complement system- form a hole in membrane of pathogen
    • Agglutination: clumping of bacteria or viruses
    • Opsonization: results in increased phagocytosis of antigen (attracts macrophages)
slide32

Humoral response:

  • http://www.youtube.com/watch?v=hQmaPwP0KRI&list=UUDwoLF9pXx4RgB7BgmsnY0w&index=7
  • Specific immunity
  • http://www.dnatube.com/video/194/Specific-Adaptive-immunity-humoral-and-cell-mediated
slide33

Active immunity – when body is exposed directly to pathogen, body responds

  • (infection, vaccination)
  • Passive immunity – when an individual receives antibodies
  • (to fetus from mother across placenta)
slide34

Allergy reaction animation

  • http://www.youtube.com/watch?v=IGDXNHMwcVs
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