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Defense against Disease

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Defense against Disease Non-specific and specific strategies – PowerPoint PPT presentation

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Title: Defense against Disease


1
Defense against Disease
  • Non-specific and specific strategies

2
Inherent Challenges
  • Constant surveillance and vigilance
  • Unpredictable invaders

3
The Enemy
  • Pathogens microorganisms that are capable of
    causing disease
  • Viruses
  • Bacteria
  • Fungi

4
Public Enemy 1The Viruses
  • Modus Operandi
  • Dock with receptors on target cell surface
  • Insert viral DNA or RNA into host cell
  • Use host cell machinery to replicate new
    viruses
  • Lyse host cell and spread to nearby cells
  • Lytic vs. Lysogenic life cycles
  • Examples smallpox, chickenpox, polio, HIV

5
Public Enemy 2Bacteria
  • Modus operandi
  • Set up shop in tissues but remain EXTERNAL
    to cells
  • Reproduce rapidly
  • Secrete exotoxins or contain endotoxins as
    part of cell wall
  • Examples Escherichia coli, Clostridium
    botulinum, Salmonella

Figure from Holt Biosources
6
Public Enemy 3Fungi
  • Modus Operandi
  • Similar to bacteria-
  • reproduce rapidly
  • Damage cells directly or indirectly
  • by secreting enzymes
  • Examples Athletes Foot,
  • Pneumocystis carinii (fungal pneumonia)

http//www.ces.ncsu.edu/depts/pp/bluemold/
7
So whats a body to do?
  • First line defenses Nonspecific anatomical
    barriers and secretions that prevent entry, such
    as skin, saliva, tears (lysozyme), mucus, stomach
    acid, fever
  • Second line defenses Inflammation
  • A nonspecific response triggered by histamine
    secreted by basophils when tissue is damaged

8
If all else failsThe Immune Response
  • A highly specific, long lasting response tailored
    to combat pathogens
  • Vocabulary
  • Antigen- a molecule (usually carried on the
    surface of a pathogen) that is capable of
    eliciting an immune response
  • B-Lymphocytes- white blood cells that produce
    and secrete antibodies
  • T-Lymphocytes- white blood cells that serve as
    part of the cell-mediated immune response

9
Self- Nonself Recognition
  • Critical to appropriate immune system function
  • Tcells learn to distinguish self from non self
    as they mature in the thymus
  • All nucleated self cells display unique Human
    Leukocyte Antigens (HLA) on their Major
    Histocompatibility Complex (MHC) receptors
  • As T cells mature, they randomly produce and
    display a variety of receptors
  • Any T cell with receptors that bind to self
    MHC-HLA complexes will commit apoptosis
  • Only T cells that do NOT bind to self cells
    should emerge from the thymus and enter
    circulation

10
The Immune Response - Overview
11
Immune Response- Step by Step
1. Pathogen (carrying foreign antigens) enters
and survives the inflammatory response 2. Some
pathogens remain exposed in tissues where their
antigens may be recognized by circulating B
cells OR 3. Macrophages engulf pathogens and
display their antigens on MHC (major
histocompatibility complex) receptors. Macrophage
has now become an Antigen Presenting Cell (APC)
12
Central Role of Helper T Cells
13
Humoral ImmunityB cell response
  • If a circulating B cells receptors bind to
    foreign antigens, the B cell becomes activated
  • Activated B cells divide into Memory B cells and
    Plasma B cells
  • Plasma B cells rapidly produce and secrete
    antibodies (immunoglobulins)
  • Clonal selection amplifies the production of
    cells that produce effective antibodies

14
Clonal Selection
Figure from AccessExcellence.org
15
Mechanism of Antibody Function
  • Antibodies bind to antigens and aggregate
    pathogens for removal by macrophages
  • Antibodies disrupt function of pathogens surface
    proteins
  • Antibody-antigen complexes trigger the Complement
    system, a a series of enzymes carried in the
    bloodstream that lyse invaders

Figure from AccessExcellence.org
16
Cell-Mediated ImmunityT cell Response
  • Helper T cells (a.k.a. TH or CD-4 T cells)
    constantly interact with macrophages
  • When TH cell finds a macrophage that is
    presenting antigen (APC) it becomes activated
  • Activated TH cells secrete cytokines, chemicals
    that stimulate both T and B cells
  • Stimulated cytotoxic T cells (a.k.a. killer or
    CD-8 T cells) divide rapidly, bind directly to
    pathogen infected cells and secrete enzymes that
    lyse infected cells

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