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

17
(No Transcript)
18
(No Transcript)