Download Rapid response to infection

Immune System
Continue reading Chapter 13 and Supp 14
Learning objectives
• What is a pathogen? What kinds of life forms can be
pathogens?
• What is meant by “3 lines of defense” against
pathogens?
• Explain how the first line of defense prevents entry of
pathogens. How does each work?
• Explain how the 2nd line is a general system that is
always ready, to respond to general threats.
• Explain how the 3rd line is very specific to the threat,
but takes time to respond.
• How are infectious diseases spread?
Pathogens
Virus
Helminths
Bacteria
Fungi
Protozoa
Ectoparasites
Major Players in the Immune System
• Skin
• White Blood Cells
• Lymphatic System
3 Lines of Defense
1. Surface barriers –
Skin and body
linings
2. Innate immune
system – Immediate
but generalized
response
3. Adaptive immune
system – Threatspecific response,
create “memory”
1st Line of Defense: Surface Barriers
• Skin: Acts as barrier,
secretes antimicrobial
substances
• Tears, saliva, mucous:
Contain lysozyme
• “Friendly Bacteria”:
Take space &
resources, produce
acids
2nd Line of Defense:
Innate Immune system
• Rapid response to infection
• Increased blood flow to infection site
• Neutrophils and Macrophages (types of WBC)
– Engulf pathogens
• Natural killer cells (WBC)
– Kill virus-infected and cancer cells
• WBCs release proteins that attract more WBCs
Chemical Signals Released by WBCs
• Complement proteins: kill invaders or flag
them for macrophages
• Cytokines: carry signals among cells
Pathogens have ANTIGENS that
identify them as ‘non-self’
3rd Line of Defense:
Acquired immunity
• Specificity: B and T cells (WBC) make receptors
for one type of antigen
• Diversity: Collectively, B and T cells have
receptors
for
at
least
a
billion
threats
rd
3 Line of Defense: Adaptive Immunity
• Memory: Some B and T cells held in reserve
Defining
Features
for future
infections
Specificity: Each B or T
cell makes receptors for
only one type of antigen
Diversity: Collectively, B
and T cells have
Antigen is recognized
• B and T cells divide rapidly
– Effector cells go for immediate attack
– Memory cells set aside for future threats
• B and T cells produce lots of antibodies
– Mark invaders as non-self and allow other cells to
destroy them.
Memory cells
•
•
•
•
Live long after infection heals
Keep body ‘primed’ to fight infection
Can mount very quick response
Kill pathogens before they have a chance to
reproduce much.
Lymphatic
System
Thymus Gland: T cells
specialize to combat specific
antigens
Spleen: Antibody production;
holding site for lymphocytes,
RBCs, and macrophages
Lymph Nodes: WBCs
accumulate; Filter pathogens
from lymph
Cytotoxic T cells cause rejection in
organ transplants
• Markers on cells
must match very
closely or they are
recognized as
antigens
• Immunosuppressant
drugs are necessary
Infectious Diseases
Modes of Transmission
•
•
•
•
Direct contact
Indirect contact
Inhaling pathogens
Contact with a vector
(something that
carries a pathogen
from infected person
to new host)
Patterns of Infectious Diseases
• Sporadic: irregular,
affects few
• Endemic: more or
less continuous
• Epidemic: disease
rate above
expected
• Pandemic: epidemic
in several countries