OCTOBER 20, 2008
What is a pathogen?
Pathogen is any agent that causes diseases
“PATHO” means diseases
1. Virus – HIV, cold, flu
2. Bacteria – pneumonia, tuberculosis, meningitis
3. Protists – Malaria, Lyme diseases
Plasmodium-malaria causing HIV infecting a cell
bacteria found in mosquito
The Immune system is the
body’s main defense against
The immune system recognizes,
attacks, destroys, and
remembers each type of pathogen
that enters the body.
Immunity- the process of the
immune system fighting
The immune system has two categories of defense
mechanisms against infection:
1. Nonspecific defenses
• Like fortress walls
• Guard against infection
by keeping most of things
out of the body
2. Specific defenses
• Like security guards
• Track down harmful pathogens
that managed to break through
the body’s nonspecific defenses
NONSPECIFIC defenses do not discriminate between one threat
1. First line of defense:
Function-to keep pathogens out of the body
Skin works as a barrier against infection
Most pathogens cannot penetrate through the skin’s surface
SECTRETIONS FROM THE BODY
The body secretes mucus, saliva, and tears which all contain
lysosomes to break down the cell walls of bacteria, and oil
and sweat which produce an acidic environment.
2. Second line of defense:
A non-specific defense reaction to tissue damage caused by injury
(broken/sprained bone, bump on the head) or infection (infected cut or
When your body releases chemicals that increase the body’s core
temperature and speed up your heart rate.
Increased body temperature is advantageous because many pathogens can
not survive at high temperatures, and increased heart rate helps white
blood cells get to the site of infection faster.
“Good fences make good neighbors”
The largest organ of the body – a covering over the entire body.
Epidermis – the outer layer of the skin
• Outside of epidermis is made up of dead cells
• Inner layer is made up of living cells
Dermis – the inner layer of the skin
• Under the epidermis
• Contains blood vessels, nerve endings, sensory receptors,
hair follicles, sweat glands, etc.
(Answer all questions in complete sentences)
1. What are the four “jobs” of your body’s immune
2. Use an analogy to explain the two different levels of
your immune system.
3. What is your body’s main defense against
4. What is one response that your second line of
defense has towards infection or injury.
If a pathogen is able to get past the body’s nonspecific defenses, the immune
system reacts with specific defenses
Specific defenses that attack the particular pathogen (disease-causing
agent) are called immune responses
This is triggered by antigen
What is an antigen?
Anything that triggers immune response – like an ID card of pathogens
(ex: virus, bacteria, other pathogens)
Each pathogen has its own antigen
When a pathogen invades the body, B cells recognize its antigen
B cells then grow and divide (reproduce) rapidly
Some B cells grow and become plasma cells
Some B cells grow and become memory B cells
Plasma cells immediately respond
to the infection by releasing antibodies
What are Antibodies?
Antibodies are proteins that recognize and bind to antigens
What do antibodies do?
Antibodies are carried in the bloodstream to attack the
pathogen (what is causing the infection).
Antibodies overcome the infection in one of two ways:
They kill the antigen directly.
They signal other immune cells (like white
blood cells and macrophages) that antigens
are present in the body.
Memory B cells
Long term immunity
Once the body has been exposed to a pathogen, many memory
B cells remain capable of producing antibodies specific to that
The reaction to a second infection by the same pathogen is