The Immune System and Disease
Bacteria and viruses are all around us, so
why are we not sick all of the time?
• Our bodies have a series of defenses that
guard against disease.
• The
immune system
is the body’s main
defense against pathogens
• The immune system is made up of two
defense mechanisms against disease:
Nonspecific Responses
First Line of Defense – Skin and Mucous Membranes
Keep Pathogens Out!
• Nonspecific defense (the first line of defense) reacts in the same manner to all pathogens.
• A mucous membrane is impermeable to most pathogens. Ex. Nasal passages, mouth, eyes, anus, etc.
Second Line of Defense
The Inflammatory Response
- Reaction to tissue damage
- If pathogens do enter the body, white blood cells (WBC) are used as the next defenders. WBC’s are also called
Two Types of Leukocytes
1. Phagocytes (fah-guh-sytes)
– Used for short minor invasions.
– They cause an inflammatory response - red, swelling, hot, fever - that usually can repel most small infections.
– They chew up invaders- (Phagocytosis).
• Lymphocytes (lim-fuh-sytes)
– Allow the body to remember and recognize previous invaders. Used for longer, more serious, invasions.
– We refer to their actions as the immune response. – There are 2 types, T-cells and B-cells.
The Inflammatory Response
Skin Wound
Bacteria enter the wound
Phagocytes move into the area and engulf the bacteria and cell debris
Specific Defense
The Immune Response
• A series of steps through which the
immune system attacks organisms and
substances that invade our bodies and
cause disease
• The immune response is the body’s main
line of defense and it includes
Macrophages and Antigens
• Your body’s cells are identified by marker proteins. • Antigens are “non-self” marker proteins found on
foreign invaders that cause an immune response.
• When macrophages find these antigens they destroy the pathogen.
– The macrophages save some of the invader’s
marker protein and display it on their surface like a wanted poster to call other WBC’s into action.
– This marks all cells in your body with that antigen as a target for elimination.
• Once the macrophage has sent out a marker alert the
B-Cell Lymphocytes
Humoral Immunity
• B-cells attack the actual invading pathogen or foreign agent. They provide immunity in body fluids.
• When a pathogen invades some B cells recognize the antigen and divide rapidly to produce Plasma cells.
• Plasma cells release antibodies that attack the pathogen.
• Some B-cells divide to make memory cells that will fight against future attacks
Structure of an Antibody
Antigen-binding
sites
T-Cell Lymphocytes
• T-cells attack infected cells in a process called cell-mediated immunity.
• Macrophages ingest the invader and display the antigens on their cell surface
•
There are 3 types:
– T-helper: circulate in your blood and lymph and control the immune response and direct other T-cells or B T-cells.
– T-killer: recognize and bind to one specific antigen. Killer T cells destroy infected cells only. They do not destroy the pathogens themselves.
Pacing the Immune Response
and Immunity
•
Primary Immune Response
– The first exposure to a pathogen.
– The body requires several days to form
Secondary Immune Response
• The next exposure to a pathogen.
– Future attacks to the same antigen are rapid because of memory cells, which are T-helper, T-killer,
B-cells, that are part of the army but don’t fight in the original infection. They can circulate for the rest of your life waiting for another battle.
• If the body gets invaded by the same pathogen
again, the memory cells produce antibodies that
are stronger and last longer than the original
Immunity
• The process of warding off disease
through antibodies.
• Immunity prevents a person from getting
certain diseases, like measles or
Active vs. Passive Immunity
• Active Immunity
– immunity by vaccination
– body makes its own antibodies in response to an antigen
• Passive Immunity
– when antibodies to an antigen are made in an animals body
– lasts only a short time, because the body
destroys the foreign antibodies
Problems with the Immune
System
•
Allergies
•
Autoimmune Diseases
Allergies
• An immune system response against a
non-pathogenic antigen called an
allergen
.
• Ex. Pollen, certain foods, dust, etc.
– Your body produces many more antibodies to the pollen antigen than it needs.
– The antibodies bind to the antigen and trigger a strong inflammatory response.
– Cells in your nose release a chemical messenger,
histamine, which causes swelling and release of fluid.
Autoimmune Diseases
• Result when the body manufactures
“anti-self” antibodies, and attacks its own cells.
• Ex.
Multiple Sclerosis
(MS) destroys the
myelin sheath that insulates and covers
Immune Deficiency
• The body may lose its ability to attack invading microorganisms and diseased cells.
– HIV (Human Immunodeficiency Virus) attacks the immune system. It invades macrophages and helper T-cells.
– HIV transforms these cells into virus factories which kills a large number of T-cells.
– The immune response cannot occur without helper T-cells directing B-cells and Killer T-cells.
– The body becomes overrun with pathogens and cancers that the body could normally fight off.
– A person has AIDS (Acquired Immune Deficiency Syndrome)
Stages of HIV Infection
Infection; Immune system eliminates most of HIV
Symptoms, such as swollen lymph nodes, are few
Loss of immune function more