Immunity and Disease

Disease• Infection = when a microorganism or pathogen gets into

our body.– Pathogen: anything that causes disease.– Microbe/Microorganism: living entity that can cause disease.

• Disease = a change that interferes with bodies ability to maintain homeostasis.• Infectious disease: can be passed from one person to another.

– This means the disease is contagious: a disease that can be transmitted.

– Examples include: Flu, cold, STD’s, HIV• Not all diseases are infectious for example cancer is a disease

(change from homeostasis), but it can not be transmitted to someone else.

Common Pathogens• Viruses: common cold, flu, rabies, HIV• Bacteria: strep and staph• Fungi: athlete’s foot and ringworm• Parasitic worms: hookworm• Protozoa: malaria, sleeping sickness• Toxins: botulism, venom, stings

Common Pathogens

• Toxin: any substance that is poisonous.• Many diseases can be carried via vectors.– Vector: a living creature that can carry disease from one

individual to another.• Mosquitoes, ticks, fleas, etc…

• Certain risk factors can make someone more susceptible to certain diseases.– Genetics (inheritance)– Organ malfunction– Overexposure– Dangerous Behaviors`1

Body Defenses

• The body is constantly in contact with pathogens.• The body has two defense systems for foreign

antigens.– Innate (nonspecific) defense system– Adaptive (specific) defense system

• Immunity—specific resistance to a disease.

Immune System

For non-specific defense, the response is always the same no matter what the disease causing agent is.

Innate Body Defenses

• Innate body defenses are mechanical barriers to pathogens such as:– Body surface coverings

• Intact skin - pH of the skin is acidic to inhibit bacterial growth

– Mucous membranes• Stomach mucosa - secretes hydrochloric acid

– Mucus traps microogranisms in digestive and respiratory pathways

Cells and Chemicals:Second Line of Defense

• Phagocytes: cells that engulf foreign microbes.– Macrophage: type of white blood cell that acts as a

phagocyte.• Inflammatory response: triggered when body

tissue is injured, develops redness, swelling, pain.– This response designed to increase blood flow to an

area • Fever: abnormally high body temperature.– High temperatures inhibit the release of iron and zinc

from the liver and spleen needed by bacteria.

Adaptive Defense System: Third Line of Defense

• This type is specific to the threat and is a whole body response

• Immune response: body uses specialized immune cells to respond to a threat (foreign antigen).

• Antibodies: are special proteins that protect us from pathogens. Identify foreign antigens

• Three aspects of adaptive defense– Antigen specific—recognizes and acts against particular

foreign substances– Systemic—not restricted to the initial infection site– Memory—recognizes and mounts a stronger attack on

previously encountered pathogens.

Adaptive Defense System: Third Line of Defense

• Types of Immunity – Humoral immunity = antibody-mediated immunity• Provided by antibodies present in body fluids that seek

out foreign antigens• B-cells: are a special type of white blood cell that

mature in the bone marrow, they make antibodies.– Cellular immunity = cell-mediated immunity• Targets virus-infected cells, cancer cells, and cells of

foreign grafts• T-cells: are a special type of white blood cell that

mature in the thymus, they direct cell-mediated immunity.

Humoral (Antibody-Mediated) Immune Response

• B cell have a specific receptor that is looking for a specific antigen.– For example if you have had chicken pox before you have

antibodies that are looking for that specific virus, but those antibodies will not protect you from other viruses like HIV

• If the B cell finds a virus that it matches to it will make clones of itself.

• Half of the clones with go out into the blood and fight off the pathogen as antibodies.

• The other half will become memory cells that stay in your body in case the pathogen comes back again.

Cellular (Cell-Mediated) Immune Response

• If a T cell matches up with an antigen like with the B cells it also makes clones:– Cytotoxic (killer) T cells• Specialize in killing infected cells.• Insert a toxic chemical that kills the cell.

– Helper T cells• Recruit other cells to fight the invaders.• Interact directly with B cells.

– Suppressor T cells turn off the immune response once the pathogen has been removed.

A Cytotoxic T Cell Touch-Killing a Tumor Cell

Immune Response

1. Chicken pox virus gets into the body past the skin and mucous membranes into your blood.

2. Macrophages recognize the foreign antigen and “eat” it, this kills the virus.

3. The macrophage then takes some of the virus antigen and puts it on the outside of its cell membrane to tell other cells what it found.

4. The macrophage circulates in the blood until it meets up with a helper T – cell that is specific for the chicken pox virus.

Immune Response

4. The helper T cell activates 3 main things:– Chicken pox B cells that make chicken pox antibodies.– Chicken pox killer T cells that kill the virus directly.– More helper T cells that can activate B and T cells.

5. Once the infection is done the suppressor T cells turn off the response.

6. Chicken pox memory T and B cells circulate in case the virus comes back.