The Incredible Immune System

Or....

Why you're

not dead.

Who are these guys...

and why are they trying to

hurt (not kill) us?

PATHOGENS

∙Bacteria

∙Protists

∙Fungi

∙Parasites

∙Viruses

Bacteria

Warmth

Moisture

Nutrition

Protists

Warmth

Moisture

Nutrition

Fungi

Warmth

Moisture

Nutrition

Parasitic worms

and arthropods

Tapeworm

Ascaris

Filarial worm

Warmth

Moisture

Nutrition

Viruses

SPREAD OF PATHOGENS

∙food and water borne

∙air-borne...droplet infection (sneeze/cough)

∙contact infection

∙wound infection

∙arthropod carriers (insects and relatives)

HISTORICALLY INCREASED BY:

Global trade

Better transportation

Urbanization

Factory work

Public schools

GREATLY REDUCED BY:

Shoes

Pasteurization

Window screens

Air conditioning

Clean water!!!

Better hygiene, nutrition

Non-contaminated food

Antitoxins & vaccines

SELF VS. NON-SELF

∙organisms are biochemically unique

∙There are proteins on surface of every

cell...harmless to self; provoke a reaction within

another body

∙different in each individual

∙antigen = substance capable of stimulating a

response

FACTORS AFFECTING IMMUNITY

∙age

∙genetics

∙hormonal effects

∙physiological state

∙portal of entry

∙virulence of antigen

∙stress

∙NON-SPECIFIC (first line)

∙skin

∙respiratory system

∙ears

∙eyes

∙mouth

∙stomach

∙urogenital tract

∙Interferons

second line of defense

∙local inflammatory response

∙mast cells release histamines

∙cause pain, heat, redness, swelling

∙cause constriction of some smooth muscles

(bronchioles)

∙blood vessels dilate...increase flow to area

∙cause permeability of capillaries to increase

∙serotonin

∙its action resembles histamine, but it causes

vasoconstriction of larger blood vessels

∙cytokines can also be produced if a virus is present

∙cytokines inhibit production of viruses

∙general inflammatory response

(fever)

∙macrophages release interleukine

∙reset body’s thermostat in

hypothalamus

∙may be a way to slow down until

immune system can catch up

∙phagocytosis

∙increased blood flow brings large

numbers of neutrophils and monocytes

∙NK (natural killer) cells

∙kill virally infected cells

∙may attack tumor and other

cancerous cells

3rd Line of Defense: SPECIFIC - Takes several days to

activate

∙cells of this system must be able to distinguish between

self and non-self

∙proteins on cell surface membranes act as recognition

devices, called antigens

∙immune system is tolerant to the body’s own antigens

and does not attract them

∙There are two types of responses: cell mediated and

antibody mediated

Cell-Mediated Immunity (T-cells)

∙Macrophages engulf pathogens and bring them to lymphocytes

∙their information is “presented” to helper T-cells

∙Helper T-cells

∙Killer T-cells

∙Memory cells

∙Suppressor cells

Helper T-cells

∙make other lymphocytes competent

∙can stimulate B-cells to become plasma cells to make

antibodies

∙stimulate the production of other T and B cells

∙produce lymphokines which stimulate macrophages to

engulf more invading cells

∙can produce interleukines

∙enhance inflammation

∙stimulate killer T-cells

Killer T-cells

∙combine with antigens

∙attack cancer cells

∙cannot attack viruses directly, but can destroy cells

containing viruses

∙Once a virus enters a cell, it is safe from

antibodies.

∙Only T-cells destroying the cell can destroy the

virus

∙Cells containing viruses have viral antigens on

their surface...they can be recognized

∙release lymphokines

Memory cells

∙live for years in the lymphatic system

∙Memory T & B cells circulate in the lymph, ready to react with

their antigen

∙Antigens entering the body are carried by macrophages to a

lymphatic organ (spleen, tonsils, lymph nodes) where there is

a high conc. of T cells

∙Sometimes, swelling in nodes indicates an infection

∙At a second exposure, the response proceeds more rapidly

∙Pathogens are usually destroyed before they can cause any

symptoms

∙prevent you from getting the same disease twice

∙Suppressor cells

∙reproduce slowly (1 week)

∙inhibit other cells

∙help prevent immune system

from

over-reacting to a stimulus

∙Antibody-mediated immunity. (B-

lymphocytes)

∙After a macrophage has ingested a

pathogen, helper T-cells are activated as

before

∙The helper T-cells trigger specific B-

cells to proliferate and differentiate into

plasma cells

∙B-cells

∙divide through mitosis and differentiate into

plasma cells

∙Plasma cells produce antibodies

∙Plasma cells do not leave the lymph nodes

∙The antibodies they produce travel to the

infected area

∙an antibody is a globular protein that reacts to a

specific antigen

∙antibodies work to destroy antigens several

ways

∙agglutination

∙some produce antitoxins

∙lysis

∙some coat the pathogen

∙some stimulate phagocytosis

∙some stimulate the compliment system

∙Some B-cells produce memory cells

∙AIDS = deficiency of t-lymphocytes

∙HIV attacks helper T-cells

∙results in abnormally high ratio of

suppressor T-cells to helper T-cells

∙suppressors inhibit secretions of killer

T-cells

∙and inhibit development of B-cells into

plasma cells

Types of Immunities

∙Active: antibody-antigen or T-cells react to antigen

∙natural: natural exposure to pathogen

∙artificial

∙exposure to dead or weakened pathogen (oral,

injection)

∙Passive: person is given antibodies

∙natural: person is given antibodies across

placenta/colostrum from mother

∙artificial: injection of antibodies produced in another

animal

Hypersensitivity

∙allergies: mild antigens induce a response which

non-allergic people don’t respond to

∙When exposed to allergen, Helper T-cells

stimulate B-cells to produce an antibody called

IgE (reagin)

∙IgE attaches to IgE receptors on mast cells

(large connective tissue cells) and basophils

∙Upon second exposure to allergen, it attaches to

IgE and causes mast cells to release large

amounts of histamines, causing inflammation,

edema, large amount of mucus secretion, etc.

Graft or transplant rejection

∙t-cell suppressors, like cyclosporin, are

used to reduce rejection of transplanted

organs

∙immunologically privileged sites

∙Sites where foreign tissue will not be

rejected

∙cornea, uterus