1. Fighting the Enemy Within!
phagocytic leukocyte
Fighting the Enemy Within!
The Immune System
Innate Immune System
lymph
system

2. Avenues of attack Points of entry Routes of attack digestive system
respiratory system
urogenital tract
break in skin
Routes of attack
circulatory system
lymph system

3. What’s in your lunchbox?
Why an immune system?
Attack from outside
lots of organisms want you for lunch!
animals are a tasty nutrient- & vitamin-packed meal
cells are packages of macromolecules
no cell wall
animals must defend themselves against invaders
viruses
HIV, flu, cold (rhinovirus), measles, chicken pox
bacteria
pneumonia, meningitis, tuberculosis, MRSA
fungi
yeast (“Athlete’s foot”…)
protists
amoeba, Lyme disease, malaria
Attack from inside
defend against abnormal body cells = cancers
Mmmmm,
What’s in your lunchbox?

4. Lymph system Production & transport of leukocytes
Traps foreign invaders
Lymph system
lymph vessels
(intertwined amongst blood vessels)
lymph node

5. Development of Red & White blood cells
Pluripotent = stem cell capable of giving rise to several different cell types
Development of Red & White blood cells
Red blood cells
inflammatory response
fight parasites (such as parasitic worms)
develop into macrophages
short-lived phagocytes
60-70% WBC

6. Bacteria & insects inherit resistance. Vertebrates acquire immunity!
Lines of defense
1st line: Barriers
broad, external defense
“walls & moats”
skin & mucus membranes
2nd line: Non-specific patrol
broad, internal defense
“patrolling soldiers”
leukocytes = phagocytic WBC
macrophages
3rd line: Immune system
specific, acquired immunity
“elite trained units”
lymphocytes & antibodies
B cells & T cells
Bacteria & insects inherit resistance.
Vertebrates acquire immunity!

7. 1st Line of Defense
BARRIERS

8. EXTERNAL DEFENSE Physical & chemical defenses external barrier
non-specific defense
external barrier
epithelial cells & mucus membranes
skin
respiratory system
digestive system
uro-genital tract
Lining of trachea: ciliated cells & mucus secreting cells

9. CHEMICAL BARRIERS ON EPITHELIUM
Skin & mucous membrane secretions
sweat
pH 3-5
tears
washing action
mucus
traps microbes
saliva
anti-bacterial = “lick your wounds”
stomach acid
pH 2
anti-microbial proteins
lysozyme enzyme (in saliva, mucus, and tears)
digests bacterial cell walls

10. CELLULAR INNATE DEFENSES
2nd Line of Defense
CELLULAR
INNATE DEFENSES

11. INTERNAL, BROAD RANGE CONTROL
Innate, general defense
RAPID response
Patrolling cells & proteins
attack invaders that penetrate body’s outer barriers
leukocytes
phagocytic white blood cells
complement system
~20 anti-microbial proteins
inflammatory response
leukocytes

12. Leukocytes: Phagocytic WBCs
Attracted by chemical signals released by damaged cells
enter infected tissue, engulf & ingest microbes
traps in a vacuole and fuses with a lysosome = nitric oxide poisons and enzymes degrade
Neutrophils
most abundant WBC (~70%) but short lived
engulf & destroy microbe
Macrophages
“big eater”, long-lived
some in spleen and lymph nodes
Dendritic cells: stimulate the development of acquired immunity (dendri = tree like)
Eosinophils
low phagocytic activity
defend against multicellular invaders (parasitic worms)

13. Phagocytes
macrophage
yeast

14. ANTIMICROBIAL PEPTIDES AND PROTEINS
Interferons
proteins provide innate defense against viruses
Virus-infected body cells secrete interferons
Nearby uninfected cells produce substances to “interfere” with the viral resproduction.
Limits cell-to-cell spread of virus

15. ANTIMICROBIAL PEPTIDES AND PROTEINS
Complement system
~20 proteins circulating in blood plasma
attack bacterial & fungal cells
form a membrane attack complex
perforate target cell
apoptosis
cell lysis
extracellular fluid
complement proteins form cellular lesion
plasma membrane of invading microbe
complement proteins
bacterial cell

16. INFLAMMATORY RESPONSE
Damage to tissue triggers local non-specific inflammatory response
release histamines & prostaglandins
capillaries dilate, more permeable (leaky)
increase blood supply
delivers WBC, RBC, platelets, clotting factors
fight pathogens
clot formation
accounts for swelling, redness & heat of inflammation & infection
Histamine is a compound that is released by cells in response to injury and in allergic and inflammatory reactions, causing contraction of smooth muscle and dilation of capillaries.
The prostaglandins (PG) are a group of physiologically active lipid compounds having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals.

17. Inflammatory response
Reaction to tissue damage
Pin or splinter
Blood clot
swelling
Bacteria
Chemical
alarm signals
Phagocytes
Blood vessel

18. Fever When a local response is not enough
systemic response to infection
activated macrophages release interleukin-1
triggers hypothalamus in brain to readjust body thermostat to raise body temperature
higher temperature helps defense
inhibits bacterial growth
stimulates phagocytosis
speeds up repair of tissues
causes liver & spleen to store iron, reducing blood iron levels
bacteria need large amounts of iron to grow
Certain bacterial infections can induce an overwhelming systemic inflammatory response leading to a condition known as septic shock.
Characterized by high fever and low blood pressure, septic shock is the most common cause of death in U.S. critical care units.
Clearly, while local inflammation is an essential step toward healing, widespread inflammation can be devastating.

19. Natural Killer Cells destroy virus-infected cells & cancer cells
patrol body and attach to “sick” cells
release chemicals that lead to cell death
inhibit spread of viruses and cancer

20. Destroying cells gone bad!
Natural Killer Cells perforate cells
release perforin protein
insert into membrane of target cell
forms pore allowing fluid to flow into cell
cell ruptures (lysis)
apoptosis
vesicle
natural killer cell
perforin
cell membrane
perforin punctures cell membrane
cell membrane
virus-infected cell