phagocytic
leukocyte
Fighting the
Enemy Within!
Immune
System
Big Questions:
1. What is the purpose of a immune system?
2. How does the immune system function?
3. Why do animals have a more developed immune
system?
AP Biology
Immune Systems
 Highly developed in

mammals
Two types of
immunity:
1.
2.
Innate immunity
(nonspecific)
Adaptive
immunity
(specific)
What about other organisms?
AP Biology
Lymphatic System: Production &
transport of leukocytes (WBC)
Traps foreign invaders
Lines of defense
 1st line: Non-specific barriers

broad, external defense
 “walls & moats”

skin & mucous membranes
 2nd line: Non-specific patrols

broad, internal defense
 “patrolling soldiers”

leukocytes = phagocytic WBC
 3rd line: True immune system

specific, adaptive immunity
 “elite trained units”

lymphocytes & antibodies
 B cells & T cells
AP Biology
Bacteria & insects
inherit resistance.
Vertebrates
acquire immunity.
1st line: Non-specific External defense
 Barrier
 skin
Lining of trachea:
ciliated cells & mucus
secreting cells
 Traps
 mucous membranes, cilia,
hair, earwax
 Elimination
 coughing, sneezing, urination,
diarrhea
 Unfavorable pH
 stomach acid, sweat, saliva, urine
 Lysozyme enzyme
 digests bacterial cell walls
 tears, sweat
AP Biology
2nd line: Non-specific patrolling cells
 Patrolling cells & proteins
bacteria

attack pathogens, but don’t
“remember” for next time
 leukocytes
 phagocytic white blood cells
 macrophages, neutrophils,
natural killer cells
AP Biology
macrophage
 complement system
 proteins that destroy cells
 inflammatory response
 stimulated by histamines
 increase in body temp.
 increase capillary permeability
 attract macrophages
yeast
Inflammatory response
AP Biology
*Initiated by release of histamines*
Fever
 When a local response is not enough

system-wide 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
AP Biology
of iron to grow
3rd line: Adaptive (active) Immunity
 Specific defense with memory
B cell

lymphocytes
 B cells - humoral response
 T cells – cell mediated response
 They respond to…

antigens
 cellular name tags
 specific pathogens
 specific toxins
 abnormal body cells (cancer)
AP Biology
B cells
 Involved in HUMORAL RESPONSE
 Attacks foreign antigens in blood or lymph
 Produce specific antibodies

against specific antigens
Types of B cells
 plasma cells
 immediate production of antibodies
 rapid response, short term release

memory cells
 continued circulation in body
 long term immunity
AP Biology
Humoral Immune Response
Helper T cells can activate B
cells directly.
AP Biology
What do antibodies do to invaders?
AP Biology
T cells
 Involved in CELL MEDIATED RESPONSE
 Attack, learn & remember pathogens hiding in
infected cells


recognize antigen fragments
also defend against “non-self” body cells
 cancer & transplant cells
 Types of T cells

helper T cells
 alerts rest of immune system

killer (cytotoxic) T cells
 attack infected body cells

memory T cells
 long term immunity
AP Biology
T cell attacking cancer cell
How do T cells know a cell is infected?
 Infected cells digest some pathogens

MHC proteins carry pieces to cell surface
 foreign antigens now on cell membrane
 called Antigen Presenting Cell (APC)
 macrophages can also serve as APC
 tested by Helper T cells
infected
cell
WANTED
MHC proteins displaying
foreign antigens
TH cell
T cell with
antigen receptors
AP Biology
Cell-Mediated Response
 Cytotoxic T cells
destroy infected body
cells or cancer cells
 activated by Helper T
 binds to MHC of APC
 secretes perforin
protein causing
apoptosis or lysis of
infected cell
 Creates memory
killer-T’s for further
exposures
AP Biology
Active Immunity
 Get exposed to pathogen!
Naturally – get sick
 Artificially – get a vaccination
 Both methods cause memory cells to be made for
future exposures.

Rapid response to
second exposure. You
don’t even know you
were exposed!
AP Biology
Passive immunity (antibodies not immune cells)
 Naturally
 obtaining antibodies from mother

antibodies pass from mother to baby across
placenta or in mother’s milk
 critical role of breastfeeding in infant health
 Artificially
injection of antibodies
 Ex: anti-venom serum
 short-term immunity

AP Biology
HIV & AIDS
 Human Immunodeficiency Virus

virus infects helper T cells
 AIDS: Acquired ImmunoDeficiency Syndrome

infections and death by opportunistic
diseases
 pneumonia, cancers
AP Biology
HIV infected T cell
AP Biology
Immune system malfunctions
 Auto-immune diseases

immune system attacks own molecules & cells
 rheumatoid arthritis
 Diabetes
 multiple sclerosis
 Allergies

makes wrong antibody for foreign antigen
 allergens = proteins on pollen, dust mites, in animal
saliva
 1st exposure you are not allergic. Allergy is confirmed
after subsequent exposures
AP Biology