Immune System
Immune System Overview
Influenza Infection
phagocytic
leukocyte
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Immune Systems
 Highly developed in

mammals
Two types of
immunity:
1.
2.
Innate immunity
(nonspecific)
Acquired
immunity
(specific)
What about other organisms?
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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, acquired immunity
 “elite trained units”

lymphocytes & antibodies
 B cells & T cells
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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
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2nd line: Non-specific patrolling cells
 attack pathogens, but don’t
bacteria
“remember” for next time

leukocytes
 phagocytic white blood cells
 macrophages, neutrophils,
natural killer cells, dendritic cells

Antimicrobial proteins
macrophage
 Complement system
 Interferons

inflammatory response
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 increase in body temp.
 increase capillary permeability
 attract macrophages/neutrophils
yeast
Inflammatory response
Histamine and cytokines increase
blood flow to damaged site, making
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it
look red and puffy = INFLAMMED!
3rd line: Acquired (active) Immunity
 Specific defense with memory
B cell

lymphocytes
 B cells - humoral response
 T cells – cell mediated response
 They respond to…
Antigens!

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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
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How are invaders recognized?
 Antigens - cellular name tag proteins
 “self” antigens
 no response from WBCs
 Major Histocompatibility Complex – MHC

Protein used by all cells for recognition
 “foreign” antigens
Mature
 response from WBCs
lymphocytes are
 pathogens: viruses, bacteria, protozoa, parasitic worms,
tested to make
sure they can
distinguish self
vs. non-self
“self”
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fungi, toxins
 non-pathogens: cancer cells, transplanted tissue, pollen
“foreign”
Humoral Immune Response
 In the diagram above a B cell is being activated by a
T helper cell. This B cell will make plasma cells and
memory B cells that will secrete antibodies to fight
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Biology
the
current and future infections.
What do antibodies do to invaders?
Antibodies in Action
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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

cytotoxic (killer) T cells
 attack infected body cells

memory T cells
 long term immunity
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T cell attacking cancer cell
How do T cells know a cell is infected?
 Infected cells digest some pathogens

Class I MHC proteins carry pieces of foreign
cell to surface
 foreign antigens now on cell membrane
 called Antigen Presenting Cell (APC)
 Helper T cell becomes active
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Cell-Mediated Response
 Activation of Helper T cell results in activation of


Cytotoxic T cells (as well as B cells)
Cytotoxic T cells destroy infected body cells or
cancer cells (look for Class I MHC)
Cytotoxic (killer) T cells secrete perforin protein
causing apoptosis or lysis of infected cell
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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!
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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

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HIV & AIDS
 Human Immunodeficiency Virus

virus infects helper T cells
 AIDS: Acquired ImmunoDeficiency Syndrome

infections and death by opportunistic
diseases
 pneumonia, cancers
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HIV infected T cell
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
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