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Lecture 13 – Ch. 43: Immune System
I.
II.
Overview
Innate Immunity
A. components
B. cells
IIII. Adaptive/acquired immunity
A. Lymphocytes
i. B-cells
ii. T-cells
B. humoral vs. cell-mediated
immunity
C. Antibodies
D. MHC molecules
IV. Immune memory
V. Immune System Problems
VI. Preparation for next lecture
Thought Question:
Why do we not get sick EVERY time someone near us sneezes?
Overview
cilia of tracheal cells
Pathogens
Viruses
Bacteria
Macroparasites
Irritants
Pollen
Dust
dust
For example…
Virus
Bacteria
Macroparasites
Influenza
Strep
Malaria
Ebola
Black Plague
Sleeping Sickness
Chicken Pox
Salmonella
River Blindness
West Nile Virus
E. Coli
Elephantiasis
pollen
Overview
A Way In?
Skin breeches (cuts, punctures, scrapes)
Mucus membranes
Eyes
Nose
Mouth
Vagina
Urethra
Antigens =
foreign
molecules
specific to
the invader
Immunity Overview
Pathogens
(bacteria,
fungi, and viruses)
INNATE IMMUNITY
(all animals)
• Recognition of traits shared
by broad ranges of
pathogens, using a small
set of receptors
• Rapid response
ADAPTIVE IMMUNITY
(vertebrates only)
• Recognition of traits
specific to particular
pathogens, using a vast
array of receptors
• Slower response
Barrier defenses:
Skin
Mucous membranes
Secretions
Internal defenses:
Phagocytic cells
Natural killer cells
Antimicrobial proteins
Inflammatory response
Humoral response:
Antibodies in body fluids
Cell-mediated response:
Cytotoxic cells
disrupt pathogens.
Innate Immunity
External Barriers
Skin
Dry dead cells
Constantly sloughed off
Secretions
Contain natural antibiotics
Mucus physically traps microbes
Internal Barriers
Phagocytic cells – detect and engulf pathogens
Mast cells – cause inflammation and alert of damaged tissues
Innate Immunity
Leukocytes
Phagocytes - ingest foreign particles & cellular debris
Macrophages – consume many cells
Neutrophils – die upon consumption
Dendritic cells – stimulate adaptive immunity
Eosinophils – helpful against parasites, destructive enzymes
Dendritic cell
Natural killer cells
Attack cancerous or infected body cells
Use proteins & enzymes to lyse cells
Inflammation
Innate Immunity
Initiated by damaged or infected cells
Histamine release by mast cells
Capillary flow and permeability increased
Phagocytes drawn to area
Cytokines –
recruit more
lymphocytes
 leads to
pus, swelling,
redness, heat
Innate Immunity
Inflammatory “Symptoms”
Warm, red, painful
Result of leaky capillaries
Increased fluid secretions
Removal of dead cells and waste
Pain
Swelling, chemical response
Alerts injured organism
Leukocytes
and fluid = pus
NSAIDs
Innate Immunity
Antimicrobial peptides first discovered
in insects (like Drosophila).
Here, AMPs engineered to glow
green; upper fly infected by bacteria.
Antimicrobial peptides in vertebrates:
the complement – family of proteins,
activated by infection and lyse
infected cells
Interferons – chemicals made by
infected cells, trigger anti-viral
response
Adaptive Immune System
Acquired/ adaptive immunity –
lymphocytes made in bone
marrow  B cells and T cells
Antigen
receptors
mature in
bone marrow
mature in
thymus
Antibodies;
secreted or
embedded
in B cell
membrane
Cozy up to
infected
Mature B cell
cells, bind,
sometimes
lyse
Mature T cell
Responsible for circulating antibodies,
remembering pathogens, destroying infected cells
Adaptive Immune System
B cells
Humoral immunity
B cells & antibodies attack
pathogens before they
enter cells
After encounter pathogen,
B cells differentiate into
memory B cells and
antibody-producing cells
Each B cell produces
unique antibodies
Over 100 million different
antibodies in body 
chances of an antigen
encountering one that
fits are high
Antigen
receptor
Antibody
B cell
Antigen
Epitope
Pathogen
(a) B cell antigen receptors and antibodies
Antibody C
Antibody A
Antibody B
Antigen
(b) Antigen receptor specificity
Adaptive Immune System
Antibody action
Defend against pathogens in blood or fluid
Can inactivate pathogens by binding to epitopes
Can stimulate phagocytosis
Can neutralize toxins or block adhesion
Can trigger complement system where
blood proteins destroy invaders
Adaptive Immune System
T cells
Cell-mediated immunity
T cell receptors –
recognize pathogen
pieces ‘presented’
on infected cells
Displayed antigen
fragment
T cell
T cell
antigen
receptor
MHC
molecule
Antigen
fragment
Pathogen
Host cell
Cytotoxic T cells: Insert pores in infected cells,
enzymes break down cells
Helper T cells: stimulate B & cytotoxic T cell division
Some T cells develop into memory cells
Adaptive Immune System
Self-tolerance
MHC = major histocompatibility complex
All cells have MHC molecules – most body cells have MHC I
(lymphocytes have MHC II in addition)
MHC molecules displayed on cell surface – each binds a
specific peptide foreign fragment then “displays” it on surface.
Adaptive Immune System
Self-tolerance
T-cells (cytotoxic or helper T) bind to MHC presented antigens
Self-reactive lymphocytes with receptors to self epitopes are
eliminated before they leave bone marrow and mature
Adaptive Immune System
Humoral (antibody-mediated) immunity
Cell-mediated immunity
Key
Antigen (1st exposure)

Engulfed by
Antigenpresenting cell

Stimulates
Gives rise to


B cell
Helper T cell

Cytotoxic T cell

Memory
helper T cells



Antigen (2nd exposure)
Plasma cells
Memory B cells

Memory
cytotoxic T cells
Active
cytotoxic T cells
Secreted
antibodies
Defend against
extracellular pathogens
Defend against intracellular
pathogens and cancer
Adaptive Immune System
Immune system must remember past victories...
• Memory cells “remember” specific antigens
• May survive for years
• Respond faster and larger to repeat invasion
Adaptive Immune System
Memory
Memory B and T cells are able to recognize pathogens and
fight off infections immediately
Then why do you keep
catching a cold every year?
100+ rhinoviruses
Cold viruses can mutate
quickly
Vaccinations take advantage
of the immune response
Body is exposed to antigens to stimulate memory cells
Antibiotics
Antibiotics aid disease fight
Reduce growth and reproduction of living pathogens (not viruses)
Give immune system time to
fight infection
Humans have misused
antibiotics  “superbugs”
Overuse of antibacterial
products
Failure to complete full
course of antibiotics
Non-medicinal use of
antibiotics
Immune System Problems
Allergies
Immune overreaction
to harmless antigens
Histamine triggers
inflammation
Extreme response can
trigger anaphylaxis
Autoimmune Disorders
Immune system attacks healthy
body cells
Lupus, Rheumatoid Arthritis,
Multiple Sclerosis, Type 1
Diabetes, Celiac disease,
Crohn’s disease
Immune System Problems
Immune rejection
When tissue with “non-self” MHC
molecules contact immune system,
response mounted
Can be countered by
immunosuppressive drugs
Immune Deficiency Syndromes
Severe Combined Immune
Deficiency (SCID): Few/no immune
cells produced  genetic
Acquired Immune Deficiency
Syndrome (AIDS): Due to Human
Immunodeficiency Virus (HIV)
Destroys helper T cells
Thought Question:
What can you do to fortify your immune system?
Things To Do After Lecture 13…
Reading and Preparation:
1.
Re-read today’s lecture, highlight all vocabulary you do not
understand, and look up terms.
2.
Ch. 43 Self-Quiz: #1 – 7 (correct answers in back of book)
3.
Read chapter 43, focus on material covered in lecture (terms,
concepts, and figures!)
4.
Skim next lecture.
“HOMEWORK” (NOT COLLECTED – but things to think about for studying):
1. Compare and contrast: T cells and B cells, the humoral response
compared to the cell-mediated immune response.
2. Explain the function and parts of the human innate immune system.
3. Describe the problem with each of the following: allergies, autoimmune
disorders, immune deficiency syndromes.
4. Why are people concerned about over-use or misuse of antibiotics?