Transcript Immune System

Immune System
Chapter 16
Immune system
• Immunity- the body’s ability to protect itself from
disease-causing entities (pathogens)
Immune system functions
• Recognize/remove abnormal “self” cells
– Abnormal cell growth and development
• Removes dead/damaged cells
– e.g., old red blood cells
• Protects from pathogens (disease causing
invaders)
– Any exogenous molecule/cell
Immune cells
• Leukocytes (white blood cells)
• Most circulate in blood but leave and function
extravascularly
• Some live in tissues
Immune response
• Two categories
– Innate (nonspecific)
– Acquired
Innate immunity
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Present from birth
Nonspecific immune response
Quick
Immune cells are genetically programmed to
respond to a broad range of foreign material
• Either clears infection or contains it
Innate immunity
– Physical barriers
(first line of
defense)
– Chemical
Innate immunity
• If pathogens get past physical/chemical
barrier, immune cells respond
• Natural killer (NK) cells
• Phagocytes
Innate immunity
• Inflammation
– Immune cells release cytokines
– Cytokines attract other immune cells and increase
capillary permeability
– Benefits:
• Attracts immune cells to site
• Produces physical barrier
Innate immunity
• Fever
– Stimulates immune cell proliferation
– Elevated body temp has indirect effect on
microbes
Acquired (adaptive) immunity
• Third line of defense
• Distinguishes self from non-self
• Targets specific antigens
• Substance that stimulates immune response
• Typically on surface of cells
Acquired immunity
• Mediated primarily by lymphocytes
• T lymphocytes
– Cells that attack and destroy virus-infected cells
(killer T)
– Cells that direct other immune cells (helper T)
• B lymphocytes- develop into plasma cells that
secrete antibodies
Killer T
• Release cytotoxins to destroy infected cells
Helper T cells
• Produces proteins to activate killer T cells and
B cells
B cells
• Group of lymphocytes specific to one antigen
• Determined by receptor
• Only a few of each clone, unless pathogen
enters, then they reproduce
Antibodies
• Protein that detects
pathogens
• Produced by plasma cells
• Free antibodies bind to
antigens and signal to
immune cells to destroy
Acquired immunity
• Repeated exposures, increased number of
cells with memory, allows for more rapid
reaction
Acquired immunity
• Two categories
– Active immunity- exposure to pathogen, body
produces its own antibodies (natural or artificial)
– Passive immunity- acquisition of antibodies made
by another organism (natural or artificial)
Artificially acquired active immunity- Vaccines
• Expose individual to live
or killed pathogen to
stimulate antibody
production and antigen
memory
Pathogens
• Viral- infectious agent that
replicates only inside the living
cells of other organisms
• Bacterial- free living, single
celled, group of
microorganisms
• Parasites- lives in/on a host
and gets its food from/at
expense of host
Viral life cycle
• Take over of a host’s cell
Immune system pathologies
• Incorrect responses
– Failure to distinguish self from non-self,
autoimmune disease
• Overactive responses
– Response out of proportion to threat, allergies
• Lack of response
– AIDS
Incorrect response
• Failure of an organism in recognizing self
• Immune response against its own cells/tissues
• Autoimmune disease
– Can be triggered by an infection (foreign antigens
that are similar to human antigens)
Autoimmune diseases
• Celiac disease
• Gluten is modified by an enzyme in the small
intestines
• The immune system attacks gluten at the
epithelial cells of the bowels
• Causes damage to the villi, which interferes
with nutrient absorption
Autoimmune diseases
• Multiple sclerosis
• T cells recognize myelin as foreign and attacks
• Release of cytokines attracts other immune
cells, inflammation
Overactive response
• Allergic reactions
• Same process as regular immune reaction
• Can be from almost anything (organic,
inorganic, natural, synthetic)
• Appears to have a genetic basis
Lack of response
• One or more components of the immune
system are inactive
• E.g., Immune system fails to recognize
intruders
• E.g., Immune system can’t keep up with
intruder mutations
Human Immunodeficiency Virus (HIV)
• Transmission- bodily fluids in contact with mucous
membranes
• Viral infection that attacks helper T cells
• Interruption of helper T activity means no
communication with B and killer T cells
• Allows for opportunistic infection
HIV
• Virus replicates, eventually induces death of T
cell host
• Viral load increases in the body
• Fewer T cells, stresses immune system
HIV/AIDS
• Primary infection- HIV destroys T cells
• Latent infection- decline of production of T cells
• Acquired immunodeficiency syndrome (AIDS)- T cell count less
than 200
AIDS
• Body can’t fight off other opportunistic
infections
• People die from secondary infections, rather
than from the virus itself
Secondary infections
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Candidiasis
Cancer (Kaposi’s sarcoma)
Pneumonia
Many others
• Cryptococcal Infection
HIV treatment
• Mutation rate is high, new strain every two
days, drugs don’t recognize new strains
• Virus can become immune, especially to single
drug treatments
• Patients typically given a cocktail of drugs