Immunity
• Nonspecific Defenses
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Surface barriers: skin, mucous membranes(lysozyme)
Phagocytic cells: WBC’s
Natural killer cells: perforins
Resident bacteria and fungi
Defensive proteins: interferons & complement
Fever
Inflammation: Redness, swelling, heat, pain
– Redness and heat from increased blood to
area
– Swelling from extra leaky capillaries
– Pain from chemicals released by cells
– Phagocytic cells arrive: clean up debris,
bacteria
• Specific Defenses - 2 parts
– Antibody immunity
– Cell-mediated immunity
– Antibody immunity involves 2 active components: 1.
the antigen and 2. the antibody
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Types of antigens –
The antibody – protein secreted by B lymphocytes
Structure of an antibody molecule/classes – IgG,IgM, etc.
Clonal selection – B cells
– Cell-mediated immunity – T cells – mature in thymus
• Macrophages (monocytes) engulf pathogen, digest it
• Parts of proteins “displayed”
• Presented to helper T cells with matching receptor – T cells
will form cytotoxic T cells or helper T cells.
• Action of antibody when encounters
antigen:
– Neutralization – viruses coated
– Agglutination – blood group antigens
• Immune response turned off by the
release of chemicals by suppressor T
cells; memory cells remain
Immunity and Vaccination
• Primary response takes time
• Secondary response quicker and stronger
• Vaccines artificially produce primary
response – killed or inactivated pathogens
• Immunity can last a few years, or decades
– “booster” shots
When things go wrong
• Autoimmune disorders – failure to
recognize “self” markers
– Lupus, multiple sclerosis, rheumatoid arthritis,
Type 1 diabetes, etc.
• Allergies
– Overreaction to pollen, food, insect stings
– Mast cells & basophils release histamine
• Anaphylactic shock – allergen has entered
the blood stream
Acquired Immune Deficiency
Syndrome
• Caused by HIV infection (human
immunodeficiency virus)
• Targets helper T cells
• Cripples entire immune system
• Death from opportunistic infections
• Thought to have originated in Africa
• Virus structure
– RNA genome (retrovirus)
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Protein coat
Phospholipid envelope
Glycoprotein spikes – gp120
Reverse transcriptase enzyme
• Life Cycle
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gp120 binds to CD4 receptors
Viral envelope fuses with cell membrane
Reverse transcriptase copies RNA to DNA
DNA inserts into cell chromosome (latency)
Later, activation produces viral RNA and protein
• Transmission
– Sexual contact without latex condom
– Intravenous drug use
– Blood transfusion
– Mother to fetus – crosses placenta
• Testing
– Typically look for antibodies in blood (HIV +)
– Can also look for viral proteins or RNA
• Stages of Infection
– Initial infection (flu like symptoms)
– Asymptomatic stage: multiplies in lymph
nodes
– Eventually, AIDS
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Low helper T count (under 200/cc)
Opportunistic infections occur
Loss of 10% body weight
Dementia
Death results as body weakens and infections
accumulate
• Opportunistic infections
– Fungal: thrush, Pneumocyctis carinii in lungs,
others
– Protozoa, bacteria
– Cytomegalovirus
– Cancers: Kaposi’s sarcoma, lymphoma
• Treatments
– Drugs: reverse transcriptase inhibitors (AZT),
protease inhibitors, “cocktail” combination
– Side effects, viral resistance
– Vaccine???? – High mutation rate of HIV;
latent infections