Immunity & Disease
1. Key Terms
● Immunity = “free from liability” (Latin origin). The immune system protects us from harmful
agents.
● Liability = something harmful to the body.
● Pathogens = disease-causing agents that enter from outside. Not all pathogens are living things.
● Disease = illness always caused by an external pathogen (e.g., COVID-19 infection).
● Disorder = illness caused internally (e.g., multiple sclerosis: immune system attacks myelin).
● Virulence = how easily/severely a pathogen causes disease. More virulent = more
hospitalizations.
● Antigen: traces pathogens leave behind
2. Types of Pathogens
Parasites (Worms/Helminths)
● Definition: Multicellular parasites, only animal pathogens.
● Examples: Roundworms, trichinosis, African eye worm.
● Notes:
○ Rare in developed countries.
○ Complex life cycle → move through body like “fugitives” to evade immunity.
Protozoa
● Definition: Single-celled, eukaryotic parasites.
● Examples: Malaria, Traveler’s diarrhea, giardiasis, African sleeping sickness.
● Notes:
○ Rare in developed countries; common in areas with poor sanitation.
○ Preventable with clean water and hygiene.
, ○ Present in water
Fungi
● Definition: Eukaryotic (have nucleus), can be single cells (yeast) or multicellular filaments
(mold).
● Examples: Ringworm, athlete’s foot, candidiasis, mushroom poisoning.
● Notes:
○ Less common than bacteria/viruses → fewer treatments available.
○ Major indirect impact: crop destruction → famine
○ Indirect effects in human health because they disrupt crop production
Prokaryote: Bacteria
● Definition: Prokaryotic, single-celled organisms (no nucleus).
● Examples: Strep throat, staph infections, tuberculosis, tetanus, syphilis, pneumonia.
● Treatment: Antibiotics → disrupt bacterial processes (cell wall, ribosomes, DNA replication).
● Antibiotic resistance:
○ Over-prescription → antibiotics given when unnecessary, exposing bacteria repeatedly.
○ Improper disposal → antibiotics flushed into environment, bacteria adapt.
○ Result: “superbugs” resistant to most drugs.
Viruses
● Definition: Strands of nucleic acid (DNA or RNA) wrapped in protein; need host cell to replicate.
● Mechanism: Hijack host machinery → make viral proteins/genomes → spread.
● Examples: Common cold, flu, measles, herpes, AIDS, COVID-19.
● Special points:
○ Can survive outside host for varying times (common cold up to 1 month).
○ Virulence vs persistence: viruses that survive long outside host often less virulent.
○ Vaccination: smallpox eradicated, COVID-19 controlled by vaccines.
Prions
● Definition: misfolded proteins that induce other proteins to also misfold
● Mechanism:
, ● Examples: creutzfeldt, mad cow disease, fatal familial insomnia
● Special points:
○ Resistant to standard sterilization. Eg. UV radiation
○ Difficult to get rid of and prevent
3. Immunity & Aging
● Pneumonia risk increases with age due to weakened immune systems.
● Cancer risk increases with age because immune surveillance weakens, abnormal cells escape
detection.
4. 🧬 Cancer & Immunity
● Causes of cancer (CaRRI + Viruses):
1. Carcinogens (chemicals agents that cause cancer cells to form, >120 known).
2. Radiation (UV, X-rays).
3. Repeated inflammation → DNA damage.
4. Inherited mutations (p53, Rb = intracellular tumor suppressors; RAS = intracellular
oncogene).
5. Viruses (e.g., HPV → cervical cancer).
● Three Phases of Cancer-Immune Interaction:
1. Elimination (Surveillance) → Immune cells destroy early tumor cells.
2. Equilibrium → Cancer mutates, immune system evolves, temporary balance.
3. Escape → Cancer evades detection → tumor growth, metastasis, symptoms.
● Incidence: Sharp rise in cancer after ~age 20.
5. Immune System Overview
● Innate: present from birth, fast, same response every time.
1. Key Terms
● Immunity = “free from liability” (Latin origin). The immune system protects us from harmful
agents.
● Liability = something harmful to the body.
● Pathogens = disease-causing agents that enter from outside. Not all pathogens are living things.
● Disease = illness always caused by an external pathogen (e.g., COVID-19 infection).
● Disorder = illness caused internally (e.g., multiple sclerosis: immune system attacks myelin).
● Virulence = how easily/severely a pathogen causes disease. More virulent = more
hospitalizations.
● Antigen: traces pathogens leave behind
2. Types of Pathogens
Parasites (Worms/Helminths)
● Definition: Multicellular parasites, only animal pathogens.
● Examples: Roundworms, trichinosis, African eye worm.
● Notes:
○ Rare in developed countries.
○ Complex life cycle → move through body like “fugitives” to evade immunity.
Protozoa
● Definition: Single-celled, eukaryotic parasites.
● Examples: Malaria, Traveler’s diarrhea, giardiasis, African sleeping sickness.
● Notes:
○ Rare in developed countries; common in areas with poor sanitation.
○ Preventable with clean water and hygiene.
, ○ Present in water
Fungi
● Definition: Eukaryotic (have nucleus), can be single cells (yeast) or multicellular filaments
(mold).
● Examples: Ringworm, athlete’s foot, candidiasis, mushroom poisoning.
● Notes:
○ Less common than bacteria/viruses → fewer treatments available.
○ Major indirect impact: crop destruction → famine
○ Indirect effects in human health because they disrupt crop production
Prokaryote: Bacteria
● Definition: Prokaryotic, single-celled organisms (no nucleus).
● Examples: Strep throat, staph infections, tuberculosis, tetanus, syphilis, pneumonia.
● Treatment: Antibiotics → disrupt bacterial processes (cell wall, ribosomes, DNA replication).
● Antibiotic resistance:
○ Over-prescription → antibiotics given when unnecessary, exposing bacteria repeatedly.
○ Improper disposal → antibiotics flushed into environment, bacteria adapt.
○ Result: “superbugs” resistant to most drugs.
Viruses
● Definition: Strands of nucleic acid (DNA or RNA) wrapped in protein; need host cell to replicate.
● Mechanism: Hijack host machinery → make viral proteins/genomes → spread.
● Examples: Common cold, flu, measles, herpes, AIDS, COVID-19.
● Special points:
○ Can survive outside host for varying times (common cold up to 1 month).
○ Virulence vs persistence: viruses that survive long outside host often less virulent.
○ Vaccination: smallpox eradicated, COVID-19 controlled by vaccines.
Prions
● Definition: misfolded proteins that induce other proteins to also misfold
● Mechanism:
, ● Examples: creutzfeldt, mad cow disease, fatal familial insomnia
● Special points:
○ Resistant to standard sterilization. Eg. UV radiation
○ Difficult to get rid of and prevent
3. Immunity & Aging
● Pneumonia risk increases with age due to weakened immune systems.
● Cancer risk increases with age because immune surveillance weakens, abnormal cells escape
detection.
4. 🧬 Cancer & Immunity
● Causes of cancer (CaRRI + Viruses):
1. Carcinogens (chemicals agents that cause cancer cells to form, >120 known).
2. Radiation (UV, X-rays).
3. Repeated inflammation → DNA damage.
4. Inherited mutations (p53, Rb = intracellular tumor suppressors; RAS = intracellular
oncogene).
5. Viruses (e.g., HPV → cervical cancer).
● Three Phases of Cancer-Immune Interaction:
1. Elimination (Surveillance) → Immune cells destroy early tumor cells.
2. Equilibrium → Cancer mutates, immune system evolves, temporary balance.
3. Escape → Cancer evades detection → tumor growth, metastasis, symptoms.
● Incidence: Sharp rise in cancer after ~age 20.
5. Immune System Overview
● Innate: present from birth, fast, same response every time.
