The Immune System and Pathogens

Purpose of Immune System

• Protects the body from disease by destroying foreign substances like pathogens.
• Maintains overall health.

Pathogens

• Include fungi, parasites, viruses, and bacteria.
• Virulence refers to the severity of a disease's symptoms.
• R naught (R0) is the average number of people an infected person will spread a disease to.

Fungi

• Obtain nutrients from our cells and/or release toxins.
• Some cause disease, such as athlete’s foot.
• Transmitted by touching infected surfaces of skin.
• Can be treated with antifungal medication.

Viruses

• Attack only one type of cell.
• Smallest form of pathogen.
• Consists of genetic material wrapped in a protein coat (capsid).
• Most are pathogenic.
• Not living (no cells).
• Some are beneficial.
• Some are zoonotic.
• Can have an outer lipid envelope.
• Requires a host cell to reproduce.
• Attaches to a cell's surface using proteins on its capsid or envelope.
• Tricks the cell into internalizing it through endocytosis.
• Replicates inside the cell, potentially killing, damaging, or changing the infected cell.
• Leaves the cell to infect more cells.

Bacteria

• Unicellular prokaryotes.
• Obtain nutrients from our cells and/or release toxins.
• Asexually reproduce through binary fission.

Binary Fission

• Exponential growth occurs.
• DNA (plasmids + DNA strand) is copied.
• Strands of DNA move to opposite sides of the cell.
• Grows a new cell wall down the middle, allowing it to pull apart.
• Plasmids are arranged randomly.

Binary Fission Math

• To calculate the number of bacteria after a certain time, use the formula (2)^n, where n is the number of division cycles.
• Example: If bacteria divide every 30 minutes, after 3 hours (180 minutes), there will be 6 cycles of division (180/30 = 6).
• Result: (2)^6 = 64 bacteria.

Parasites

• Steal nutrients or eat cells.
• Examples: Hookworm and tapeworm.

Spread of Pathogens

• Infectious diseases spread through various methods.
• Direct Contact: Close contact between people spreads diseases like HIV/AIDS, Hepatitis B, and Herpes.
• Contamination (water): Bacteria is spread by contaminated water, like cholera.
• Airborne: Tiny droplets released into the air when someone sneezes or coughs, spreading viruses like measles, tuberculosis, chickenpox, common cold, and flu.
• Indirect Contact: Contact with a contaminated substance or item (e.g., needles), spreading ringworm.
• Vectors: Living organisms transmit pathogens to humans (e.g., blood-sucking insects), spreading diseases like malaria and Lyme disease.

Factors Increasing Disease Spread

• Increased global travel.
• Poverty and limited access to safe food & water.
• High population density.
• Population mixing.
• Limited good hygiene practices.

Avoiding Illness

• Wash hands with soap for 20 seconds after using the bathroom or touching dirty surfaces.
• Sneeze and cough into elbow.
• Get all recommended vaccines every year.

Zoonotic

• When a virus jumps from an animal to a human, it mutates to bind to receptors in human cells.

Immune System Protection/Function

• Includes multiple lines of defense.

First Line of Defense

• Physical Barriers: Skin, mucus membranes, and cornea.
• Tears, sweat, and saliva help.

Second Line of Defense

• Non-specific WBCs called macrophages engulf pathogens through phagocytosis.
• Macrophages break down pathogens by mixing them with enzymes stored in lysosomes, which is part of the inflammatory response.

Third Line of Defense

• Specific Defence = Adaptive Immune Response.
• Targets specific pathogens previously encountered.
• Leukocytes (WBCs): Lymphocytes (B and T cells), Phagocytes (Macrophages).
• B cells have receptors on their surface that recognize specific antigens on pathogens and mark them with antibodies (proteins) for destruction by T cells.
• Some B cells become memory cells.
• WBCs (B&T) work together to destroy the pathogen, causing clumping, symptoms, or death.

Stem Cells

• Unspecialized cells that produce other specialized cells (like WBC) in bone marrow.

Foreign Materials

• Allergens, pathogens, and organ transplants.

Allergies

• WBCs identify harmless substances as foreign and produce antibodies/attack them, leading to symptoms.

Immune System Organs + Tissues

Lymph Nodes

• Glands throughout the body filter bacteria and viruses, which are then destroyed by WBCs.

Spleen

• Filters blood and provides storage for platelets and WBCs.

Thymus

• T cells mature into cells that fight disease.

Bone Marrow (Stem cells)

• Contains stem cells that mature into WBCs, RBCs, and platelets.

Appendix

• Unknown: Theory = storage site of good bacteria

Vaccines

• Expose the body to a dead or weakened form of a pathogen, causing mild symptoms.
• The body launches an immune system response, producing antibodies.
• When encountering the real pathogen, the body has already familiarized itself, resulting in immunity.
• The body attacks the real pathogen more quickly and efficiently.
• Some people can’t receive vaccines due to being immunocompromised, being a newborn or being pregnant.

Herd Immunity

• When enough people are vaccinated, outbreaks are so low that even those who aren’t immunized benefit.

Boosters

• Over time, the number of antibodies in the body can decrease, reducing immunity.
• Some viruses mutate over time, changing their antigens so our antibodies no longer recognize them.
• Booster shots remind the immune system of the pathogen, leading to a stronger and faster response if exposed again.

Antibiotics

• Target bacteria, causing them to die or preventing them from reproducing.
• Interfere with cell wall formation, leading to cell death.
• Mutated cells take over while other cells die with antibiotics.
• When taking antibiotics, probiotics like yogurt and kimchi should be consumed to replenish good bacteria.

Natural Selection- An organism

• An organism with traits better suited to its environment are more likely to survive & reproduce, passing on those advantageous traits to their offspring, leading to gradual population change over time.

Mutations

• During binary fission, bacteria make a copy of their DNA, increasing the chance for mutations.
• Bacteria compete for resources, and some mutations give them the ability to produce their own antibodies and kill good bacteria.

Bacteria Competition + Mutation:

• Compete for resources in environment.
• Some mutations give bacteria the ability to produce their own antibodies & kill good bacteria.
• Reproduce, pass trait

Antibiotics side effects

• Antibiotics are not always needed due to side effects and the risk of antibiotic resistance.
• Antibiotics can give mutated bacteria an advantage by eliminating regular bacteria and allowing only mutations to multiply.
• This can lead to more mutations and increased antibiotic resistance.

Organ Transplants

• Replacement of a damaged or missing organ from a healthy donor with the same blood type.
• Risky because the body may recognize the transplanted organ as foreign.
• Immune response: The immune system attacks the organ, leading to organ rejection.
• Immunosuppressants suppress the immune system to avoid organ rejection.
• Benefits: No organ rejection.
• Risks: Weakened immune system.

Overview of the immune system's role in protecting the body from pathogens such as fungi and viruses. Includes the characteristics, transmission, and treatment of these pathogens, as well as concepts like virulence and R naught.