11 Biology - Immune System

Pathogenesis

Is the biological mechanism through which a pathogen causes disease in a host organism

• involves entering the host and evading the immune system, colonising tissues and damaging host cells or tissues.

Adherence Factors

Is the first step after exposure to a pathogen, allowing it to attach to host cells and resist physical removal and begin colonisation

Mechanisms of Adherence

Fimbriae / Pili: hair-like appendages that aloow bacteria to attach to specific receptor sites on host cells.

Adhesions: surface proteins that help it stick

Invasion Factors

Once adhered, pathogens need to invade deeper tissues to spread and access nutrients.

Capsules

Capsules help bacteria evade immune detection and prevent phagocytosis (cell eating)

Immune Evasion Strategies

• Prevents antibody binding: antibodies cannot easily attach to the capsule, so phagocytes aren’t alerted.

• Inhibits phagocytosis: Immune cells can’t grip or engulf the slippery capsule.

• Mimics host molecules: Some capsules resemble human tissue components such as developing a certain glycoprotein which signals other cells into thinking it is a human cell.

Exotoxins

Produced inside the cells and secreted into tissues.

• made of proteins.

Endotoxins

Found outside the cells released only when the bacteria die.

3 types of Disease Transmissions

1. Contact

2. Vehicle

3. Vector

Contact Transmission

1. Droplet Transmission - droplets discharged into the air

2. Direct Contact - direct contact between its source and potential host

3. Indirect Contact - includes touching contaminated surfaces

Vehicle Transmissions

Disease may be transmitted through a medium / substance like water, food and blood.

Vector Transmission

Spread of diseases through organisms, such as insects or ticks, that carry pathogens from one host to another.

Types of Vehicle Transmission

1. Waterborne diseases

2. Foodborne diseases

3. Bloodborne diseases

Line of Defence

Immune system’s protect

First Line of Defence

Physical and Chemical barriers to the entry of pathogens

Second Line of Defence

Innate Immunity

Adaptive Immunity

Adaptive immunity - learning process comes with time.

Prostaglandins

Damaged cells release prostaglandins which is a chemical that directs blood flow to an injured area.

• these chemicals attract phagocytes that eat germs and dead / damaged cells.

Phagocytes

White blood cells that engulf and digest pathogens and dead cells, helping clear infections and initiating tissue repair.

MHC - Major Histocompatibility Complex

Proteins located on the surface of a cell which help identify difference between host cell and virus cell

Histamine

Histamines cause vasodilation which aids in increasing blood flow to the affected area.

White blood cells

Leukocytes

Types of White blood cells

• Basophils and Mast cells

• Neutrophils

• Monocytes

• Lymphocytes

• Eosinophils

Basophil and mast cells

Chemokines released when pathogens enter the body which stimulates basophils and mast cells to release histamines.

Neutrophils and Monocytes

Phagocytes that ingest foreign matter

• when neutrophils die, they produce pus.

Neutrophils live short amount of time compared to monocytes

Eosinophil

A white blood cell that is involved in the break down of microparasites or in allergic reactions.