CLSC 2429 Unit 2 Chapter 12/13: Host Defenses

What are the three main goals a healthy immune system attempts to achieve?

Surveys the body.

Recognizes foreign material.

Destroys foreign entities.

What is innate immunity and what is its line of defense?

(Nonspecific): Includes the First Line (surface protection/anatomical/physiological barriers and Second Line (cellular/chemical system) of defense.

What is adaptive immunity and what is its line of defense?

(Specific): The Third Line of defense that must be developed uniquely for each microbe using specialized white blood cells.

How does the immune system differentiate self from non-self?

Antigens (markers) determine "self" vs. "non-self".

PRRs (Pattern Recognition Receptors) on host cells recognize PAMPs (Pathogen Associated Molecular Patterns) on foreign cells.

Define Hematopoiesis.

The process where all blood cells (WBCs, RBCs, platelets) originate from the hematopoietic stem cell in the bone marrow.

List the main Physical barriers.

Skin, mucous membranes, hair (nasal), vomiting, defecation, urination flow, sneezing.

List the main Chemical barriers.

Chemical: Lysozyme (in tears/saliva, breaks down bacterial cell walls), Acid pH (stomach HCl, vaginal secretions), and sweat.

Define lymph.

Plasma-like fluid that transports WBCs, cellular debris, and microbes.

How does lymph circulate?

Circulates one-way through lymphatic vessels, pumped by body movement.

What are primary lymphatic organs?

(Maturation): Bone Marrow (B-cell maturation; all cells start here) and Thymus (T-cell maturation).

What are secondary lymphatic organs?

(Response Site): Lymph nodes (filter lymph), Spleen (filters blood), and Associated Lymphoid Tissues (GALT, MALT, SALT).

What are the four components of the Second Line of Defense?

Phagocytosis, Inflammation, Fever, and Antimicrobial Products.

Define Phagocytosis.

Process of ingesting and eliminating foreign matter.

What are the cells involved in phagocytosis?

Neutrophils, Macrophages, and Dendritic cells.

List the key steps in Phagocytosis.

Chemotaxis (migration) → Adhesion (PRR binds PAMP) → Engulfment (forms phagosome) → Phagolysosome Formation (fusion with lysosome) → Destruction (via enzymes and reactive oxygen products) → Elimination (exocytosis of debris).

Define Diapedesis.

Migration of WBCs out of blood vessels into tissues.

Define chemotaxis.

Migration of cells (WBCs/phagocytes) in response to a chemical stimulus (chemokines) at the injury site.

What are the four steps (stages) of Inflammation?

Injury/Immediate Reactions (Vasoconstriction) → Vascular Reactions (Vasodilation, increased permeability, exudate/plasma seepage) → Edema and Pus Formation (Swelling, WBC/debris accumulation) → Resolution/Scar Formation (Tissue repair).

What are the effects/purpose of a Fever?

Inhibits multiplication of microbes, reduces iron availability for bacteria, increases host metabolism, and stimulates immune reactions/hematopoiesis.

Describe the action of Interferons (IFNs).

Small proteins produced by infected cells that warn nearby, uninfected cells. They cause nearby cells to synthesize antiviral proteins that block viral replication.

Describe Complement and its final result.

A cascade reaction destroying bacteria. The final stage is Membrane Attack, which forms puncture sites (pores) in the cell membrane, causing the cell to burst.

What are Antimicrobial Peptides?

Short, positive proteins that insert into and damage bacterial membranes. (defensin)

What are Restriction Factors?

Host molecules that limit viral replication by preventing viral synthesis, assembly, or release.