Immunology and Disease: Key Concepts, Defense Mechanisms, and Immune Responses

Key Terms and Concepts:

• Disease: Condition that impairs body function.

Epidemiology:

Study of disease in hosts populations

• Reservoir: Source of infection (animal, human, environment).

• Pathogenicity: Ability to cause disease.

• Virulence: Degree of pathogenicity.

• ID50: Dose needed to infect 50% of hosts.

• Transmission: Direct, indirect, vector-borne.

• Vector Types: Biological (mosquito) vs mechanical (fly).

• Endemic: Constantly present.

• Epidemic: Sudden rise.

• Pandemic: Global spread.

• Nosocomial: Hospital-acquired infection.

• Typhoid Mary: Example of asymptomatic carrier.

Lymph system

Network that transports lymph and supports immune cell circulation

• Leukocytes (white blood cells):

Defend the body against infections and foreign invaders.

• Neutrophils:

Most abundant phagocytic cells; first responders to infection.

• Eosinophils:

Attack parasites and modulate allergic responses.

• Basophils:

Release histamine during inflammation and allergic reactions.

• Macrophages:

Engulf pathogens and present antigens to T cells.

• Lymphocytes:

Include B and T cells that coordinate immune responses.

• Lysozyme:

Enzyme in tears/saliva that breaks down bacterial cell walls.

• Mucociliary escalator:

Moves trapped microbes out of respiratory tract.

• Interferon:

Proteins released by virus-infected cells that block viral replication.

• Complement system:

Series of proteins that enhance immune responses by lysis and opsonization.

• PAMPs:

Pathogen-associated molecular patterns; recognized by immune cells.

• PRRs:

Pathogen recognition receptors (like Toll-like receptors) that detect PAMPs.

• Cytokines:

Signaling molecules coordinating immune activity.

• Chemotaxis:

Movement of immune cells toward infection site.

• Inflammation:

Localized response to infection or injury.

• Phagocytosis:

Engulfing and digesting microbes.

• Opsonization:

Coating pathogens to enhance phagocytosis.

1. Lines of Defense: - First line:

Physical and chemical barriers (skin, mucous membranes,

secretions).

- Second line:

Innate immune responses (phagocytes, inflammation, fever, complement).

- Third line:

Adaptive (specific) immunity involving lymphocytes and antibodies.

First Line Factors:

Skin, mucous membranes, tears (lysozyme), stomach acid, and normal flora.

3. Inflammatory Response:

Vasodilation, increased permeability, phagocyte migration, tissue repair.

4. Phagocytic Cells:

Neutrophils, macrophages, dendritic cells; they engulf pathogens and present antigens

5. Interferons:

Released by infected cells; signal nearby cells to produce antiviral proteins.

6. Complement System:

A group of proteins that enhance immune responses by lysis of microbes and opsonization.

7. PAMPs and PRRs:

PAMPs are microbial patterns (like LPS); PRRs (like TLRs) recognize them to trigger innate defense.

Specificity & Memory:

Immune system targets specific antigens and "remembers" them for faster secondary responses.

2. Antibody Diversity:

Generated by gene rearrangements in B cells.

3. B vs T Lymphocytes:

B cells make antibodies (humoral); T cells manage cellular immunity.

4. Clonal Selection:

Activation and proliferation of lymphocytes with receptors matching an antigen.

5. Memory Cells:

Long-lived cells that respond quickly to future infections.

6. Primary vs Secondary Response:

Primary is slow; secondary is faster due to memory cells.

7. Antibody Structure:

Y-shaped; two heavy and two light chains with variable antigen-binding regions

8. Antigen-Presenting Cells (APCs):

Macrophages, dendritic cells, and B cells that display antigens with MHC molecules.

Types of Immunity: Natural active

Infection.

Types of Immunity: Natural passive

Maternal antibodies.

Types of Immunity: Artificial active

Vaccination.

Types of Immunity: Artificial passive

Patient receives immune serum from another donor

Types of Immunity: Herd Immunity

Population-level protection due to widespread immunity.

- Inactivated:

Safe, may need boosters.

- Attenuated:

Strong, long-lasting, but risky for immunocompromised.

- Subunit:

Uses parts of microbe (safe but may need adjuvants).

4. Immunological Tests:

can test for the presence of antibody or antigen

5. Monoclonal Antibodies:

Produced by hybridomas; uniform and specific; useful in diagnostics and therapy

• Disease:

Condition that impairs body function.

• Epidemiology:

Study of disease occurrence and spread.

• Reservoir:

Source of infection (animal, human, environment).

• Pathogenicity:

Ability to cause disease.

• Virulence:

Degree of pathogenicity.

• ID50:

Dose needed to infect 50% of hosts.

• Transmission:

Direct, indirect, vector-borne.

• Vector Types:

Biological (mosquito) vs mechanical (fly).

• Endemic:

Constantly present.

• Epidemic:

Sudden rise.

• Pandemic:

Global spread.

• Nosocomial:

Hospital-acquired infection.

• Typhoid Mary:

Example of asymptomatic carrier