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

Polio

Viral; causes paralysis and is often permanent

• 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

Measels

Virus; leading causes of death in children

Rubella

Virus; infection during miscarriage - include cataracts, deafness, heart and brain

Mumps

Viral; Pancreatitis, deafness, infertility

Whopping Cough

Bacterial; children less than a yr old may have little or no cough and instead have periods where they don’t breathe

Diphtheria

Bacterium; myocarditis, inflammation of nerves, kidney issues and bleeding can result in paralysis

Smallpox

Virus; mortality rate 30-35%

Phagocytic cells

Neutrophils, macrophages, monocytes, dendritic cells, and eosinophils.

Importance to innate immunity

PRRs recognize PAMPs to quickly trigger the innate immune response against invaders.

Live vaccine

Contains a living but weakened (attenuated) form of the pathogen.

Attenuated vaccine

A weakened form of the pathogen that can’t cause disease but triggers immunity.

Subunit vaccine

Contains only parts (antigens) of the pathogen, not the whole organism.

DNA vaccine

Uses DNA that codes for an antigen to trigger an immune response.

Fluorescent antibody test

Uses fluorescent dye–tagged antibodies to detect specific antigens or cells.

Agglutination test

Detects antigens or antibodies by visible clumping of particles.

ELISA test

Detects and measures antibodies or antigens using enzyme-linked reactions.

Serological test

Uses blood serum to detect antibodies or antigens.

Precipitation test

Detects soluble antigens and antibodies by forming a visible precipitate.

Monoclonal antibody

Identical antibodies made from one B-cell clone that target a single antigen.

Antiserum (polyclonal antibody)

Serum with a mixture of antibodies against different parts of an antigen.

Lateral flow immunoassay

Simple strip test (like a COVID or pregnancy test) that detects antigens or antibodies.