Immunology Reviewer
Key Concepts
1.
Definitions
2.

Immunology: The study of the immune system and how it responds
to pathogens.

Immunogen: Any substance that can trigger an immune response.

Antigen: A substance recognized by the immune system (by B or T
cells) that may or may not provoke an immune response.

Epitope: The specific part of an antigen that is recognized by
immune cells.

Hapten: A small molecule that can only induce an immune response
when attached to a larger, immunogenic carrier.
3.
Properties of Antigens
4.

Foreignness: Antigens must be recognized as non-self by the
immune system.

Chemical Composition: Proteins are the most immunogenic; pure
lipids and nucleic acids are less so.

Molecular Size: Antigens larger than 10,000 daltons are more likely
to be immunogenic.

Stability: Antigens must remain stable in the body to elicit a
response.

Mode of Entry: The way an antigen is introduced (e.g., injection,
ingestion) affects the immune response.
5.
Immune System Overview
6.

Central Lymphoid Organs:

Bone Marrow: Site of B cell maturation.

Thymus: Site of T cell maturation.


Peripheral Lymphoid Organs:
Lymph Nodes, Spleen, MALT (e.g., tonsils, Peyer’s patches)
where immune responses occur.
7.
Types of Immunity
8.

Innate Immunity:


Non-specific, immediate response to pathogens.
Includes physical barriers (skin, mucous membranes) and
inflammatory responses.

Adaptive Immunity:

Specific response that develops after exposure to an antigen.

Involves B cells (produce antibodies) and T cells (kill infected
cells or help other immune cells).

Has memory, allowing for a faster response upon reexposure.
9.
Humoral vs. Cell-Mediated Immunity
10.

Humoral Immunity:

Involves antibodies produced by B cells.

Effective against extracellular pathogens (bacteria, viruses).

Cell-Mediated Immunity:

Involves T cells (CD4+ and CD8+).

Effective against intracellular pathogens (viruses) and
tumors.
11.
Immunoglobulins (Antibodies)
12.

IgG: Most abundant, crosses the placenta, involved in secondary
immune response.

IgM: First antibody produced, effective in primary response.

IgA: Found in secretions (saliva, tears), protects mucosal surfaces.

IgE: Involved in allergic reactions and defense against parasites.

IgD: Functions as a B cell receptor, no known antibody function.
13.
Primary vs. Secondary Immune Response
14.

Primary Response:

First exposure to an antigen; slower (7-10 days), produces
IgM and IgG.

Secondary Response:

Faster and stronger due to memory cells; primarily IgG.
15.
Hypersensitivity Reactions
16.

Type I: Immediate allergic reactions (e.g., pollen allergies); mediated
by IgE.

Type II: Antibody-mediated reactions (e.g., blood transfusion
reactions); involves IgG or IgM.

Type III: Immune complex-mediated reactions (e.g., serum sickness);
involves IgG or IgM.

Type IV: T cell-mediated reactions (e.g., contact dermatitis); involves
CD4+ and CD8+ T cells.
17.
Vaccines
18.

Purpose: Induce active or passive immunity to prevent diseases.

Types:

Live Attenuated: Weakened organisms (e.g., measles vaccine).

Inactivated: Killed organisms (e.g., polio vaccine).

Toxoid: Inactivated toxins (e.g., tetanus vaccine).

Subunit: Specific antigens (e.g., hepatitis B vaccine).

Mechanism: Stimulate the immune system to recognize and destroy
pathogens.
Summary

The immune system is essential for defending the body against infections.

It consists of various cells and proteins that work together to identify and
eliminate pathogens.

Understanding the differences between innate and adaptive immunity, as
well as the types of hypersensitivity reactions, is crucial for recognizing how the
body responds to infections and vaccines.
Are all antigens immunogens?
1.

No. Some antigens may not provoke a strong immune response on
their own (e.g., certain food proteins).

Vice versa: Not all immunogens are just simple antigens; they must
be capable of inducing a strong immune response.
2.
Are all immunogens antigens?
3.

Yes. Immunogens are a subset of antigens that specifically trigger
an immune response.

Vice versa: Not all antigens are immunogens because some may
not elicit a strong immune response.
4.
Are all antigens pathogens?
5.

No. Antigens can come from various sources, including nonpathogenic substances (like pollen or food).

Vice versa: Not all pathogens are antigens; some pathogens may
not present recognizable antigens to the immune system.
6.
Are all immunogens pathogens?
7.

No. Immunogens can be derived from non-pathogenic sources (like
vaccines made from inactivated viruses).

Vice versa: Not all pathogens are immunogens; some may not
provoke a strong immune response or may evade the immune system.
In summary:

Antigens: Can trigger an immune response (not always strong).

Immunogens: Always trigger a strong immune response.

Pathogens: Specifically cause disease (not all antigens or immunogens are
pathogens).

The human immune system is highly complex, second only to the brain.

It consists of numerous small organs and two large organs, with
a transport network throughout the body.

The immune system produces hundreds of billions of cells daily, organized
like an army.

It protects against microorganisms and cancerous cells.

A cut on the skin allows bacteria to invade.

Surviving cells release chemical signals to alert the immune system.

Macrophages are the first responders, attacking and consuming bacteria.

Neutrophils arrive to assist, causing collateral damage to surrounding cells.

Inflammation occurs as blood vessels allow fluid and complement
proteins to enter the area.

If initial defenses fail, dendritic cells collect samples of the invaders.

Dendritic cells seek out specific helper T cells to activate.

Helper T cells clone themselves to mount a stronger defense.

Activated helper T cells invigorate macrophages and activate B cells.

B cells produce antibodies that neutralize bacteria.

Memory cells remain after the battle for long-term immunity.

Historical Context: In 1796, Edward Jenner created the first vaccine using cowpox
material to protect against smallpox.


Vaccine Function: Vaccines prepare the immune system to recognize and combat
pathogens without causing the disease.


Immune Response:



Innate Defenses: Initial responses like coughing and inflammation.
Adaptive Immunity: Involves B and T cells that remember and target
specific invaders.

Types of Vaccines:


Live Attenuated: Weakened pathogens.

Inactivated: Killed pathogens.

Subunit: Specific parts of pathogens.

DNA Vaccines: Genes that produce antigens.

Future Prospects: Advancements in vaccine development may lead to effective
treatments for diseases like HIV, malaria, and Ebola.
