Topic 25- Adaptive Immunity

What is the difference between active and passive immunity?

Active = body produces its own immune response; Passive = immunity borrowed (e.g., antibodies from another source).

What are the types of immunity based on how they are acquired?

Natural (through infection or maternal antibodies) and Artificial (via vaccination or antibody injection).

How long does it typically take adaptive immunity to respond fully?

Around 28 days.

What type of white blood cells are central to adaptive immunity?

Lymphocytes (B cells and T cells).

Where do B cells and T cells originate and mature?

Originate: Bone marrow; Mature: B cells – bone marrow, T cells – thymus.

What is an antigen?

A foreign substance that triggers an immune response; often a protein or polysaccharide.

What is an epitope?

The specific part of an antigen that binds to a receptor on B or T cells.

What is an antibody (immunoglobulin)?

A protein produced by B cells that binds to specific antigens.

How diverse are B and T cell receptors?

Over 1 million B-cell types; over 10 million T-cell types.

What does self-tolerance mean?

The immune system can distinguish self from non-self to avoid attacking the body’s own cells.

What is immunological memory?

The ability of the immune system to respond more quickly to pathogens it has encountered before.

What is the difference between a primary and secondary immune response?

Primary: slower (10–17 days); Secondary: faster (2–7 days), stronger, more efficient.

What happens during clonal selection?

Activated B/T cells divide into effector cells (to fight) and memory cells (for future response).

What shape are B-cell receptors and what do they bind?

Y-shaped; bind directly to free antigens.

What do B cells produce upon activation?

Antibodies (immunoglobulins).

What kind of pathogens do B cells respond to?

Extracellular pathogens (e.g., in blood or lymph).

Do T cells produce antibodies?

No, they recognize antigen fragments and directly kill infected cells or help other cells.

compare and contrast key terms

Term	Definition	Compare With	Key Differences
Antigen	A foreign molecule that triggers an immune response	Epitope	Epitope is a specific part of an antigen
Antibody (Ig)	Protein made by B cells that binds to antigens	Antigen	Antibody is made in response to antigen
Epitope	Specific region on an antigen recognized by receptors	Antigen	Epitope is the part that binds to immune receptors
Passive Immunity	Borrowed antibodies (e.g., injection or maternal)	Active Immunity	Passive is temporary and externally sourced
Natural Immunity	Acquired via infection or maternal antibodies	Artificial Immunity	Artificial immunity is induced by vaccines

Compare and Contrast Characteristics of Adaptive Immunity

Characteristic	Adaptive Immunity	Innate Immunity	Difference
Specificity	Highly specific to antigens	General, broad pattern recognition	Adaptive targets specific invaders
Memory	Long-term memory present	No memory	Adaptive “remembers” previous infections
Response Time	Slow (days)	Fast (minutes–hours)	Innate is immediate; adaptive takes longer
Diversity	Millions of receptors	Limited receptor types	Adaptive recognizes more pathogens
Self-Tolerance	Yes	Partially	Adaptive trained to avoid attacking self

Compare and Contrast B and T Cells

Feature	B Cells	T Cells
Maturation Site	Bone marrow	Thymus
Target	Pathogens in fluids	Infected cells
Receptor Shape	Y-shaped	Linear receptor
Antigen Recognition	Direct binding	Needs antigen presentation (MHC)
Secretes	Antibodies	Cytokines or cytotoxic proteins
Main Subtypes	Plasma cells, Memory B cells	Helper T cells, Cytotoxic T cells

Sequence B and T Cell Function

B Cell Function:

1. Detects and binds to antigen in fluid

2. Activates (with or without T cell help)

3. Clonal expansion

4. Differentiates into plasma and memory B cells

5. Plasma cells produce antibodies

T Cell Function:

1. APC presents antigen on MHC

2. T cell binds to antigen-MHC complex

3. Helper T cells activate via cytokines

4. Cytotoxic T cells destroy infected cells

5. Both generate memory T cells

Hypothesize and Diagnose the Impact of Variability on B & T Cells

Scenario	Possible Outcome
Low receptor diversity	Fewer pathogens recognized → poor immune coverage
Loss of self-tolerance	Autoimmune response → attacks own body
Failure of clonal expansion	Weak immune response → insufficient effector cells
No memory cell formation	Re-infection leads to full response again → no fast recovery

Compare and Contrast Responses to Antigens

Feature	Cell-Mediated Response	Humoral Response
Involved Cells	Cytotoxic T cells	B cells and antibodies
Target	Infected cells	Pathogens in blood/fluids
Trigger	Antigen presented on MHC I	Antigen binds to B cell receptor
Mechanism	Perforin and granzymes kill cells	Antibodies neutralize and opsonize
End Result	Infected cells destroyed	Pathogens neutralized or phagocytosed

Sequence Responses to Antigens

• Pathogen enters body

• APC engulfs and presents antigen

• Helper T cell binds to presented antigen

• Helper T cell secretes cytokines

• Cytokines activate B cells and cytotoxic T cells

• B cells produce antibodies

• Cytotoxic T cells kill infected cells

• Memory cells are created

Hypothesize and Diagnose the Impact of Variability on Responses to Antigens

Change or Defect	Predicted Impact
APC fails to present antigen	No T cell activation → entire adaptive response compromised
No cytokine production by Helper T cells	No activation of B cells or cytotoxic T cells
Mutation in antigen structure	Immune evasion → no recognition by immune cells
Failure to produce antibodies	Poor humoral response → extracellular pathogens persist

Sequence Vaccine Activity

1. Vaccine (antigen or genetic material) is introduced into the body

2. APCs take up the material and present the antigen

3. Helper T cells recognize and bind to the presented antigen

4. Helper T cells release cytokines

5. Cytokines activate B cells and cytotoxic T cells

6. B cells produce antibodies; cytotoxic T cells prepare for response

7. Memory B and T cells form

8. Future exposures trigger rapid secondary response