11.1.410-11 · Infectious Disease and Immunity

Memory Cells and Immunity — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

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📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision

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11.1.4 Memory Cells and Immunity — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Explain how memory cells give a faster, larger secondary response and long-term immunity.Formation — during clonal expansion in the primary response, some B cells and T cells become mem…

Recognition
Antibody timing
Antibody level
First curve
Second curve
Explanation

Part 1 of 8Memory cells

Formation

Formation during clonal expansion in the primary response, some B cells and T cells become memory cells instead of effector cells.

Life span

Life span they are long-lived, sometimes for decades, and circulate in blood and lymph and stay in lymph nodes.

Receptors

Receptors they have the same specific receptors as the selected cell.

Numbers

Numbers after the infection they remain at a higher number than the original naive lymphocytes of that specificity.

Result

Result this gives immunological memory.

Immunity

Immunity memory cells in the blood make a person immune to the pathogen.

Part 2 of 8The secondary response

Recognition

Recognition on meeting the same antigen again, even years later, memory cells recognise it immediately.

Speed

Speed many more cells can respond, so they divide by mitosis and differentiate rapidly.
Memory B cells quickly become plasma cells and make antibodies.
Memory T cells quickly form cytotoxic and helper T cells.

Antibody timing

Antibody timing antibody appears within hours or a couple of days instead of a week or more.

Antibody level

Antibody level the peak is much higher and stays high longer.

Outcome

Outcome the pathogen is destroyed before it multiplies enough to cause symptoms.

Part 3 of 8Primary and secondary responses

Feature	Primary	Secondary
Lag phase	Several days	Very short
Peak antibody level	Low	High, often 10 to 100 times greater
Duration	Short	Long
Symptoms	Usually yes	Usually none
Cells involved	Naive lymphocytes	Memory cells

Part 4 of 8Interpreting antibody graphs

1First curve

First curve slow rise after a lag, a peak after perhaps 10 to 14 days, then decline.

2Second curve

Second curve a rise almost at once, a peak many times higher and a slower decline.

3Values

Values quote figures and calculate the ratio between peaks.

4Explanation

Explanation memory cells existed at the second exposure, giving rapid clonal expansion and differentiation into plasma cells.

5Different antigen

Different antigen a second exposure to another antigen gives a primary response again, because memory cells are specific.

6Decline

Decline antibody levels fall after the peak because plasma cells are short-lived and the antigen is gone, but memory cells remain.

Part 5 of 8Why some diseases recur

Stable antigens

Stable antigens memory cells give lasting protection against measles, chickenpox and mumps.

Variable antigens

Variable antigens colds and influenza recur because of many strains or antigen mutation,
- so memory cells for a previous strain fail to recognise the new one.

Malaria and HIV

Malaria and HIV the parasite varies or hides, and HIV destroys the helper T cells needed for the memory response.

Part 6 of 8Memory cells and active immunity

Vaccination

Vaccination a vaccine causes a primary response without disease, forming memory cells so a real infection meets a secondary response.

Boosters

Boosters repeated doses can raise protection.

Active immunity

Active immunity when memory cells form from the body's own response to infection or a vaccine, immunity lasts a long time.

Passive immunity

Passive immunity antibodies from another source,
- such as across the placenta or in breast milk, give immediate but temporary protection with no memory cells.

Part 7 of 8Antibody titre

Definition

Definition the concentration of antibodies against a pathogen.

Use

Use blood tests show whether a person was infected or vaccinated.

Interpretation

Interpretation a high titre indicates a recent or strong response, and a low titre may suggest a booster is needed.

Data

Data describe peaks and decline over time and relate them to dates of vaccination or infection.

Part 8 of 8More from the specification

Macrophage

A phagocyte in the alveoli that engulfs bacteria and particles.

Neutrophil

A phagocytic white blood cell with a multilobed nucleus.

Phagocytosis

The engulfing and digestion of pathogens by white blood cells.

Non-self

Foreign cells or molecules that are recognised by the immune system

Phagocyte

White blood cell that engulfs and digests pathogens.

Complementary

Having a matching shape.

Key terms

Term	Meaning
Memory cell	A long-lived lymphocyte that gives a rapid response to a repeated antigen.
Secondary response	The rapid, large response on re-exposure to an antigen.
Immunological memory	The ability to respond quickly to an antigen met before.
Antibody titre	The concentration of antibodies against a pathogen.
Lag phase	The delay before antibody appears.
Naive lymphocyte	A lymphocyte that has not yet met its antigen.

Avoid these mistakes

Saying memory cells make antibodies directly — they quickly become plasma cells that do.

Saying memory cells protect against any antigen — they are specific to one antigen.

Saying the secondary response gives the same antibody level — it is larger, faster and longer.

Saying passive immunity produces memory cells — it does not.

Last updated: 14 October 2026