This memory aid covers Memory Aids within Adaptive Immunity and Antibodies for GCSE Biology. Specific immune responses, antibody production, lymphocytes, memory cells It is section 14 of 18 in this topic. Use it for quick recall, then test yourself straight afterwards so the memory aid becomes usable in an answer.
Topic position
Section 14 of 18
Practice
20 questions
Recall
25 flashcards
Memory Aids
Antigen = ANTIbody GENerator: The word antigen literally contains "anti" and "gen" — it is the molecule that generates an antibody response. Any time you see "antigen" in an exam question, think: this is the specific molecule on the pathogen that the immune system recognises and responds to.
The lock-and-key for immunity: The antigen is the key; the B cell receptor (and subsequent antibody) is the lock. Only the key with the right shape fits. This is why each antibody is specific to one antigen — the shapes must be complementary.
Primary vs Secondary response — SSFL:
- Primary: Slow, Small antibody production, takes 5-10 days, Forms memory cells
- Secondary: Speedy, Stronger/larger antibody production, takes 1-3 days, memory cells already present (Lasting immunity)
B cell fate after activation: Most B cells become plasma cells (antibody factories). Some become memory B cells (long-lived sentinels). Think "most go to work now, some keep watch for later."
T cell types: Helper T cells = the coordinator (calls in reinforcements, activates B cells). Cytotoxic T cells = the assassin (directly kills infected body cells). Memory T cells = the veteran (ready for the next encounter).
Quick Check: A person is infected with influenza for the first time. Explain why they develop symptoms for 7-10 days before recovering, whereas on a second exposure to the same flu strain they may not develop symptoms at all.
During the primary response to the first infection, the immune system must first recognise the viral antigens, select the appropriate B cells through clonal selection, and expand the clone. This takes 5-10 days before sufficient antibodies are produced to clear the infection. During this time, the virus multiplies and causes tissue damage — producing symptoms. However, memory B cells are also produced during this primary response. On second exposure to the same flu strain, memory B cells respond immediately (within 1-3 days) and rapidly produce large amounts of antibodies. The virus is eliminated before it can multiply sufficiently to cause tissue damage, so no symptoms (or only very mild ones) develop. This is the principle that underlies vaccination.
Quick Check: Explain why a person who has recovered from measles is protected for life, but someone who recovers from influenza needs a new vaccine every year.
After recovering from measles, the immune system produces memory B and T cells specific to the measles virus antigens. The measles virus has very stable surface antigens that do not change significantly between strains or over time. So the same memory cells remain effective for the person's lifetime. Influenza virus, however, undergoes rapid mutations (antigenic drift) in its surface proteins (haemagglutinin and neuraminidase). Each year, new influenza strains circulate with slightly different surface antigens. Memory cells produced against last year's strain do not recognise the new antigens, so the person is not protected. New vaccines are formulated each year targeting the antigens predicted to be on the dominant circulating strains.
Quick Check: A scientist injects a mouse with antigen X. Three weeks later, she measures the antibody levels in the mouse's blood, which are high. She then gives the same mouse a second injection of antigen X. Predict and explain what happens to the antibody level over the next two weeks.
After the second injection, the antibody level would rise much faster (within 1-3 days) and to a much higher level than after the first injection. This is because the first injection triggered a primary immune response that produced memory B cells specific to antigen X. These memory cells persist in the blood and lymph nodes. When antigen X is introduced again, the memory B cells rapidly divide and differentiate into plasma cells, which secrete large quantities of antibodies very quickly. The response is faster, larger, and longer-lasting than the primary response. This demonstrates immunological memory — the basis of vaccination.