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← Theoretical 2

Q79 — Primary vs Secondary Antibody Response

Theoretical 2 Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Immune Physiology

It is known that the humoral immune system responds to antigens entering an organism by producing antibodies. The diagram shows the immune response (production of antibodies) during the initial (first) and repeated (secondary) introduction of the antigen. Note that the time from infection to the presence of a significant amount of antibody in the bloodstream is called a latent period.

Graph of relative antibody production (logarithmic scale) versus time in days. After the first injection of antigen A at day 0, a slow-rising, low-magnitude “primary response to antigen A” peaks around day 15-17 and then declines. At day 40, a second injection of antigen A together with a first injection of antigen B is given. The response to antigen A now rises rapidly to a much higher peak (a “secondary response to antigen A”), while the response to antigen B shows the same slow, low-magnitude kinetics as a first-time (“primary”) response, peaking later and much lower than the secondary response to A. Relative intensity of antibody production (log scale) over time, showing the primary response to antigen A, the secondary response to antigen A after a second injection, and the primary response to antigen B given at the same time as the second injection of antigen A.

Using this information, determine whether the following statements are true or false.

A. After a second injection of antigen A not only quantity, but also quality (eg. affinity) of the antibodies are substantially enhanced.
B. Any antigenic stimulation nonspecifically activates the immune system leading to generally stronger and quicker humoral response to all antigens.
C. Secondary response against antigen A benefits from already differentiated antigen-specific B cells and helper T cells from the primary response.
D. Primary response to antigen A is due to rapid innate immune mechanisms like phagocytosis of the antigen, localized in immunized tissue.
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Question reproduced from IBO 2022, Theoretical Paper 2, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)