Question Video: Identifying the Secondary Immune Response from a Graph of Antibody Production | Nagwa Question Video: Identifying the Secondary Immune Response from a Graph of Antibody Production | Nagwa

Question Video: Identifying the Secondary Immune Response from a Graph of Antibody Production Biology • Third Year of Secondary School

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The graph provided shows the primary and secondary immune response in relation to antibodies produced. Which line represents exposure for the second time to the original antigen?

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Video Transcript

The graph provided shows the primary and secondary immune response in relation to antibodies produced. Which line represents exposure for the second time to the original antigen?

Let’s start by looking at the time it takes for primary and secondary immune responses. The primary response occurs after the first exposure to an antigen. The response takes almost a week to begin. During this lag period, B cells and T cells go through clonal selection and clonal expansion, while the innate immune system fights the infection using antigen-nonspecific methods. Clonal selection is where a B cell or T cell is selected for cloning because it has receptors which recognize specific antigens on the infecting pathogen.

The selected cell then proliferates to produce many clones, which travel throughout the body and eliminate the pathogen. During the clonal selection phase, activated and memory immune cells are created. For example, memory B cells and activated and differentiated B cells, so-called plasma cells, which produce antibodies, are created. Memory T cells are also produced, but we will keep things simple by concentrating on B cells here.

The primary immune response does not reach its peak until more than two weeks have passed. Eventually, when the antigens are cleared, the primary immune response is shut down. Activated cells are removed from the system. And all that’s left behind after about five weeks are memory cells. The secondary immune response occurs as a result of a subsequent exposure to the same antigen. It is a much more rapid and sustained response due to the action of memory immune cells. The presence of memory cells means that there is no need for the time-consuming clonal selection process. B cells and T cells specific to the antigen are already prepared to rapidly become activated. More antibodies are made by more cells more quickly during the secondary response. These antibodies also persist in the blood for a longer time after the infection has been cleared.

From this information, we can see that during the secondary response, the body makes antibodies almost immediately after exposure. And there are more cells making more antibodies. The amount of antibodies will therefore increase rapidly. On the graph, we can see that line Y shows a rapid increase in antibodies — this occurs over less than one week — and that the amount of antibodies remains high for a longer period of time. Lines X and Z show long periods of time for the antibodies to increase. And the lines go almost flat after around five weeks, which correlates with the description of the primary immune response. Line Y represents the secondary immune response the best. So the answer to our question is Y.

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