Question Video: Identifying Immune Responses Involved with Two Infections with Different Pathogens Biology

A person is infected with a strain of rhinovirus that causes the common cold. A few weeks later, they are infected with a strain of morbillivirus that causes measles. Assuming this is the first time they are exposed to the measles virus, which of the following statements is correct? [A] The person will experience a secondary immune response to the morbillivirus and will quickly produce antibodies to fight off this infection. [B] The person will not experience a secondary immune response to the measles virus because they have been infected with two different pathogens. [C] The person will have a much weaker immune system after being infected with a cold and will not survive the measles infection. [D] Upon initial infection with the cold virus, the person’s primary immune response will produce antibodies to fight off a wide range of viral and bacterial infections.

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Video Transcript

A person is infected with a strain of rhinovirus that causes the common cold. A few weeks later, they are infected with a strain of morbillivirus that causes measles. Assuming this is the first time they are exposed to the measles virus, which of the following statements is correct? Option (A), the person will experience a secondary immune response to the morbillivirus and will quickly produce antibodies to fight off this infection. Option (B), the person will not experience a secondary immune response to the measles virus because they have been infected with two different pathogens. Option (C), the person will have a much weaker immune system after being infected with a cold and will not survive the measles infection. Or option (D), upon initial infection with the cold virus, the person’s primary immune response will produce antibodies to fight off a wide range of viral and bacterial infections.

The question asks about a person who is infected with a strain of rhinovirus followed by a strain of morbillivirus a few weeks later. Our answer choices discuss primary and secondary immune responses. So, let’s remove the answer options for now to get a bit of space to review these before trying to answer our question.

Primary and secondary immune responses are responses carried out by the adaptive immune system. The adaptive immune system uses specialized immune cells, specifically B cells and T cells, to fight a pathogen. It is called adaptive because it learns to recognize the pathogen after a first infection so that it is adapted to this pathogen in case the body should be infected by it for a second time. A successfully fought infection therefore makes the immune system stronger as it is difficult for a pathogen to successfully cause an infection in a body that recognizes it. The primary immune response occurs when the immune system encounters a pathogen for the very first time. This is a slow process because the body is not prime to recognize antigens on the invading pathogen yet.

Here, an antigen refers to a specific structure on the pathogen itself, or on the toxins that it secretes. During this recognition phase, B cells and T cells learn to recognize the antigen that is specific to this particular pathogen. During the primary immune response, cells with the ability to recognize the pathogen clone themselves. This process is called clonal expansion. Some of the clones are activated to fight the infection. For example, B cells become plasma cells which secrete antibodies. Some turn into memory cells in active immune cells that can survive for many years within immune organs. You can think of this as the immune system memorizing the specific antigen so that it can mount the response more quickly if the same pathogen infects the body again in the future.

Once the pathogen is destroyed, the active cells die, but a pool of memory cells remains. If the same invading pathogen were to infect an individual for a second time, memory cells will recognize it and initiate the secondary immune response. The secondary immune response is much faster than the primary immune response because by recognizing the foreign invader, more immune cells against the pathogen can be created fast. If the same invading pathogen were to infect an individual for a second time, memory cells will recognize it and initiate the secondary immune response. As the graph shows, the secondary response begins almost immediately and is much faster than the primary immune response. Due to the quick recognition of the foreign invader, more immune cells against the pathogen can be quickly created.

Now that we’ve discussed how the primary and secondary immune responses work, let’s take another look at our answer options. We have just seen how if a person is reinfected with the same strain of the pathogen, a secondary immune response will occur. Therefore, if a person is reinfected with the same strain of the rhinovirus, a secondary immune response would occur. However, we are told that the person is infected with a different virus altogether, the morbillivirus. Because memory cells are specific to their respective pathogen, the individual will then experience another primary immune response to the morbillivirus.

Now that we’ve discussed this situation in detail, we are able to answer our question correctly. In response to the question “which of the following statements is correct?” we should select answer choice (B). The person will not experience a secondary immune response to the measles virus because they have been infected with two different pathogens.

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