Question: Passage $\mathrm{V}$
For many years, researchers have been interested in developing edible vaccines that would provide protection against various bacterial and viral diseases. An edible vaccine is a genetically modified organism (GMO) that is created when genes from the bacteria or virus being vaccinated against are inserted into plant cells. As the plants grow, they produce proteins from the bacteria or virus that the researchers are attempting to vaccinate against. When a person eats the plant, the viral or bacteria proteins serve as antigens, which initiates a primary immune response.
Some of the plants that are of interest in edible vaccine development are bananas, potatoes, tomatoes, corn, rice, tobacco, and soybeans. While early research focused on growing crops that produced edible products such as bananas, the most recent research is focused on extracting material from the leaves and seeds of the plants, dehydrating it, and putting it into capsules that can be swallowed. This allows for a more predictable dosage of the vaccine and eliminates concerns that the crops containing the vaccine would be accidentally eaten by individuals who are not in need of the vaccine. The term edible vaccine has now been replaced with the term plantderived oral vaccine.
The development of plant-derived oral vaccines solves many problems associated with injectable vaccines. Because plant-derived oral vaccines are grown in crops, there is no problem with storage or refrigeration that is required of most traditional vaccines. These plant-derived vaccines also require no special training to administer. Additionally, when a vaccine is taken orally, it provides mucosal immunity due to the production of IgA antibodies by the immune system-in addition to systemic immunity. Since 90 percent of diseases enter the body through a mucus membrane, a vaccine that coerces mucosal immunity is of great benefit in the prevention of many diseases.
Suppose that an individual has been given a plant-derived oral vaccine against a specific virus. How could you determine whether the vaccine was effective?

Options:
A. Test for the presence of interleukins in the blood of the patient.
B. Test for the presence of interferons in the blood of the patient.
C. Test to determine whether the complement system in the blood had been activated.
D. Test for the presence of antibodies to the viral antigen.
Answer: This question relies on knowledge of the immune response. Interleukins are cytokines that are secreted during the process of clonal selection in primary immune responses. Since they are not specific toward any one particular antigen, choice A can be eliminated. Interferons are produced as nonspecific defenses against viral infections. Virally infected cells secrete interferons that are detected by neighboring cells. Secretion of interferons gives neighboring cells the chance to increase their immune defenses so that they do not become infected by the virus. Since interferons are nonspecific, their presence would not indicate immunity against a specific virus, which eliminates choice B. The components of the complement system circulate in the plasma and are activated by bacteria that may enter the blood. Activation of the complement system ultimately lyses and kills the bacterial cell. Since the question is asking about a virus, choice C can be eliminated because it deals with bacteria. This leaves choice $\mathrm{D}$ as the correct response. The detection of antibodies against the viral antigen would indicate that specific defenses were initiated and that plasma cells were activated to secrete antibodies against the viral antigen that was presented by the vaccine. The correct answer is D.