"Walter teaches primary school and his class has suffered an outbreak of chickenpox (varicella). Walter notices that a number of the children who have previously suffered from chicken pox do not catch the infection during this outbreak." Does this scenario describe active or passive immunity? Is it natural or acquired? How is immunity gained? What is the difference between humoral and cellular response by B lymphocytes and T lymphocytes?

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The immunity that the children have in this scenario is active immunity. Active immunity can either be natural or acquired.

Natural immunity is gained when a person is infected with a certain disease. When pathogens (viruses, bacteria, fungi, parasites) or other foreign objects enter the body, they cause an infection....

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The immunity that the children have in this scenario is active immunity. Active immunity can either be natural or acquired.

Natural immunity is gained when a person is infected with a certain disease. When pathogens (viruses, bacteria, fungi, parasites) or other foreign objects enter the body, they cause an infection. As a result, the immune system is triggered; the white blood cells produce antibodies which recognize the antigen of the pathogen and protect the organism against severe illness.

Acquired immunity is gained through vaccination. Vaccines contain weakened versions of some pathogens. When a person receives a vaccine, their immune system responds similarly to the way it responds to a natural infection.

After a certain period of time, the antibodies formed in response to a natural infection or a vaccine will disappear; however, the memory B cells will remain in the body. Thus, if (or when) the body becomes infected with the same pathogen or foreign object, the immune system will immediately recognize the pathogen's antigen and promptly respond to it. This protects the body against severe illness or death.

The children in Mr. Walter's class that have been previously infected with the varicella-zoster virus won't catch the same disease (chickenpox) when they're exposed to it again. This situation is a clear example of active immunity gained from previous exposure or infection.

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