Tom has just been exposed to the measles virus, and he can't remember if he has had measles before. He asks you if there is any way he can tell if he has been previously exposed or if he is going to get sick. What would you tell him? Why won't he get sick from a second infection?
What will be an ideal response?
If Tom has previously had the measles, there should be a significant amount of IgG antibody in his blood shortly
after the most recent exposure, as a result of a secondary humoral immune response. If he has not previously had
the disease and is in the early stages of a primary response, his blood might show an elevated level of IgM type
antibodies. These are the first to be produced in a primary response and are ultimately replaced by IgG antibodies.
IgG antibodies are able to mount a more vigorous and immediate response to subsequent exposures, preventing
illness.
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