Some People Are Immune to Certain Diseases
We become immune to germs through natural and artificial means. As long ago as the 5th century B.C., Greek doctors noticed that people who had recovered from the plague would never get it again —they seemed to have become immune or resistant to the germ.You can become immune, or develop immunity ,to a microbe in several ways. The first time T cells and B cells in your immune system meet up with an antigen ,such as a virus or bacterium,they prepare the immune system to destroy the antigen.Because the immune system often can remember its enemies,those cells become active if they meet that particular antigen again.This is called naturally acquired immunity.
Another example of naturally acquired immunity occurs when a pregnant woman passes antibodies to her unborn baby.Babies are born with weak immune responses ,but they are protected from some diseases for their first few months of life by antibodies received from their mothers before birth.Babies who are nursed also receive antibodies from breast milk that help protect their digestive tracts.
Artificial immunity can come from vaccines. Immunization with vaccines is a safe way to get protection from germs. Some vaccines contain microorganisms or parts of microorganisms that have been weakened or killed.If you get this type of vaccine,those microorganisms (or their parts)will start your body ’s immune response,which will
demolish the foreign invader but not make you sick.This is a type of artificially acquired immunity.
Immunity can be strong or weak and short-or long-lived, depending on the type of antigen,the amount of antigen, and the route by which it enters your body.When faced
with the same antigen,some people ’s immune system will respond forcefully, others feebly, and some not at all. The genes you inherit also can influence your likelihood
of getting a disease. In simple terms, the genes you get from your parents can influence how your body reacts to certain microbes.