Answer:
Our immune system produces antibodies.
Step-by-step explanation:
Injecting an antigen from a pathogen would help our immune system memorize the infection and protect our body from causing of the disease because our immune system produces antibodies against that antigen so when the pathogen enters our body these antibodies attack on that and prevent them of causing infection in the body so that's why injecting an antigen has to be done from the childhood to prevent diseases.