Which of the following are part of the first line of defense against invaders: (select all that apply)

A. None of the answers are correct is incorrect because one of the options does result in active immunity.
B. Antiserum administration involves the transfer of antibodies (passive immunity), not the activation of the immune system to produce its own antibodies.
C. Vaccination induces active immunity by stimulating the immune system to produce its own antibodies and memory cells in response to a weakened or inactivated pathogen (or its components). This prepares the body for future exposure to the actual pathogen.
D. Breast feeding provides passive immunity because the infant receives pre-formed antibodies from the mother through breast milk, but does not stimulate the infant's immune system to produce its own.

A. Attenuation is the process of weakening or reducing the virulence (ability to cause disease) of a pathogen, making it less harmful. This weakened form can then be used in the preparation of vaccines, allowing the immune system to respond without causing disease.
B. Antitoxin refers to antibodies or other substances that neutralize toxins, not the process of reducing a pathogen's virulence.
C. Complement refers to a group of proteins that play a role in the immune response, enhancing the ability to clear pathogens, but it is not related to the process of preparing vaccines.
D. Vaccine is a preparation used to stimulate the immune system, but the process of preparing the vaccine (such as attenuation) is different from the vaccine itself.