Kupffer cells are phagocytes located in the:

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. T cells "mature" and become fully functional in the thymus – T cells are produced in the bone marrow, but they mature in the thymus. In the thymus, T cells undergo a selection process to become functional and capable of recognizing specific antigens.
B. T cells are produced by stem cells in bone marrow – T cells originate from stem cells in the bone marrow, where they first begin to develop. However, they mature in the thymus.
C. T cells are produced in the spleen – This is incorrect. While the spleen plays a role in immune responses, T cells are not produced there; they are produced in the bone marrow.
D. T cells "mature" and become fully functional in the tonsils – This is incorrect. Tonsils are part of the lymphatic system and play a role in immune defense, but T cells do not mature there; they mature in the thymus.