After antigen exposure, which of the following does the immune system produce against foreign substances?

The immune system's response to foreign substances, known as antigens, involves the production of lymphocytes and antibodies. Lymphocytes are a type of white blood cell that plays critical roles in the immune response. There are various types of lymphocytes, primarily B cells and T cells. B cells are responsible for producing antibodies, which are proteins that specifically recognize and bind to antigens. This binding can neutralize pathogens or mark them for destruction by other components of the immune system.

Antibodies, on the other hand, are crucial for the adaptive immune response. Upon first exposure to an antigen, the immune system generates specific antibodies tailored to that antigen. These antibodies remain in the body and can provide long-lasting immunity, allowing for a faster and more effective response upon subsequent exposures to the same antigen.

The other choices do not pertain to the immune response to antigens. Red blood cells are primarily involved in oxygen transport and do not play a role in fighting infections or recognizing foreign substances. Platelets are essential for blood clotting rather than immune defense. Hormones and enzymes, while vital in other biological processes, do not directly participate in the immune response against antigens.