Which of the following types of vaccines involves the use of a weakened form of the pathogen?

Explanation: Hormones are chemical messengers produced by the endocrine system to regulate various physiological processes in the body. While the endocrine system and immune system can influence each other's activities, hormones are not considered a direct component of the immune system.

Incorrect choices:

a. Lymphocytes are a type of white blood cell and a critical component of the immune system. They include B cells, T cells, and natural killer cells, which play essential roles in immune responses.

b. Antigens are molecules or substances that can trigger an immune response in the body. They are recognized by the immune system as foreign or non-self and can elicit the production of antibodies.

d. Antibodies are proteins produced by B cells in response to the presence of antigens. They play a vital role in recognizing and neutralizing foreign substances in the body.

Explanation: T cells are a type of lymphocyte that plays a crucial role in cell-mediated immunity. They are responsible for recognizing and directly attacking infected or abnormal cells in the body. There are two main types of T cells: cytotoxic T cells, which directly kill infected cells, and helper T cells, which assist in coordinating the immune response.

Incorrect choices:

a. B cells are responsible for the production of antibodies and are involved in the humoral immune response, which targets pathogens outside of cells. They do not directly recognize and destroy infected cells.

c. Macrophages are antigen-presenting cells that engulf and process pathogens to present their antigens to other immune cells. While they are involved in immune recognition, they do not primarily recognize and destroy infected cells.

d. Neutrophils are a type of white blood cell involved in the innate immune response. They primarily target and destroy bacteria and other foreign invaders in the body, but they do not have the specific recognition capabilities of T cells.