Which type of immune response is the body's first line of defense against infections?

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.

Explanation: Receiving antibodies through placenta during pregnancy. Passive immunity is acquired when preformed antibodies are transferred from one individual to another, providing immediate but temporary protection. This can occur naturally through breastfeeding or artificially through administration of preformed antibodies, as in the case of placental transfer of antibodies from a mother to her baby.

Incorrect choices:

a. Receiving a flu vaccine involves active immunity, where the body is exposed to an attenuated or inactivated pathogen to stimulate the production of antibodies and memory cells for long-term protection.

b. Developing immunity after recovering from a viral infection is an example of active immunity, where the body mounts an immune response and produces memory cells to provide long-lasting protection against the pathogen.

d. Producing memory cells after exposure to a pathogen is part of the adaptive immune response and contributes to long-term immunity, not passive immunity.