Which of the following vaccines is typically recommended for older adults to prevent complications from pneumonia?

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.

Explanation: Cytotoxic T cells (CD8+ T cells) are the effector cells of cell-mediated immunity. Their primary role is to directly recognize and kill infected or abnormal cells, such as virus-infected cells or cancer cells. Cytotoxic T cells release cytotoxic granules containing perforin and granzymes, which induce apoptosis (cell death) in the target cells.

Incorrect choices:

a. Helper T cells, not cytotoxic T cells, recognize antigens presented by macrophages and play a crucial role in activating other immune cells.

b. B cells are responsible for producing antibodies against pathogens during the humoral immune response, not cytotoxic T cells.

d. Regulatory T cells (suppressor T cells) are involved in regulating the immune response to prevent excessive inflammation and tissue damage, not cytotoxic T cells.