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

Explanation: B cells are a type of lymphocyte that produces antibodies against specific antigens. When a B cell encounters an antigen that matches its specific receptor, it becomes activated and differentiates into plasma cells, which are responsible for producing large quantities of antibodies that can target and neutralize the antigen.

Incorrect choices:

b. T cells are involved in cell-mediated immunity and do not produce antibodies. They recognize and directly attack infected or abnormal cells in the body.

c. Macrophages are antigen-presenting cells that engulf and process pathogens to present their antigens to other immune cells. They do not produce antibodies themselves but play a role in initiating the immune response.

d. Natural killer cells are a type of lymphocyte involved in the innate immune response. They do not produce antibodies but can directly kill infected or abnormal cells.

Explanation: Memory cells recognize and respond rapidly to previously encountered pathogens. Memory cells are a type of immune cell that are formed after an initial infection or vaccination. They "remember" the specific pathogen and allow the immune system to mount a faster and stronger response upon subsequent exposures to the same pathogen, providing long-term immunity.

Incorrect choices:

a. Memory cells do not directly attack pathogens in the body. They serve as a form of immune "memory" to help the body respond more effectively to future infections.

b. Memory cells do not produce antibodies upon initial pathogen exposure. B cells are responsible for producing antibodies in response to the pathogen.

d. Memory cells do not regulate the body's temperature during an infection. Temperature regulation is mainly controlled by the hypothalamus in the brain in response to infection or other stimuli.