Why are booster doses of some vaccines recommended?

Explanation: Memory in the immune system refers to the ability of immune cells, particularly memory B cells and memory T cells, to recognize and respond more quickly and effectively to specific antigens upon subsequent exposure. This leads to a faster and stronger secondary immune response.

Incorrect choices:
b. The ability of immune cells to differentiate between self and non-self antigens refers to the concept of immune tolerance, which helps prevent the immune system from attacking the body's own cells and tissues.
c. The process of phagocytosis by macrophages is a mechanism by which immune cells engulf and destroy pathogens and cellular debris, but it is not directly related to memory in the immune system.
d. The ability of B cells to produce antibodies is an essential part of the primary immune response, but it is not specific to memory in the immune system.

Explanation: B cells recognize antigens by producing specific receptors on their cell surface, known as antibodies or immunoglobulins. When a B cell encounters an antigen that matches its specific antibody, it binds to the antigen, marking it for destruction or neutralization by other immune cells.

Incorrect choices:

a. Engulfing and processing pathogens is the role of antigen-presenting cells like macrophages and dendritic cells. These cells present processed antigens to other immune cells, including B cells, to trigger an immune response.

b. Cytokines are small proteins that serve as signaling molecules in the immune system. They are produced by various immune cells to regulate immune responses, but they are not directly involved in antigen recognition by B cells.

d. Directly attacking and killing infected cells is the role of cytotoxic T cells during cell-mediated immunity, not B cells during the humoral immune response.