How does the immune system distinguish between self and non-self?

Explanation: Macrophages are a type of white blood cell that plays a crucial role in the innate immune response. They are phagocytes, meaning they engulf and destroy pathogens, cellular debris, and foreign substances in the body. Macrophages are also antigen-presenting cells, as they process and present antigens to other immune cells to initiate an adaptive immune response.

Incorrect choices:

a. B cells produce antibodies against specific antigens but do not directly engulf and destroy pathogens.

b. T cells are involved in cell-mediated immunity and directly attack infected or abnormal cells but do not have phagocytic capabilities like macrophages.

d. Natural killer cells are a type of lymphocyte involved in the innate immune response and can directly kill infected or abnormal cells, but they do not primarily function as phagocytes like macrophages.

Explanation: Passive immunity is acquired when preformed antibodies are transferred to an individual, providing immediate but temporary protection against a specific pathogen. This can occur naturally from a mother to her newborn or artificially through administration of specific antibodies.

Incorrect choices:

a. Active immunity is acquired when the body's immune system is exposed to a pathogen and produces an immune response to provide protection against future infections.

c. Natural immunity refers to immunity that is acquired through natural exposure to a pathogen, either through infection or vaccination.

d. Herd immunity is the indirect protection that occurs when a large percentage of a population becomes immune to a disease, either through vaccination or previous infection, reducing the likelihood of transmission to susceptible individuals.