Which type of immunity is acquired when an individual's immune system is exposed to a pathogen through vaccination or natural infection?

Explanation: During antibody-mediated immunity, B cells produce antibodies, also known as immunoglobulins. Antibodies are Y-shaped proteins that specifically recognize and bind to antigens on the surface of pathogens or foreign substances. This binding marks the pathogens for destruction by other immune cells or neutralizes their harmful effects.

Incorrect choices:

a. Cytokines are small proteins that serve as signaling molecules in the immune system, regulating the behavior and activity of immune cells. B cells can secrete cytokines, but their primary function is antibody production.

b. Cytotoxic granules contain substances like perforin and granzymes and are released by cytotoxic T cells to induce apoptosis in infected or abnormal cells. B cells do not produce cytotoxic granules.

d. Perforin is a protein released by cytotoxic T cells and natural killer cells to create pores in the membrane of infected cells, leading to cell death. B cells do not produce perforin.

Explanation: Live attenuated vaccines use a weakened form of the pathogen that is still capable of replicating but does not cause severe illness in healthy individuals. This type of vaccine can provide long-lasting immunity with a single dose.

Incorrect choices:

a. Inactivated vaccines use killed pathogens, not weakened forms.

b. Subunit vaccines use only specific parts of the pathogen, not weakened forms.

d. Toxoid vaccines use inactivated toxins produced by the pathogen, not weakened forms of the pathogen itself.