True or False: Vaccines can cause autism in children.

Explanation: Active immunity is acquired when the body's immune system is exposed to a pathogen through vaccination or natural infection and produces an immune response to provide protection against future infections.

Incorrect choices:

b. Passive immunity is acquired when preformed antibodies are transferred to an individual, providing immediate but temporary protection against a specific pathogen.

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.

Explanation: The primary role of B cells during the humoral immune response is to produce antibodies against specific antigens on pathogens. When B cells encounter an antigen that matches their specific receptor, they become activated and differentiate into plasma cells, which then secrete large amounts of antibodies into the bloodstream.

Incorrect choices:

a. Antigen presentation to B cells is carried out by antigen-presenting cells, such as macrophages and dendritic cells, not by B cells themselves.

c. 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.

d. The regulation of the immune response is mainly the function of regulatory T cells (Tregs) and other immune regulatory mechanisms, not the primary role of B cells.