True or False: Vaccines can cause autism in children.

Correct answer: C

A.B cells are part of the adaptive immune system and are responsible for antibody-mediated immunity. They do not directly attack and kill infected cells. Instead, B cells produce antibodies that can recognize and neutralize pathogens or foreign substances.

b. B cells are involved in antibody-mediated immunity, not cell-mediated immunity. They produce antibodies that circulate in the bloodstream and bind to antigens on pathogens, marking them for destruction by other immune cells.

c. B cells are crucial for recognizing "foreign" molecules (antigens) on pathogens and producing antibodies that can bind to those antigens. Macrophages engulf pathogens and present fragments (antigens) of them on their surface, allowing B cells to identify and target the specific pathogen.

d. Phagocytosis of pathogens is mainly carried out by macrophages and neutrophils, not B cells.

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.