Which of the following vaccines is recommended for healthcare workers to protect against hepatitis B?

Explanation: At 2 months of age, infants are recommended to receive the DTaP vaccine, which protects against diphtheria, tetanus, and pertussis (whooping cough). The MMR vaccine protects against measles, mumps, and rubella and is usually administered at a later age. The hepatitis B vaccine is given shortly after birth, and the varicella vaccine is typically administered at 12 months of age.

Incorrect choices:

a. The MMR vaccine protects against measles, mumps, and rubella, not whooping cough (pertussis).

b. The hepatitis B vaccine is typically given shortly after birth, not at 2 months of age.

d. The varicella vaccine is usually administered at 12 months of age, not at 2 months.

Explanation: During cell-mediated immunity, T cells recognize antigens that are presented by antigen-presenting cells (APCs) such as macrophages. Macrophages engulf and process pathogens, and then they display fragments of the pathogens' antigens on their cell surface using major histocompatibility complex (MHC) molecules. T cells, specifically helper T cells, interact with these antigen-presenting macrophages and become activated to initiate immune responses.

Incorrect choices:
b. B cells present antigens to helper T cells during the humoral immune response, not during cell-mediated immunity.
c. Plasma cells are not involved in antigen presentation; they are terminally differentiated B cells that produce antibodies during the humoral immune response.
d. Memory cells are formed after the immune system encounters an antigen and are not directly involved in antigen presentation.