Immunology

Question:

In the Haemophilus influenzae type b vaccine, the bacterial capsular polysaccharide is conjugated to a carrier protein to improve immunogenicity in children. Which of the following cells become activated following contact with peptides processed from this vaccine in the context of MHC type II proteins?

Correct Answer: E.  T lymphocytes

Logically, a vaccine needs to work by inducing memory cells. There are two types of memory cells – T and B. Memory B cells (a variant of plasma cells) can only be produced after signaling from activated T cells. Thus, the vaccine will need to lead to the activation of T cells.

The carrier protein in the vaccine enables it to be taken up and processed by antigen-presenting cells (dendritic cells, B cells, macrophages). The peptides are presented on MHC type II, which contact and activate T-lymphocytes, starting the above immune cascade.