Which one of the following is NOT a part of the human non-specific defense system?

Which one of the following amino acids is catalyzed by activated macrophages to produce reactive nitrogen species?

Recombinant live attenuated vaccine against hepatitis B was prepared from

Which of the following statements about immune response are correct?
P. T cells are activated by antigen-presenting cells.
Q. Foreign peptides are not presented to helper T cells by class II MHC proteins.
R. Dendritic cells are referred to as professional antigenpresenting cells.

Which one of the following complement proteins is the initiator of the membrane attack complex?