A)an interferon.
B)lymphatic fluid.
C)histamine.
D)mucus.
E)sodium ions.

A)is activated immediately upon infection.
B)depends on a newly infected animal's previous exposure to the same pathogen.
C)is based on recognition of antigens that are specific to different pathogens.
D)is found only in vertebrate animals.
E)utilizes highly specific antigen receptors on B cells.

A)lysosomes.
B)mast cells.
C)neutrophils.
D)immunoglobulins.
E)dendritic cells.