To Generate a Vaccine to Pertussis Toxin, a Heat-Killed Preparation

To generate a vaccine to pertussis toxin, a heat-killed preparation of Bordetella pertussis (the bacteria that produce pertussis toxin) is mixed with a purified preparation of the inactivated toxin protein. The mixture is then injected subcutaneously into mice. In an effort to enhance the antibody response to the toxin, a group of test mice is depleted of all their dendritic cells immediately prior to immunization. However, instead of enhancing the antibody response, the dendritic cell depletion nearly eliminated the anti-toxin antibody response because:

A) All of the toxin-specific B cells underwent apoptosis in the absence of dendritic cells.
B) The heat-killed Bordetella pertussis could not be ingested by macrophages in the mice.
C) Dendritic cells are needed to activate naive CD4 T cells, which can then help the B cells produce anti-toxin antibody.
D) The macrophages in the mice did not express the appropriate pattern recognition receptors to recognize Bordetella pertussis.
E) The toxin-specific B cells did not up-regulate their MHC class II molecules after encountering the Bordetella pertussis.