When bacteria such as Listeria and Salmonella
are taken up into a phagocytic cell of the immune system, they are
engulfed into a phagocytic vacuole in the interior of the cell.
Here they may be destroyed and fragments of antigens they carry
will eventually egress to the cell surface to activate CD4 immune
cells, which are important in assisting in the immune response.
Listeria, unlike other bacteria, has evolved to break out
of the vacuole and survive inside the immune cell. This way antigens
that Listeria carries are targeted to a pathway in the
cytoplasm where they are broken into peptides and taken to the cell
surface for recognition by killer T cells. These killer T cells
seek out and destroy tumor cells displaying tumor-specific antigens.
Credit: Yvonne Paterson, PhD, University of Pennsylvania School