Editing Exotoxin (section)

==== By mode of entry ====
Intracellular toxins must be able to gain access to the cytoplasm of the target cell to exert their effects.

* Some bacteria deliver toxins directly from their cytoplasm to the cytoplasm of the target cell through a needle-like structure.  The effector proteins injected by the type III [[secretion]] apparatus of ''[[Yersinia]]'' into target cells are one example.
* Another group of intracellular toxins is the [[AB toxin]]s.  The 'B'-subunit ('''''b'''inding'') attaches to target regions on cell membranes, the 'A'-subunit ('''''a'''ctive'') enters through the membrane and possesses [[enzymatic]] function that affects internal cellular bio-mechanisms. A common example of this A-subunit activity is called [[ADP-ribosylation]] in which the A-subunit catalyzes the addition of an ADP-ribose group onto specific residues on a protein.  The structure of these toxins allows for the development of specific [[vaccine]]s and treatments. Certain compounds can be attached to the B unit, which is not, in general, harmful, which the body learns to recognize, and which elicits an [[immunity (medical)|immune response]]. This allows the body to detect the harmful toxin if it is encountered later, and to eliminate it before it can cause harm to the host. Toxins of this type include [[cholera toxin]], [[pertussis toxin]], [[Shiga toxin]] and heat-labile [[enterotoxin]] from ''E. coli''.