How do Tysabri and Cimzia work?

The Los Angeles Times has a good description of how two of the latest Crohn's medications operate:

Cimzia is also a TNF blocker, but unlike the others it contains only part of the antibody -- the portion that recognizes TNF. The rest of the antibody -- the part that can induce its own immune response -- is replaced with a compound called PEG.

This PEG tail stabilizes the drug, allowing it to stay in the patient's body much longer[...].

That means patients would only require treatment every other month, as opposed to every other week with Humira.

During inflammation, infection-fighting white blood cells of the immune system cruise through capillaries, searching for infection. When tissues are infected, they put out signals to slow down the blood cells and coax them to enter the tissue. [...]

Tysabri binds to those exit signs -- blocking them from recognition by the immune cells that are causing the Crohn's. So the white blood cells keep on moving, and the course of inflammation is stopped.

It'll be exciting to see how well these drugs operate on a wider variety of Crohn's patients, if and when they are approved.