Infliximab is made up of antibodies that are cloned from a single parent immune cell.  The antibodies bind to tumor necrosis factor alpha TNFa, a chemical messenger that is integral to the autoimmune response.  Infliximab causes the death of T_h1-helper cells which have a proinflammatory response, so limiting the activation of these cells are helpful in managing inflammation due to Crohn's Disease.

Adalimumab

Adalimumab is very similar to Infliximab and acts in the same way.  These drugs suppress the immune system and thus there is an increased risk of infection when taking it.

Natalizumab

Natalizumab is made from a human cloned antibody cell, and it does not act in the same manner as Infliximab and Adalimumab and so may be helpful in Crohn's Disease patients who do not respond to TNFa inhibitors.

Certolizumab