Efalizumab binds to CD11a, a subunit of leukocyte function antigen-1 (LFA-1), which is expressed on all leukocytes. As a result efalizumab decreases cell surface expression of CD11a.
Lymphocyte activation and trafficking to skin play a role in the pathophysiology of chronic plaque psoriasis. In psoriatic skin, ICAM-1 cell surface expression is upregulated on endothelium and keratinocytes. Raptiva inhibits the binding of LFA-1 to the intercellular adhesion molecule-1 (ICAM-1), thereby inhibiting the adhesion of leukocytes to other cell types.