Editing a book of this nature was a simultaneously exhilarating and frightening experience. It was exhilarating to draw from cell biologists, biochemists, and molecular biologists, as well as those dermatologists, pathologists, and pul monologists who are cell biologists at heart, to author chapters. At the same time, it was frightening to ask such busy investigators to devote their precious time to writing chapters that summarize not just their own endeavors but their entire area of expertise. However, the authors assuaged our fears by enthusi astically accepting the proposal to write on...