it's ctrl+r (\022) but using this for most clients reverses the foreground/background. Mostly because using fixed width fonts (irc friendly) there is no such thing as italic.
interweb wrote:Italic text can also be used. However, because some clients are incapable of rendering italic text, you will find that most clients (including those that can render italic text) display this as normal text with the background and foreground colors swapped. For this reason, it is also known as reversed text formatting and can be achieved in mIRC by pressing Ctrl-R.