Underlining appears like this:
_^Hu_^Hn_^Hd_^He_^Hr_^Hl_^Hi_^Hn_^Hi_^Hn_^Hg
You can destructively remove underlining with M-x ununderline-region.
For ClariNews articles, clari-clean.el by David N. Blank-Edelman <dnb@meshugge.media.mit.edu> will remove both underlining and overstriking automatically.