Does a reply to comment count as a publication? Years ago, I published a paper with some collaborators, and recently a comment to the paper has been submitted. Together with the other authors, we published a reply to comment, which has been published on the journal. 

Is it reasonable to list the reply as a publication in my CV, in addition to the original paper?
Yes, but you would probably want to make separate lists of refereed and non-refereed publications. By putting the comment in the latter list, you do show that you engage with academic discussion, but you do not overclaim it as yet another refereed publication.