Thread has been opened but not all posts within the thread have been read. Title should not be bold.
As mentioned in mock ups that bold text of post indicates that the thread has never been opened. But when user reads a post and he himself or any other user adds any response/comment to that read post, app changes the post text back to bold. It shouldn't change the already read post text to bold on adding responses/comments.
1) Create a new post.
2) Read that newly created post.
3) Add a response/comment and view.