The world’s top antiquarian book sellers and collectors will be in town this weekend for the 43rd Boston International Antiquarian Book Fair, hosted by “Antiques Roadshow” appraiser Ken Gloss. WGBH’s Henry Santoro spoke to Gloss, longtime owner of Boston’s Brattle Book Shop, about the fair and the “extraordinary finds” to be made there. The transcript below has been edited for clarity.

Henry Santoro: Would you say that the antiquarian book fair is like one huge “Antiques Roadshow,” only devoted strictly to books, maps, manuscripts and other printed matter?

Ken Gloss: Yes, in a way, although it's more of an investigation for the people coming in — because the dealers know what they have. But you can go into that show, and you can touch and hold letters by George Washington or Thomas Jefferson, first editions of Charles Dickens, books that were printed back in in the 1400s. There's about 130 dealers coming from all over the world, and they have their displays, and they bring their items. They'll hand you something that maybe Albert Einstein once had or even something as recent as the first Harry Potter books. And you can see and touch and hold and feel them, and that's part of what the fair is about.

Santoro: "Antiques Roadshow" recently celebrated its 500th episode with a show devoted to what it calls “extraordinary finds.” It was a massive hit. Have you ever had the pleasure of appraising one of these extraordinary finds?

Gloss: I appraised a letter that a soldier had written home from a hospital in Washington. He said, “I love getting letters. Please write me — it really helps. I think I'm getting better.” At the end of the letter, though, it said it was written by the soldier’s friend Walt Whitman. So the whole letter was in Walt Whitman's handwriting. During the war, Whitman wasn't in the battlefield. He worked at the hospitals, and he would write out letters for soldiers who were either illiterate or too sick to write. So it was very exciting when one of those letters came into the roadshow. The lady who brought it in was thrilled. It was perfect.

But these are the types of things that we have at the book fair too, and you can actually see them in quantity.

Santoro: You know, monetary value is one thing, but you cannot put a price tag on sentimental value.

Gloss: I one time got a call from a lady, and the first thing she said was “President Kennedy slept with me!” Well, you have to admit that gets your attention. So it turned out she had been John F. Kennedy’s nursemaid when he was 3 and 4 years old, and he used to fall asleep in her arms. She had a whole series of letters written from the president, and she wanted to get an offer. But the letters were too sentimentally valuable for her to ever let them go. So you can't appraise sentimental value. You can appraise monetary value. But often it's the sentimental value that's important.

Santoro: Ken Gloss can be found at the Brattle Book Shop on West Street in Boston, he can be seen on “Antiques Roadshow,” and this weekend you'll find him at the Boston International Antiquarian Book Fair at the Hynes Convention Center.