We recently showed that development of SpA in SKG mice is associated with increased IL-33 production in the inflamed paws and small intestine (Regan-Komito et al., 2020), and others have found IL-33 is increased in the serum of patients with ankylosing spondylitis (Han et al., 2011; Li et al., 2013), the most common form of SpA in people. Here, IL33 is linked to ankylosing spondylitis.