IL1R1 and hemarthrosis: During the acute phase (day 3), all M1 markers were elevated in response to hemarthrosis (Il6, Il1β, Nos2, Cxcl2 and Il1r1), whereby Il6 and Nos2 were suppressed to baseline levels by rhFVIII and mFcFVIII alike, without effects on Il1β, Cxcl2 and Il1r1 (Fig 5C).