F13A1 and psoriasis: Mast cell degranulation can impact the activity of dermal dendrocytes, including those expressing factor XIIIa, by releasing various bioactive molecules.11,12 The induction of factor XIIIa+ dendrocytes by mast cell degranulation has been observed in certain skin diseases such as psoriasis,13 acute urticaria,12 and Kaposi sarcoma.14 Dendrocytes are present in the oral mucosa and a subset of these dendrocytes near blood vessels express the protransglutamine-clotting enzyme factor XIIIa.15,16 Factor XIIIa+ dendrocytes have been detected in reactive and neoplastic oral lesions.