May be involved in the maintenance of the mucosal structure as a gel-like component of the mucosa. Interacts with the Fc portion of IgG and with MUC2. Mainly expressed in placenta and colon epithelium. Expressed in thyroid, and down-regulated in thyroid carcinomas. Present in serum, with higher levels in patients with various autoimmune diseases (at protein level). The N-terminal IgGFc-binding region is primate-specific.