Secretor piece

IgA is associated mainly with seromucous secretions such as saliva, tears, nasal fluids, etc., and is secreted as a dimer with both a J chain and a secretor piece (relative molecular mass 70 000), the latter apparently to prevent damage to the molecule by proteolytic enzymes. Its major role appears to be the protection of mucous membranes and its presence in blood, mainly as the monomer, may be as a result of absorption of the degraded dimer. 

The 7 S IgA monomer released from cells under mucosae seems to be largely taken up by the epithelial cells, where it is dimerized and a secretor piece is added prior to its active secretion as 11 S secretory IgA (see Fig. 5). That secretion is active is evidenced by an apparent IgA clearance (across the membrane) some thirty times higher than for albumin, a smaller molecule (H12). 

---

See also in sourсe #XX -- [ ]

---