An investigation was conducted to clarify the relationships of
IgA to the human liver. Immunocytochemical studies were performed on biopsy specimens from patients with
cirrhosis and
chronic hepatitis without any apparent history of
alcohol abuse. The results showed that 1) a large amount of
IgA is associated with the sinusoidal surface of hepatocytes, endothelial cells and Kupffer cells, 2) this
IgA contains J chain and can form a complex with
secretory component, and 3) this mainly belongs to the
IgA1 subclass, 4)
IgA in vesicles within hepatocytes and Kupffer cells is always associated with
acid phosphatase activity, and 5)
IgA containing vesicles within ductular epithelial cells always lack such
enzyme activity. We conclude that 1) the
IgA bound to the surface of hepatocytes, sinus endothelial cells and Kupffer cells is polymeric
IgA1 uncomplexed with SC, and 2) this
IgA occasionally enters these cells, and may be degraded in the lysosomes. 3)
Polymeric IgA combines with SC in the ductular epithelium and may be secreted into bile. These findings suggest that J chain-linked
polymeric IgA bound to the surface of hepatocytes and Kupffer cells has a certain pathological significance in
liver diseases and might be involved in the clearance of excess
IgA from the circulation.