Disulfide bond formation between dimeric immunoglobulin A and the polymeric immunoglobulin receptor during hepatic transcytosis

Abstract

The polymeric immunoglobulin receptor on rat hepatocytes binds dimeric IgA on the sinusoidal surface and mediates its transport to the canaliculus, where the complex of dimeric IgA and secretory component, the cleaved extracellular domain of polymeric immunoglobulin receptor, is secreted into bile. This process is unique in that disulfide bonds are formed between dimeric IgA and polymeric immunoglobulin receptor during transcytosis, permanently preventing their dissociation. Here we present three lines of evidence that disulfide bonding between dimeric IgA and polymeric immunoglobulin receptor occurs predominantly in a late transcytotic compartment and that hepatic transcytosis can proceed in the absence of disulfide bond formation. First, throughout the course of transcytosis the percentage of intracellular dimeric IgA disulfide bonded to polymeric immunoglobulin receptor is less than half that in bile, suggesting that disulfide bond formation is a late event in transcytosis. Second, dimeric IgA that recycles from early endocytotic compartments into the circulation is mostly noncovalently bound to secretory component. Finally, the rate of transcytosis of dimeric IgA and its appearance in bile are not affected when disulfide bond formation with polymeric immunoglobulin receptor is inhibited by blocking of free thiol groups on dimeric IgA with iodoacetamide. These results are consistent with other findings in the literature and indicate that the main physiological role of disulfide bond formation between dimeric IgA and polymeric immunoglobulin receptor is not to facilitate transcytosis but, rather, to stabilize the dimeric IgA-secretory component complex after its release into external secretions such as bile and intestinal secretions.

Production of secretory immunoglobulin A by a single mammalian cell

“…The assembly of sIgA in the transfected myeloma cells appears to take place in the Golgi apparatus when dIgA and SC are present together. When culture supernatant from a transfectant was concentrated 100-fold and analyzed by gel filtration on two Superose 6 columns (Pharmacia) in series (19), three overlapping peaks with retention volumes of 27.5, 29.5, and 33 ml were observed ( Fig. 2A).…”

The polymeric immunoglobulin receptor: structure and synthesis

“…We observed that disulphide bonding between pIgR and IgA in rat liver occurs late in the transcytotic pathway [18]. Furthermore, normal transcytosis of the pIgR-pIgA complex can occur both in vivo and in cultured cells under conditions where disulphide bonding is prevented [18,19]. We therefore favour the hypothesis that the significance of disulphide bonding between pIgR and pIgA is not to facilitate transcytosis, but rather to prevent dissociation of the secretory IgA complex in the often harsh milieu of external secretions.…”

“…Given the conserved positions of the critical cysteine residues, it is assumed that the same process is responsible for disulphide bonding between pIgR and pIgA in non-human species. We observed that disulphide bonding between pIgR and IgA in rat liver occurs late in the transcytotic pathway [18]. Furthermore, normal transcytosis of the pIgR-pIgA complex can occur both in vivo and in cultured cells under conditions where disulphide bonding is prevented [18,19].…”

Structural Requirements for Polymeric Immunoglobulin Assembly and Association with J Chain

“…The assembly of dimeric IgA is initiated with the formation of H 2 L 2 monomer units through a pathway in which H ϩ L 3 HL 3 H 2 L 2 (8). The penultimate cysteine in the tail-piece of one ␣ chain forms a disulfide bond with J chain, which in turn forms a disulfide bond with the ␣ chain of a second monomeric subunit (5, 9 -11).…”