J chain is a polypeptide of molecular weight (Mr) approximately 15,000 common to human dimeric IgA and pentameric IgM. These immunoglobulin polymers show a high affinity for secretory component (SC) in vitro, a feature that, in some studies, has been claimed to be a function of the J chain. SC is a glycoprotein of Mr approximately 80,000 which is expressed on the basolateral surfaces of secretory epithelial cells where, according to a current hypothesis, it may act as a receptor for dimeric IgA and pentameric IgM which are selectively transported through secretory epithelial cells into exocrine fluids. Previous studies, however, have not excluded the possibility that secretory cells express isotype-specific Fc receptors for IgA and IgM which may be involved in epithelial transport. We now report that the adsorption of immunoglobulin polymers to SC-expressing epithelial cells depends solely on a J chain-determined binding site. This finding lends biological significance to the striking J-chain expression shown by immunoglobulin-producing immunocytes in secretory tissues.

Biological Transport↗

PubMedDate not supplied

Toxicity of oxygenated cholesterol derivatives toward cultured human umbilical vein endothelial cells.

Human umbilical vein endothelial cells were cultured in the presence of several oxygenated cholesterol derivatives that are known to affect the viability of other cell lines. 5-Cholestene-3 beta,7 beta-diol (7 beta-hydroxycholesterol) caused a time- and concentration-dependent perturbation of the endothelial cells. Exposure to 50 mumol/l of this compound for 18 hours resulted in marked contraction of the cells, followed by increasing cell detachment from the substrate and Trypan Blue uptake in detached cells. Concomitantly release of lactate dehydrogenase from the cells reached about 80% at 24 hours. The release of tissue plasminogen activator and tissue plasminogen activator inhibitor-1 antigens decreased at a concentration of 7 beta-hydroxycholesterol lower than that required for reducing general protein synthesis. 7 beta-Hydroxycholesterol at 50 mumol/l first increased the release and then (at 100 mumol/l) inhibited the synthesis of von Willebrand factor. Incubation with 100 mumol/l of 5-cholestene-3 beta, 7 alpha,22(R)-triol (7 alpha,22-dihydroxycholesterol)e and the isomeric 5-cholestene-3 beta, 7 beta, 22(R)-triol (7 beta, 22-dihydroxycholesterol) caused formation of intercellular gaps and some detachment of the cells after 24 hours. Cell injury was slightly more pronounced for the 7 alpha, 22-dihydroxycholesterol than for the 7 beta-isomer. Incubations with cholesterol under the same conditions gave no sign of cell injury.

Cells, Cultured↗

PubMedDate not supplied

Effect of alteration in triglyceride levels on factor VII-phospholipid complexes in plasma.

Clotting Factor VII activity emerges as a highly significant predictive factor for development of cardiovascular disease (CVD) in prospective trials. We have previously shown that in hypertriglyceridemic individuals a fraction of their clotting Factor VII molecules is present in an activated state in phospholipase C-sensitive complexes in plasma. These complexes may explain the increased Factor VII activity observed to be a predictive factor for CVD. We demonstrate here that the level of such complexes is amenable to dietary intervention and that the alteration in Factor VII complex levels correlates closely with the corresponding alteration in triglycerides.

Cardiovascular Diseases↗