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B J Underdown

Publications and source records attributed to B J Underdown.

At least 73 records · Page 4Linked to original sources
PubMed1976

The relative paucity of IgE in human milk.

The levels of IgE were determined in paired samples of serum and milk when whey obtained 3 to 8 days of postpartum, from 16 human lactating mothers who had reported a history of allergy to a variety of common allergens. Two assay procedures were employed to measure total IgE, a double-antibody assay and a commercially available solid phase assay (RIST). In addition, each sample of serum and whey was tested for specific IgE antibodies to a variety of allergens by the RAST test. The levels of total serum IgE were between 30 and 2300 I.U./ml and relatively good agreement was observed for both the double-antibody and RIST methods. In contrast, total IgE levels in milk whey were either undetectable (less than 3.0 I.U./ml in 14 of 16 subjects) or very low when analyzed by the double-antibody method, but were very high (400 to 1650 I.U./ml when analyzed by the RIST method. However, IgE added to milk whey could be measured by the double-antibody procedure indicating that the low levels detected in milk were not a fault of the double-antibody assay. It was assumed that the RIST test was subject to nonspecific interference by factors in milk whey which caused the determination of high, but incorrect, levels of IgE. Specific IgE antibodies were detected in the serum of 10 of 16 subjects but were not present in milk whey. A comparison of the whey/serum ratios of albumin, IgA, and IgE suggested that little, if any, IgE is selectively synthesized or secreted in the mammary gland.

Animals↗
PubMed1975

A study of the association of human secretory component with IgA and IgM proteins.

Human secretory component (SC) was isolated from colostral whey, and the binding of 125I-SC to purified IgA and IgM monoclonal proteins was studied using two methods to separate free from immunoglobulin-bound 125I-SC: a) gel filtration on Sephadex G-200, and b) precipitation of 125I-SC-Ig complexes with anti-Ig antibody. Both IgA dimeric proteins and IgM pentamers bound 125I-SC with approximately one SC-binding site per mole of polymer and similar affinity. Assuming a reversible equilibrium, an apparent association constant congruent to 10-8 M-1 was calculated to govern the binding of 125I-SC to immunoglobulin polymers. The assignment of a single association constant may be an oversimplication, particularly for the case of IgA polymers, since evidence was obtained that disulfide bonds were formed in the 125I-SC-IgA complex. Despite the complexity of the reaction, binding of 125I-SC to both IgA and IgM polymers could be analyzed by standard methods of saturation analysis, and both were shown to have a similar affinity for 125I-SC. No differences were noted in the affinity of 125I-SC binding to the IgA1 and IgA2 subclasses. Binding of monomeric IgA and IgM proteins could not be measured and was at least 100-fold lower than that found for IgA and IgM polymers. Complexes of 125I-SC with IgA dimers were presumed to involve covalent bond formation, since these complexes did not dissociate in guanidine-HCl. One IgA2 trimer did not form a covalent bond since it was completely dissociated in guanidine. In contrast, 125I-SC-IgM complexes were dissociated in denaturing solvent, indicating that such complexes were held together primarily by non-covalent bonds. Experiments with (Fc)5 mu isolated by high temperature tryptic digestion of IgM showed that binding of 125I-SC was to the Fc region of IgM proteins. It was suggested that the binding of SC with similar affinity to both IgA and IgM polymers may be important in the biologic function of both these immunoglobulin classes.

Absorption↗
PubMedDate not supplied

The fate of polymeric and secretory immunoglobulin A after retrograde infusion into the common bile duct in rats.

In the rat, plasma IgA is rapidly endocytosed by hepatocytes and translocated to the bile via a receptor-mediated vesicular transport system which appears to remain intact even during cholestasis. During the latter phenomenon, there is an accumulation of secretory IgA (sIgA) in plasma. These data suggest that biliary IgA can be regurgitated into the plasma compartment. The present study was designed to determine the location and mechanism(s) by which this might occur. 125I-labeled human polymeric IgA (pIgA) or sIgA was infused retrograde into the rat common bile duct at a flow rate of 20 microliter per min (5 to 10 micrograms per min pIgA; 7 micrograms per min sIgA) over 1 hr. Blood and liver samples were collected 10, 30 and 60 min, and radioactivity determined. Radioactive label appeared in the blood by 10 min and increased linearly with time. By 30 min, however, the liver had reached saturation. All of the label found in the blood was intact starting material, i.e., pIgA or sIgA. Electron microscopic autoradiography analysis clearly demonstrated the presence of grains in vesicles in hepatocyte pericanalicular cytoplasm, as well as in vesicles near the sinusoidal plasma membrane. No grains were observed associated with bile duct or ductule epithelium at any time period. Further, there was no grain accumulation near the parenchymal cell intercellular spaces indicating that paracellular flow plays little or no role in large protein regurgitation. In addition, by 60 min, there were grains associated with Kupffer cells. These data provide the first evidence that hepatocytes, during times of elevated biliary pressure can readily transport macromolecules from bile to plasma via nonreceptor-mediated membrane-limited vesicles.

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