Albert L. Jones

The association of polypeptide hormones and growth factors with the nuclei of target cells

Abstract Nuclear sites of action have long been recognized for steroid and thyroid hormones. Evidence accumulated over the past decade suggests that polypeptide hormones and growth factors may also have nuclear sites of action.

Hepatocyte handling of immunoglobulin A in the rat: the role of microtubules.

Plasma-derived dimeric immunoglobulin A is transported through liver parenchymal cells into bile, in association with its glycoprotein receptor secretory component, by a vesicular transport system. This study was designed to determine the effects of colchicine, a microtubule-disrupting agent, and thus the role of microtubules on the uptake, intracellular transport, and subsequent biliary secretion of dimeric immunoglobulin A. In vivo studies in rats showed that colchicine treatment reduced the amount of intraportally injected 125I-dimeric immunoglobulin A that appeared in the bile. It was also found that although the livers in colchicine-treated animals could sequester and internalize immunoglobulin A, it was not readily secreted into bile. In vitro studies using peroxidase-labeled antisecretory component and 125I-dimeric immunoglobulin A autoradiography were both used to determine the site of this block in immunoglobulin A secretion. These studies demonstrate that colchicine disruption of microtubules (a) has little initial effect on the binding and internalization of dimeric immunoglobulin A; (b) has a major effect on the translocation of immunoglobulin A-containing vesicles within the hepatocyte, and (c) most likely prevents the translocation of newly synthesized secretory component to the plasma membrane.

The architecture of bile secretion

The liver, an organ essential to life, has a multitude of functions within the milieu of the organism. It has been the subject of extensive biochemical, physiological, and morphological research during the past century. However, the subcellular route of bile secretion, the primary topic of this review, remains, for the most part, an enigma. Webfer (1664) and Malpighi (1666) defined the livers functional units in terms of hepatic lobules. These early investigators provided evidence that the liver was the source of bite rotund in the gallbladder and small intestine. Now, 301)years later, with the develop/nent of transmission electron microscopy and tissue processing for high-resolution imaging, the subcellular structure of those cells which define the biliary spaces, namely the hepatocytes and the bile duct and gallbladder epithelia, have been elucidated. Much information has been accumulated about the origin, formation, turnover, function, and environmental adaptations of the organelles within these cells. Surprisingly, very little is known about the respective roles of hepatocyte ~organelles in the formation and secretion of bile. From the electron microscopists point of view, the lack of knowledge concerning this vital hepatic function is understandable since bile, a complex fluid, contains no components that are themselves electron dense or that are sufficiently insoluble to remain compartmentalized during tissue processing procedures employed in modern electron microscopy. Several inroads have recently been made, however, towards defining the

Semipurified dietary fiber and small-bowel morphology in rats.

Newly weaned rats fed 12 weeks on a diet containing no dietary fiber or no fiber except for 10% cellulose, maintained the leaf-like intestinal villous morphology present at weaning, as observed by scanning electron microscopy. In rats on a normal laboratory diet the jejunal morphology showed progression from the leaf-like villous pattern at weaning to broad-leafed, long-ridged villi of adulthood. Pectin added to a no-fiber diet caused structural changes similar to but less well developed than those changes in the rats on a standard diet. Striking differences were noted not only in the appearance of the intestinal villi but in the number of villi per square centimeter between those animals on no fiber or no fiber except cellulose and those animals on pectin or standard diets. Cholestyramine, a strong pharmacological bile salt-binding agent, when added to a nofiber diet, did not promote development of the usual villous pattern, and the structure remained the same as that in rats on no-fiber and cellulose diets. Cellulose (no bile salt-binding capability) and pectin (weak bile salt-binding capability) added to a no-fiber diet were associated with significant differences in the number of villi in both the jejunum and the ileum. The observed changes in morphology are unlikely to be due to differing bile salt-binding capabilities of different fiber substances.

Effect of Aging On the Hepatobiliary Transport of Dimeric Immunoglobulin-a in the Male Fischer Rat

Recent studies have suggested that the hepatobiliary transport of serum dimeric immunoglobulin A constitutes an important secretory route for this ligand. However, the information that is currently available has been accumulated from studies in young animals or in patients with liver disease. Aging is known to result in (a) reduced hepatobiliary function(s), (b) an increased incidence of gastrointestinal infectious diseases, and (c) a marked decline in the immune response. We evaluated the effect of aging on the in vivo hepatic capacity to transport dimeric immunoglobulin A from blood to bile. Young adult rats (3-4 mo) secreted 125I-labeled dimeric immunoglobulin A into the bile at a rate sixfold greater than that measured in either mature (12 mo) or senescent (24-25 mo) animals. This age-related decline appears to be relatively independent of bile flow and bile acid secretion. Quantitative light and electron microscopic autoradiographic evidence suggests that aging may impair the rate at which this ligand is translocated across the hepatocytes to the bile canaliculi.

Specific antibody synthesis and biliary secretion by the rat liver after intestinal immunization with cholera toxin

This study was designed to investigate the location, specificity, and significance of antibody-containing cells in the liver. After intestinal administration of cholera toxin, high numbers of specific antibody-containing cells appeared in the liver during the early priming period and after boosting. In contrast, a significant number of specific antibody-containing cells appeared in the lamina propria of the intestine only after boosting. In the liver, the specific antibody-containing cells were predominantly located in the sinusoidal region of zone 1 of the liver lobules. About 80% of the specific antibody-producing cells in the liver synthesized anticholera toxin antibody of the immunoglobulin A class. During the priming period, the concentration of immunoglobulin A anticholera toxin in bile paralleled the increase and decrease in the number of specific antibody-containing cells in the liver. Liver perfusion experiments indicated that during the priming period at least 70% of the biliary immunoglobulin A anticholera toxin antibody was synthesized within the liver, whereas 30% was synthesized in the liver after boosting. Thus, during the early immune response, the liver seems to be the major source for specific biliary antibody to intestinally administered cholera toxin.

Comparison of leukocytes obtained from the intestinal lumen of Giardia-infected immunocompetent mice and nude mice

Previous studies have suggested that Giardia infections are cleared immunologically, but have not defined the mechanism of clearance. The aim of the present work was to compare subpopulations of leukocytes harvested from the intestinal lumen of immunocompetent BALB/c mice, which clear Giardia muris infection rapidly, with those of immunodeficient nude mice, which become chronically infected with Giardia muris. Leukocytes were obtained from the intestinal lumen of Giardia-infected mice, and subpopulations of these cells were quantified after immunofluorescent staining with monoclonal antibodies. Identical numbers of leukocytes were harvested from the intestinal lumen of Giardia-infected immunocompetent mice and nude mice, but the number of these leukocytes bearing the T-lymphocyte antigen Thy-1.2 was smaller in nude mice than in immunocompetent mice. In contrast, no striking differences were observed between the numbers of luminal cytotoxic/suppressor T lymphocytes or macrophages in Giardia-infected nude versus immunocompetent mice. The findings suggest that clearance of Giardia muris infection is not mediated by cytotoxic T lymphocytes or macrophages. Subsequently, T lymphocytes and T-lymphocyte subsets were quantified in cell suspensions prepared from Peyers patches of immunocompetent BALB/c mice and nude mice. It was found that nude mice have a profound deficiency of Peyers patch helper/inducer T lymphocytes. This deficiency may account for the inability of nude mice to clear Giardia muris infection at a normal rate.

Immunoglobulin A receptor of rat small intestinal enterocytes is unaffected by aging

The receptor for polymeric immunoglobulins is responsible for the transport of immunoglobulin A (IgA) through epithelial cells and its subsequent delivery to mucosal surfaces. We have extended our previous studies of the IgA receptor in the liver of the aging Fischer rat to include the small intestine. Basolateral membrane-enriched fractions prepared from rat small intestinal enterocytes exhibit a single binding site for dimeric IgA. This receptor is specific for molecules that interact with rat secretory component, e.g., rat dimeric IgA and IgM and human polymeric IgA but not human monomeric IgA or rat secretory IgA. Inhibition of binding by rabbit-antirat secretory component also indicated that binding is specific for secretory component. Both liver and intestinal membranes showed virtually identical binding specificity. Membranes from crypt cells show increased IgA binding (320 fmol bound per milligram protein) compared with villous cells (105 fmol bound per milligram protein); however, other than increased binding, crypt cells show the same binding characteristics as villous cells. In contrast to our previous findings, in which liver plasma membranes from old rats showed a four-fold decrease in IgA binding compared with young adult rats, membrane fractions from rat enterocytes showed no alterations in dimeric IgA binding with increased age.

Harvesting of leukocytes from intestinal lumen in murine giardiasis and preliminary characterization of these cells

The aims of this study were to develop a method for harvesting leukocytes from the mouse small intestinal lumen and to identify leukocytes which enter the intestinal lumen of mice infected withGiardia muris. Giardia-infected and uninfectedBALB/c mice were anesthetized, and the small intestine was removed. The intestinal lumen was then flushed with nutrient medium, and the luminal washings were found to contain substantial numbers of mononuclear leukocytes. The number of these cells harvested from the intestinal lumen of 24 mice infected withGiardia muris was 22±3×104 (mean value ± standard error). Most of the cells were lymphocytes, although small numbers of macrophages were also obtained. By staining with monoclonal antibodies, approximately 50% of the intraluminal leukocytes were shown to be T lymphocytes. Similar numbers of mononuclear leukocytes were obtained from the intestinal lumen ofGiardia-infected and uninfected mice. However, T lymphocytes and other mononuclear cells from infected animals were frequently observed in contact withGiardia trophozoites. This observation is consistent with the hypothesis that intraluminal leukocytes play a part in gastrointestinal immune defense.

Immunology of the Gastrointestinal Tract and Liver

This book contains 11 chapters. Some of the chapter titles are: T cells and Other Non-B Lymphocytes; Mucosal Mast Cells and IgE; Genetic Aspects of Gastrointestinal Immunology; Immunological Functions of the Liver; Lymphocyte Migration and Mucosal Immunity; and Immunoglobulin Circulation and Secretion.