Weak Fragment Crystallizable (Fc) Domain Interactions Drive the Dynamic Assembly of IgG Oligomers upon Antigen Recognition

Activation of membrane receptors through clustering is a common mechanism found in various biological systems. Spatial proximity of receptors may be transduced across the membrane to initiate signaling pathways or alternatively be recognized by peripheral proteins or immune cells to trigger external effector functions. Here we show how specific immunoglobulin G (IgG) binding induces clustering of monomeric target molecules in lipid membranes through Fc-Fc interactions. We visualize and characterize the dynamic IgG oligomerization process and the molecular interactions involved using high-speed atomic force microscopy, single-molecule force spectroscopy, and quartz crystal microbalance experiments. We found that the Fc-Fc interaction strength is precisely tuned to be weak enough to prevent IgG oligomerization in solution at physiological titers, but enabling IgG oligomerization when Fabs additionally bind to their cognate surface epitopes, a mechanism that ultimately targets IgG-mediated effector functions such as classical complement activation to antigenic membranes.

Unraveling the Macromolecular Pathways of IgG Oligomerization and Complement Activation on Antigenic Surfaces

IgG antibodies play a central role in protection against pathogens by their ability to alert and activate the innate immune system. Here, we show that IgGs assemble into oligomers on antigenic surfaces through an ordered, Fc domain-mediated process that can be modulated by protein engineering. Using high-speed atomic force microscopy, we unraveled the molecular events of IgG oligomer formation on surfaces. IgG molecules were recruited from solution although assembly of monovalently binding molecules also occurred through lateral diffusion. Monomers were observed to assemble into hexamers with all intermediates detected, but in which only hexamers bound C1. Functional characterization of oligomers on cells also demonstrated that C1 binding to IgG hexamers was a prerequisite for maximal activation, whereas tetramers, trimers, and dimers were mostly inactive. We present a dynamic IgG oligomerization model, which provides a framework for exploiting the macromolecular assembly of IgGs on surfaces for tool, immunotherapy, and vaccine design.

Retinol Dehydrogenase-10 Regulates Pancreas Organogenesis and Endocrine Cell Differentiation via Paracrine Retinoic Acid Signaling

Vitamin A-derived retinoic acid (RA) signals are critical for the development of several organs, including the pancreas. However, the tissue-specific control of RA synthesis in organ and cell lineage development has only poorly been addressed in vivo. Here, we show that retinol dehydrogenase-10 (Rdh10), a key enzyme in embryonic RA production, has important functions in pancreas organogenesis and endocrine cell differentiation. Rdh10 was expressed in the developing pancreas epithelium and surrounding mesenchyme. Rdh10 null mutant mouse embryos exhibited dorsal pancreas agenesis and a hypoplastic ventral pancreas with retarded tubulogenesis and branching. Conditional disruption of Rdh10 from the endoderm caused increased mortality, reduced body weight, and lowered blood glucose levels after birth. Endodermal Rdh10 deficiency led to a smaller dorsal pancreas with a reduced density of early glucagon⁺ and insulin⁺ cells. During the secondary transition, the reduction of Neurogenin3⁺ endocrine progenitors in the mutant dorsal pancreas accounted for fewer α- and β-cells. Changes in the expression of α- and β-cell-specific transcription factors indicated that Rdh10 might also participate in the terminal differentiation of endocrine cells. Together, our results highlight the importance of both mesenchymal and epithelial Rdh10 for pancreogenesis and the first wave of endocrine cell differentiation. We further propose a model in which the Rdh10-expressing exocrine tissue acts as an essential source of RA signals in the second wave of endocrine cell differentiation.

SU-E-T-236: Brachytherapy for Breast Cancer Patients with Implanted Pacemeker, Using Multi Lumen Partial Breast Applicator

PURPOSE

Discuss optimised Accelerated Partial Breast Irradiation (APBI) using a Strut-Adjused Volume Implant (SAVI) applicator for patients with implanted pacemeker, without overdosing or relocating the pacemaker.

METHODS

A right breast cancer patient with an in situ pacemaker (Medtronic model ADDR01) on the right side underwent breast conservative surgery and was referred for Partial Breast Irradiation (PBI) using Ir-192 High Dose Rate Brachytherapy. Preliminary estimation of the pacemaker dose from a pre-insertion CT study was about 8 % of the prescribed dose which exceeded the generally accepted dose of 2Gy. The challenge was to use a suitable applicator to treat the tumor bed and 1cm margin without exceeding the 2Gy limit to the pacemaker and the leads. A seven catheter SAVI device was selected and implanted in the right breast in an optimal direction and a 3D treatment plan was generated following a post insertion CT scan, using the Oncentra Brachy treatment planning system. Optimization tools namely anatomy based Inverse Planning Simulated Annealing (IPSA), and graphical optimization were utilized to load and optimize the dwell time in the catheters and reduce the dose received by the pacemaker. Device interrogation was conducted before and after the treatment. All operational parameters of the pacemaker were found to be normal.No change in the baseline reference values were observed.

RESULTS

Using the SAVI device it was possible to limit the pacemaker/ leads dose to less than 2 Gy. Target V100, V95 and V90 were 90.1%, 95.5% and 98.5% respectively. V150 and V200 being 18.6cc and 10.6cc respectively.Calculated average point doses on pacemaker assembly for ten fractions was 140cGy.

CONCLUSIONS

By combining the optimization tools of today's Brachytherapy planning system and a multilumen SAVI applicator, HDR partial breast irradiation can be safely delivered for breast cancer patients with in situ pacemaker, with out the fear of interrupting pacemaker functionality.

Angiostatin suppresses malignant glioma growth in vivo

Human malignant gliomas are among the most malignant and most intensely vascularized solid tumors. Angiostatin, an internal fragment of plasminogen, was recently discovered as an endogenous inhibitor of tumor-related angiogenesis by selective inhibition of endothelial cell growth. Using xenograft transplants of rat and primary human glioma cells in immunodeficient mice we investigated the effects of systemic administration of angiostatin purified from human plasma on tumor growth. The rat C6 and 9L glioma and the human U87 glioma cell lines implanted either s.c. or intracranially in Swiss nude mice responded to angiostatin in a dose-dependent fashion with growth inhibition to 11% of controls (P < 0.01), without detectable signs of toxicity. The inhibition of treated tumors was accompanied by a marked reduction of vascularity to 38% of controls (P < 0.01) in the presence of an up to 6-fold increased apoptotic index (P < 0.01), consistent with the hypothesis that angiostatin acts tumoristatic by inhibiting tumor-induced endothelial cell proliferation. Expression analysis of growth factors in angiostatin-treated tumors revealed an up to 3-fold decrease in vascular endothelial growth factor-mRNA and an up to 4-fold increase in basic fibroblast growth factor-mRNA, as compared with untreated controls in rat gliomas (P < 0.01). This suggests that inhibition of the tumorigenic phenotype may be mediated in part by a downregulation of vascular endothelial growth factor expression within the tumor. Our data demonstrate that systemic administration of angiostatin efficiently suppresses malignant glioma growth in vivo. The tumoristatic activity against intracranial tumors independent of the blood brain barrier suggests that targeting the vascular compartment may offer novel therapeutic strategies against malignant gliomas.

RXR agonists activate PPARalpha-inducible genes, lower triglycerides, and raise HDL levels in vivo

Peroxisome proliferator-activated receptors (PPARs) and retinoid X receptors (RXRs) are members of the intracellular receptor superfamily. PPARs bind to peroxisome proliferator-response elements (PPREs) as heterodimers with RXR and as such activate gene transcription in response to activators. Fibrates like gemfibrozil are well-known PPARalpha activators and are used in the treatment of hyperlipidemia. We show that the RXR ligand LGD1069 (Targretin), like gemfibrozil, can activate the PPARalpha/RXR signal-transduction pathway, including transactivation of the bifunctional enzyme or acyl-CoA oxidase response elements in a cotransfection assay. The activation also occurs in vivo, whereby in rats treated with LGD1069 or gemfibrozil, bifunctional enzyme and acyl-CoA oxidase RNA are induced and the combination of LGD1069 and gemfibrozil leads to a greater induction. Importantly, in hypertriglyceridemic db/db mice treated with RXR or PPARalpha agonists, triglyceride levels are lowered, and the combination again has significantly greater efficacy. RXR agonists also raise HDL cholesterol levels without changing apoA-I RNA expression. This observation suggests the use of RXR-selective agonists, "rexinoids," either alone or in combination with a fibrate as a new therapeutic approach to treating patients with high triglyceride and low HDL cholesterol levels.

[Extra-amniotic pregnancy. Diagnosis with transvaginal color Doppler]

We report on the early diagnosis of two cases of extraamniotic pregnancy in the first trimester using transvaginal colour Doppler. The flow alterations in trophoblastic and corpus luteum vessels were of low diagnostic significance.

Environmental and occupational health education: a survey of community health nurses' need for educational programs

1. Community health nurses address a wide variety of environmental issues, including problems with air and water quality, hazardous waste, and pesticide exposure. 2. Many community health nurses do not feel competent in identifying resources among health professionals and regulatory agencies to address environmental health issues. 3. Most community health nurses (79%) are interested in learning more about environmental health issues, with continuing education as the preferred format. 4. Major conceptual areas of occupational health and environmental health overlap, and qualified occupational health nurses may serve as resources in these particular areas.

Immunological effects of insulin-like growth factor-I--enhancement of immunoglobulin synthesis

In addition to its activity as a metabolic hormone and a regulator of somatic growth, insulin-like growth factor-I (IGF-I) has cytokine-like activities on lymphoid cells. A 14-day infusion of recombinant human (rh)IGF-I increased lymphocyte numbers in all the peripheral lymphoid organs examined. This increase was apparent for up to 3 weeks following cessation of hormone treatment. A second administration of rhIGF-I, given when the lymphocyte numbers in the rhIGF-I-treated mice had returned to control values, resulted in similar increases in the peripheral T and B cell populations. This increase in lymphocyte numbers had functional significance, since rhIGF-I-treated mice produced elevated antibody titres following primary or secondary antigen challenge compared with controls. In addition, when rhIGF-I-treated mice were immunized with a suboptimal dose of antigen they produced antibody titres which were equivalent to those generated by immunization with optimal doses of antigen. When examined in vitro, addition of rhIGF-I alone to cultures of splenocytes from antigen-primed mice stimulated immunoglobulin synthesis. These studies suggest that IGF-I produced locally by thymic and bone marrow stromal cells may be a natural component of B and T cell lymphopoiesis.

Insulin-like growth factor-1 stimulation of lymphopoiesis

We show that treatment of adult mice with recombinant human insulin-like growth factor 1 (rhIGF-1) induces striking modifications in lymphocyte number and function. 9-mo-old male mice received rhIGF-1 (4 mg/kg per d) or its excipient by subcutaneous infusion from osmotic minipumps for 7 or 14 d. Mice were weighed daily and bled at sacrifice; the spleen and thymus were harvested and single cell suspensions were made for analysis of cell phenotype and cell number. The responses of splenocytes to mitogens (concanavalin A, lipopolysaccharide, and pokeweed mitogen), alloantigens and dinitrophenyl ovalbumin were measured. After either 7 or 14 d of treatment, rhIGF-1 had an overall whole-body anabolic effect, resulting in increased body and organ weights with prominent increases in the weight of the spleen and thymus. Furthermore, the rhIGF-1 treated mice were normoglycemic but had reduced blood urea nitrogens, again reflecting the anabolic activity of rhIGF-1. The increased spleen and thymus weights were associated with a large increase in the number of lymphocytes in both organs. In addition to an increase in T cells, specifically CD4+ T cells, a dramatic increase in splenic B cells was also observed. This increase was accompanied by an enhanced responsiveness to dinitrophenyl ovalbumin resulting in increased immunoglobulin production. However, despite the increases in cellularity, there was a decrease in the in vitro responses of spleen cells to mitogens after 7 d of rhIGF-1 treatment. In contrast, treatment with rhIGF-1 for 14 d increased both the cell number and mitogenic responses of splenocytes suggesting that some time is required for the cells populating the peripheral organs to gain mitogenic responsiveness. It is clear from these data that rhIGF-1, at doses that have whole-body anabolic activity, can expand cell number in lymphoid tissue in a normal adult mouse. These dual effects of rhIGF-1, of increasing lymphocyte number and activity, indicate that, in a normal adult animal, rhIGF-1 can cause major changes in lymphoid tissues that are of potential benefit to the functioning of the immune system.

Studies on the renal transport of trimethylpentanoic acid metabolites of 2,2,4-trimethylpentane in rat renal cortical slices

2,2,4-Trimethylpentane (TMP), a nephrotoxic component of unleaded gasoline in male but not female rats, undergoes oxidative metabolism to yield 2,2,4- and 2,4,4-trimethylpentanol, pentanoic acid and 5-hydroxypentanoic acid. We have examined the effect of three of these pentanoic acid metabolites on the renal transport of the organic anion p-aminohippurate (PAH) and the organic cation tetraethylammonium (TEA) in renal cortical slices from male Fischer 344 rats. 2,4,4-Trimethylpentanoic acid, the major urinary metabolite in rats, produced a selective decrease in the accumulation of PAH without affecting TEA accumulation. Kinetic analysis showed that 2,4,4-trimethylpentanoic acid was a competitive inhibitor of the organic anion transport system, with a Ki of 4 mM. 2,4,4-Trimethyl-5-hydroxypentanoic acid also showed selective inhibition of PAH transport, while 2,2,4-trimethylpentanoic acid was less selective and reduced both PAH and TEA transport. Additional studies with radiolabeled 2,4,4-trimethylpentanoic acid showed that there was a time- and concentration-dependent accumulation of radioactivity into slices of renal cortex. However, experiments conducted at 4 degrees C and studies with metabolic inhibitors, or with an inhibitor of organic anion transport, indicated that little of the accumulated material was entering the cell. We conclude from these studies that the pentanoic acid metabolites formed from 2,2,4-trimethylpentane are not actively transported by the renal organic anion transport system. In summary, in vitro the pentanoic acid metabolites appear to bind to renal cortical tissue and thereby reduce the transport of PAH.

[Hysterosalpingography: synechiae? Gartner's ducts?]

A linear shadow parallel to the uterus longitudinal axis, was observed in a hysterosalpingography (HSG) and has set up a controversy between synechiae and Gartner's ducts, without reaching a definitive conclusion. A case like this does not seem to have been published previously.

Involvement of reversible binding to alpha 2u-globulin in 1,4-dichlorobenzene-induced nephrotoxicity

Similarly to unleaded gasoline, 1,4-dichlorobenzene (1,4-DCB) administered for 2 years caused a dose-related increase in the incidence of renal tumors in male but not in female rats or in either sex of mice. Unleaded gasoline and 2,2,4-trimethylpentane (TMP), a component of unleaded gasoline, increased protein droplet formation and cell proliferation in male but not in female rat kidneys. These protein droplets contained, alpha 2u-globulin, a male rat-specific low-molecular-weight protein and 2,4,4-trimethyl-2-pentanol, a metabolite of TMP that was reversibly bound to this protein. Studies were undertaken to determine if 1,4-DCB produced similar effects; 1,2-DCB was used for comparison since it did not produce renal carcinogenesis in male rats. Gel filtration chromatography of a 116,000g supernatant prepared from kidneys of 1,4-[14C]DCB-treated rats showed that radiolabel coeluted with alpha 2u-globulin as one sharp peak as opposed to a multipeak pattern observed for 1,2-[14C]DCB; the maximal quantity of radiolabel for 1,4-DCB was twice that for 1,2-DCB. Equilibrium dialysis of kidney cytosol in the presence or absence of sodium dodecyl sulfate demonstrated that the radiolabel was reversibly bound to alpha 2u-globulin; the amount for 1,4-[14C]DCB-treated rats was almost twice as much as that for 1,2-[14C]DCB-treated rats. 1,2-DCB was also shown to be covalently bound to renal alpha 2u-globulin, and covalently bound to liver and plasma high-molecular-weight proteins. 1,4-DCB and, to a minor extent, 2,5-dichlorophenol, the major metabolite of 1,4-DCB, were reversibly bound to renal alpha 2u-globulin from 1,4-DCB-treated rats. 1,4-DCB increased protein droplet formation in male but not in female rat kidneys, whereas equimolar doses of 1,2-DCB showed no effect in either sex. Renal cell proliferation, measured by [3H]thymidine incorporation into renal DNA, was increased after 1,4-DCB but not after 1,2-DCB treatment. Nephrotoxicity and biochemical alterations induced by 1,4-DCB resemble those of unleaded gasoline and suggest that a similar mechanism is involved in the induction of alpha 2u-globulin nephropathy in male rats.

The comparative pathobiology of alpha 2u-globulin nephropathy

alpha 2u-Globulin nephropathy is an important toxicologic syndrome that occurs in male rats following exposure to a number of important industrial and environmental chemicals. A low, but significant incidence of renal neoplasia develops in male rats as a chronic sequela to the disease. Studies on the pathogenesis of alpha 2u-globulin nephropathy have demonstrated that this protein is produced in large amounts in the male rat, that reversible binding occurs between chemicals and/or their metabolites and alpha 2u-globulin, and that this complex is resistant to proteolytic hydrolysis, leading to accumulation in renal lysosomes and subsequent cytotoxicity and cell death. This results in marked exposure-related increases in cell proliferation that persist for at least one year, providing exposure continues. This sustained increase in renal cell proliferation can promote initiated cells to form preneoplastic foci and renal neoplasia in male rats. Since this syndrome is highly species and sex specific, it is important to determine the relevance of these data for human risk assessment. The scientific considerations involved in high to low dose and species to species extrapolation are discussed.

2,2,4-Trimethylpentane-induced nephrotoxicity. I. Metabolic disposition of TMP in male and female Fischer 344 rats

2,2,4-Trimethylpentane (TMP), a component of unleaded gasoline, causes nephrotoxicity in male, but not in female, rats. In the present study, male and female Fischer 344 rats were treated with a single oral dose of [14C]TMP (4.4 mmol/kg; 2 microCi/mmol). Radiolabeled material in kidney, liver, and plasma was determined at 4, 8, 12, 24, and 48 hr after dosing. Maximum concentration of TMP-derived radioactivity in kidney, liver, and plasma of male rats was found after 12 hr (1252, 1000, and 403 nmol eq/g, respectively), whereas those measured in females were found after 8 hr (577, 1163, and 317 nmol eq/g, respectively). A selective retention of the TMP-derived radiolabel in the kidneys of male rats was noted when peak tissue concentration was expressed as a percentage of administered dose. Kidney concentrations of TMP-derived radiolabel increased in a nonlinear, but dose-dependent, manner; the kidney to plasma ratio was greater at low doses than at higher doses. Increased retention of radiolabel material in the kidney was associated with a significant increase in renal concentration of the male-rat-specific protein, alpha 2u-globulin, 24 and 48 hr after TMP administration. Total radioactivity collected in urine 48 hr after TMP administration was similar in males and females (32 and 31% of dose). Identification and quantitation of the urinary metabolites of TMP showed that both male and female rats metabolize TMP via the same pathway and at a similar rate. Female rats, however, excreted more conjugates of 2,4,4-trimethyl-2-pentanol in urine than males. 2,4,4-Trimethyl-2-pentanol was the major metabolite present in the male rat kidney, but was absent in the female rat kidney. The renal retention of 2,4,4-trimethyl-2-pentanol appears to account for the delayed clearance observed in the disposition of [14C]TMP-derived radiolabel. Based on the concomitant accumulations in renal alpha 2u-globulin concentration and renal 2,4,4-trimethyl-2-pentanol concentration, an association is speculated between these two components. The male-rat-specific accumulation of 2,4,4-trimethyl-2-pentanol may therefore reflect the accumulation of a "metabolite-alpha 2u-globulin" complex. This may be relevant to the male-rat-specific nephrotoxicity produced by TMP.

2,2,4-Trimethylpentane-induced nephrotoxicity. II. The reversible binding of a TMP metabolite to a renal protein fraction containing alpha 2u-globulin

Trimethylpentane (TMP) produces nephrotoxicity in male but not in female rats. The toxicity is characterized by an increase in protein droplets in proximal convoluted tubular cells and an increase in the renal concentration of the male-rat-specific protein alpha 2u-globulin. Subcellular fractionation of the kidneys from male rats 24 hr after [3H]TMP administration showed that about 60% of the radiolabeled material was localized in the 116,000g supernatant. Column chromatography of this supernatant resolved the radioactivity into two components; one, which contained about 26% of the radiolabel, coeluted with alpha 2u-globulin and cross-reacted with an antibody specific for alpha 2u-globulin. The remaining component eluted in the low-molecular-weight range (less than 1000 Da) and was assumed to be TMP metabolites. Radiolabel from [3H]TMP in male rat urine also resolved into two components with about 0.1% of the radiolabel in urine coeluting with the alpha 2u-globulin-containing fraction. Radiolabel from TMP in male rat liver 116,000g supernatant and plasma and in female rat kidney 116,000g supernatant eluted as a single component in the low-molecular-weight range. Dialysis (1000-Da cutoff) of male kidney 116,000g supernatant led to a loss of the low-molecular-weight components, but nondialyzable radiolabel (about 20%) still coeluted with the alpha 2u-globulin after gel chromatography. Dialysis against 0.1% sodium dodecyl sulfate led to a loss of both the low- and high-molecular-weight radioactive material. These results suggested that the high-molecular-weight radioactive material was formed by the reversible binding of a radioactive component of TMP to a male-rat-specific protein. Gas chromatography-mass spectrometry of an ethyl acetate extract of the alpha 2u-globulin-containing fractions of TMP-treated male rat kidney 116,000g supernatant identified 2,4,4-trimethyl-2-pentanol as the only bound metabolite to alpha 2u-globulin. These studies provide the first evidence for a reversible binding between a metabolite of TMP and a male-rat-specific protein in the kidney and thus provide important insight delineating a potential mechanism of hydrocarbon-induced hyaline-droplet nephropathy.

A Bacillus subtilis plasmid that can be packaged as single-stranded DNA in Escherichia coli: use for oligodeoxynucleotide-directed mutagenesis

A Bacillus subtilis/Escherichia coli shuttle vector was modified to contain the origin of DNA replication of the E. coli filamentous phage f1, in both orientations. Upon superinfection with and f1-related phage of an E. coli strain containing either of the modified vectors, the single-stranded (ss) form of the plasmid was packaged in virions and released to the culture medium. Each of these ss DNAs has been purified from the virions and used as a template for oligodeoxynucleotide-directed mutagenesis. The resulting mutations were demonstrated by DNA sequencing. The capacity of these vectors to be isolated as phage ss DNA from E. coli and to replicate as plasmids in B. subtilis makes them convenient substrates for the production of oligodeoxynucleotide-directed mutations for studies in B. subtilis.