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Biomedical subjects

J M Osborne

Publications and source records attributed to J M Osborne.

At least 19 recordsLinked to original sources
PubMed2001

The Fc receptor for IgG expressed in the villus endothelium of human placenta is Fc gamma RIIb2.

To evaluate the potential role of human placental endothelial cells in the transport of IgG from maternal to fetal circulation, we studied Fc gamma receptor (Fc gamma R) expression by immunohistology and immunoblotting. Several pan-Fc gamma RII Abs that label the placental endothelium displayed a distribution pattern that correlated well with transport functions, being intense in the terminal villus and nil in the cord. In contrast, the MHC class 1-like IgG transporter, FcRn, and the classical Fc gamma RIIa were not expressed in transport-related endothelium of the placenta. Our inference, that Fc gamma RIIb was the likely receptor, we confirmed by analyzing purified placental villi, enriched in endothelium, by immunoblotting with a new Ab specific for the cytoplasmic tail of Fc gamma RIIb. These experiments showed that the Fc gamma RII expressed in villus endothelium was the b2 isoform whose cytoplasmic tail is known to include a phosphotyrosyl-based motif that inhibits a variety of immune responses. We suggest that this receptor is perfectly positioned to transport IgG although as well it may scavenge immune complexes.

Antibodies, Monoclonal↗
PubMed2001

What about the other breast? A review of a series of bilateral breast carcinomas.

The BreastScreen Queensland Brisbane Southside BreastScreen Service reports on a study of 10 cases of bilateral breast carcinomas from a total cancer population of 217 cases. All cases were patients of screening examinations that were recalled for a suspicious lesion in one breast. Two cases were mammographically suspicious of bilateral tumours. In eight cases, tumours were ultrasonically visible in both breasts and in two further cases, the suspicion of bilateral malignancy was raised by the presence of bilateral microcalcification. It is not the purpose of this paper to provide a statistical analysis of the occurrence of bilateral breast cancer. This is a radiological paper from a breast screening service reporting on findings that conventional wisdom may find unusual. The incidence of bilateral breast malignancy in the study was found to be somewhat higher than expected. These cases have been diagnosed by the utilization of a particularly high standard of ultrasound and mammography, performed and interpreted by diagnosticians possessing an elevated level of suspicion of the possible presence of a second primary lesion. It is therefore proposed that an increased rate of diagnosis of bilateral tumours is possible with an evolution of assessment protocols, combined with quality ultrasound and mammography.

Journal Article↗
PubMed1999

The SH2-containing 5'-inositol phosphatase (SHIP) is tyrosine phosphorylated after Fc gamma receptor clustering in monocytes.

Current models of Fc gamma R signal transduction in monocytes describe a molecular cascade that begins upon clustering of Fc gamma R with the phosphorylation of critical tyrosine residues in the cytoplasmic domains of Fc gamma RIIa or the gamma-chain subunit of Fc gamma RI and Fc gamma RIIIa. The cascade engages several other tyrosine-phosphorylated molecules, either enzymes or adapters, to manifest ultimately an array of biological responses, including phagocytosis, cell killing, secretion of a variety of inflammatory mediators, and activation. Continuing to assess systematically the molecules participating in the cascade, we have found that the SH2-containing 5'-inositol phosphatase (SHIP) is phosphorylated on tyrosine early and transiently after Fc gamma R clustering. This molecule in other systems, such as B cells and mast cells, mediates an inhibitory signal. We find that clustering of either Fc gamma RIIa or Fc gamma RI is effective in inducing SHIP phosphorylation, that SHIP binds in vitro to a phosphorylated immunoreceptor tyrosine-based activation motif, peptide from the cytoplasmic domain of Fc gamma RIIa in activation-independent fashion, although SHIP binding increases upon cell activation, and that Fc gamma RIIb and Fc gamma RIIc are not responsible for the observed SHIP phosphorylation. These findings prompt us to propose that SHIP inhibits Fc gamma R-mediated signal transduction by engaging immunoreceptor tyrosine-based activation motif-containing cytoplasmic domains of Fc gamma RIIa and Fc gamma RI-associated gamma-chain.

Enzymes, Immobilized↗
PubMed1998

Murine DEP-1, a receptor protein tyrosine phosphatase, is expressed in macrophages and is regulated by CSF-1 and LPS.

The spectrum of protein tyrosine phosphatases (PTPs) expressed in bone marrow-derived murine macrophages (BMMs) was examined using reverse transcriptase-polymerase chain reaction. Ten different PTP cDNAs were isolated and in this study we focus on mDEP-1, a type III receptor PTP. Three mDEP-1 transcripts were expressed in primary macrophages and macrophage cell lines and were induced during macrophage differentiation of M1 myeloid leukemia cells. A variant mRNA was identified that encodes an alternate carboxyl-terminus and 3' UTR. The expression of mDEP-1 was down-regulated by CSF-1 (macrophage colony-stimulating factor) and up-regulated by bacterial lipopolysaccharide, an important physiological regulator of macrophage function that opposes CSF-1 action. Whole mount in situ hybridization, and immunolocalization of the protein, confirmed that mDEP-1 is expressed by a subset of embryonic macrophages in the liver and mesenchyme. mDEP-1 was also detected in the eye and peripheral nervous system of the developing embryo. Attempts to express mDEP-1 constitutively in the macrophage cell line RAW264 were unsuccessful, with results suggesting that the gene product inhibits cell proliferation.

Amino Acid Sequence↗
PubMed1996

Isolation from human placenta of the IgG transporter, FcRn, and localization to the syncytiotrophoblast: implications for maternal-fetal antibody transport.

The IgG transporter responsible for ferrying maternal IgG across the human placenta to fetal circulation has not been identified, although the human homologue of the neonatal rat Fc receptor (FcRn), a heterodimer with pH-dependent IgG affinity, structurally similar to MHC Class I molecules, was recently proposed as a candidate. Affirming this hypothesis, we describe herein the specific copurification from human placenta of 46- and 14-kDa proteins by IgG affinity at acid pH. The larger protein, characterized by its amino acid sequence and by immunoblot, is the alpha-chain of human FcRn (hFcRn). The smaller is beta2-microglobulin. Their coisolation by ligand affinity suggests that they comprise the hFcRn heterodimer. Placenta sections stained immunohistochemically with anti-hFcRn alpha-chain peptide Abs show extensive expression of hFcRn in the syncytiotrophoblast and traces in the endothelium and other unidentified cells of the villus stroma. We find alpha-chain mRNA by Northern analysis in human placenta and in human trophoblast-like cell lines (JEG-3, ED27) but not in a human myelocytic cell line (HL60). We suggest that the placental hFcRn heterodimer may transport IgG to the fetus by a mechanism in which maternal IgG is pinocytosed nonspecifically and then carried to fetal tissues by a pH gradient from acidic endosomes to the pH-neutral basolateral surface of the syncytiotrophoblast. Furthermore, the known characteristics of FcRn suggest a wider function, that it is the receptor postulated by Brambell in the 1960s to regulate tissue and serum IgG concentrations by controlling IgG transport and catabolism.

Amino Acid Sequence↗
PubMed1996

The mechanism of platelet aggregation induced by HLA-related antibodies.

Immune-mediated platelet activation is emerging as an important pathogenic mechanism of thrombosis. In vitro studies have suggested two distinct pathways for immune-mediated platelet activation; one involving clustering of platelet Fc gamma RIIa, the other involving platelet-associated complement activation. HLA-related antibodies have been shown to cause platelet aggregation, but the mechanism has not been clarified. We evaluated the mechanism of platelet aggregation induced by HLA-related antibodies from nine patients. Antibody to platelet Fc gamma RIIa failed to block platelet aggregation with 8/9 samples, indicating that engagement of platelet Fc gamma RIIa is not necessary for the platelet aggregation induced by HLA-related antibodies. In contrast, platelet aggregation was blocked by antibodies to human C8 (5/7) or C9 (7/7). F(ab')2 fragments of patient IgG failed to induce platelet activation although they bound to HLA antigen on platelets. Intact patient IgG failed to aggregate washed platelets unless aged serum was added. The activating IgG could be adsorbed by incubation with lymphocytes and eluted from the lymphocytes. These results indicate that complement activation is involved in the aggregation response to HLA-related antibodies. This is the first demonstration of complement-mediated platelet aggregation by clinical samples. Five of the patients developed thrombocytopenia in relationship to blood transfusion and two patients developed acute thromboembolic disease, suggesting that these antibodies and the complement-dependent pathway of platelet aggregation may be of clinical significance.

Adult↗
PubMed1995

On the role of platelet Fc gamma RIIa phenotype in heparin-induced thrombocytopenia.

Heparin induced thrombocytopenia (HIT) is characterized by the formation of antibodies that activate normal donor platelets in vitro in the presence of heparin. We asked whether the commonly observed donor-specific variation in the platelet aggregation response to HIT antibodies is influenced by the density of Fc gamma RII on platelets or by the Arg/His 131 allelic polymorphism of platelet Fc gamma RII. We found that platelets with His/His 131 Fc gamma RII phenotype were unresponsive to HIT antibody (0/9) whereas platelets with the Arg/Arg 131 phenotype responded well (7/9). His/His 131 platelets were largely unresponsive also to a murine IgG1 antiplatelet monoclonal antibody (UR1) known to activate platelets by Fc gamma RII clustering. We then determined the frequency distribution of Fc gamma RIIa Arg/His 131 phenotypes on a series of 200 patients evaluated for HIT and 100 non-thrombocytopenic hospitalized patients. The frequency of the His/His 131 phenotype was significantly increased (34.4%) in the 96 thrombocytopenic patients with HIT antibody compared to the 104 thrombocytopenic patients without HIT antibody and the 100 non-thrombocytopenic patients (approximately 19%). Thus, the Fc gamma RII phenotype regulates the in vitro activation response of normal platelets to HIT antibody and is a risk factor for the thrombocytopenia of HIT.

Antibodies↗
PubMed1994

Clustering of the platelet Fc gamma receptor induces noncovalent association with the tyrosine kinase p72syk.

The Fc receptor for IgG in platelets was identified as the integral membrane isoform encoded by the Fc gamma RIIA gene. Functional analysis of this molecule determined that activated Fc gamma RIIA is tyrosine phosphorylated and that activation induced the physical association with the protein tyrosine kinase p72syk. Other tyrosine-phosphorylated molecules also co-immunoadsorbed with the activated receptor. Tyrosine kinase activity co-immunoadsorbing with the platelet Fc gamma R was enhanced upon activation and specifically induced the phosphorylation, on tyrosine residues, of a physically associated 72-kDa protein. These data support a model of Fc gamma receptor-mediated platelet activation where signal is transduced through inducible association of the tyrosine kinase p72syk with the low affinity Fc gamma receptor. Thrombin, a potent platelet agonist, has been shown to up-regulate the activity of the tyrosine kinase p72syk in platelets. Consequently, our findings identify a second pathway by which p72syk is activated in platelets.

Antigens, CD↗
PubMed1994

Ethnic variation in frequency of an allelic polymorphism of human Fc gamma RIIA determined with allele specific oligonucleotide probes.

We have genotyped 53 individuals from three ethnic groups (Japanese, Chinese, Asian Indian) for an allotypic polymorphism of a widely expressed low affinity Fc receptor for IgG (Fc gamma RIIA). The method, requiring PCR amplification of genomic DNA and Southern analysis with allele specific oligonucleotide probes, detects a single nucleotide difference (G or A) at base 494 which results in an arginine (R) or histidine (H) at amino acid 131 of the Fc gamma RIIA protein. This polymorphism has been shown to determine the affinity of the receptor for hIgG2; Fc gamma RIIA-H131 has a high affinity for hIgG2, while Fc gamma RIIA-R131 binds hIgG2 weakly. We found that the Japanese and Chinese groups have an increased frequency of the H/H131 allotype (61 and 50% respectively) as compared to the Caucasian group (23%), in agreement with previously reported phenotype data. The genotype distribution of the Asian Indian group was not different from our Caucasian group. The shifts in frequency of the R131 and H131 alleles in different populations may have implications for disease susceptibility when the hIgG2 antibody isotype predominates.

Alleles↗
PubMed1993

Insulin-like growth-factor binding protein (IGFBP) serum levels and hepatic IGFBP-2 and -3 mRNA expression in diabetic and insulin-treated swine (Sus scrofa).

1. Diabetes had no significant effect on IGFBP-3 message and serum levels however, subsequent insulin treatment caused more than a two-fold increase in both hepatic IGFBP-3 mRNA and serum levels above controls (P < 0.05). 2. The induction of diabetes in pigs significantly increased the steady state levels of IGFBP-2 mRNA in the liver of young swine (P < 0.05). 3. Both liver message and serum IGFBP-2 were reduced to control levels with insulin therapy. 4. We report here that in addition to its affects on IGFBP-2, insulin is involved in the regulation of IGFBP-3 expression.

Animals↗
PubMed1992

Insulin-like growth factor-I levels and gene expression in ovine hereditary chondrodysplasia (spider lamb syndrome).

Hereditary Chondrodysplasia or Spider Lamb Syndrome (SLS) is an inherited, semi-lethal, musculo-skeletal disease affecting lambs primarily of Suffolk or Hampshire breeding. Deformities of the limbs and spinal column along with multiple sites of ossification at the anconeal process are diagnostic for the disease. Muscle atrophy is also predominant. We have investigated the relationship between SLS and circulating levels of IGF-I and the IGF-BPs in older (50-80 d of age) animals. Serum IGF-I levels were lower (P less than 0.01) in SLS affected lambs (117 ng/ml) than in phenotypically normal lambs (188 ng/ml) while serum levels of the 32 kDa BP increased (P less than 0.01) 77% in SLS affected lambs as compared to contemporary controls. All other IGF-BPs appeared to be unaffected in this group. Gene expression of IGF-I and -II in the liver and muscle of younger (16-22 d of age) lambs was also measured. There were no differences in IGF-II expression in either muscle or liver between SLS affected and phenotypically normal control lambs. Muscle IGF-I expression also did not differ. However, liver IGF-I expression in SLS affected lambs was nearly double that of control lambs (P less than 0.01). These data suggest that the regulation of IGF-I and the IGF-BPs may be involved in the physical manifestations of this disorder.

3-Hydroxybutyric Acid↗
PubMed1991

Ultrastructural studies of the reaction of urate crystals with a cultured renal tubular cell line.

Hypotheses concerning the development of uric acid and gouty nephropathy suggest that the initiating disease mechanism involves an interaction between uric acid or monosodium urate monohydrate (MSUM) crystals and renal tubular epithelial cells. We have studied the interaction of these crystals with Madin-Darby canine kidney (MDCK) cells, which exhibit many of the characteristics of cells of the collecting duct epithelium. Addition of MSUM crystals to monolayer cultures of MDCK cells leads to the formation of reaction sites, localised areas which are raised above the monolayer forming a 3-dimensional structure. These reaction sites are evident within 4-8 h and appear to be initiated by the interaction of a single crystal or small number of crystals with a single cell. With time, both cells and crystals accumulate at the site. By 24 h most reaction sites involve 6-12 cells and numerous crystals. Interaction of MSUM crystals and MDCK cells not only involves the attachment of crystals to cells but, by 8 h, some crystals appear to be completely or partially covered by the cell membrane, and MDCK cells appear to react by growing around the crystals. Transmission electron microscopy shows that crystals are found not only within cells, but also within the intercellular spaces. Within the cells, crystals have been shown in vacuoles containing lysosomal enzymes, indicating the formation of a phagolysosome. Ultimately, enzyme release occurs. These studies support the hypothesis that some interstitial deposits of urate and uric acid in the kidney may be derived from intratubular deposits that react with the tubular epithelium and pass into the interstitium; loss of tubular integrity may not be a prerequisite for crystal migration.

Animals↗
PubMed1991

Effect of weaning at different ages on serum insulin-like growth factor I (IGF-I), IGF binding proteins and serum in vitro mitogenic activity in swine.

We investigated the effects of weaning or fasting of 21- or 35-d-old swine by monitoring serum mitogenic activity, circulating insulin-like growth factor I (IGF-I) and its binding proteins using L6 myoblast bioassays, RIA and ligand blotting techniques. Serum samples were collected from 21- or 35-d-old animals just before and 36 h after weaning or fasting. Sera from 21- and 35-d-old weaned animals were not significantly altered in their ability to promote myoblast proliferation, whereas sera from 21- and 35-d-old fasted animals caused 29 and 21% decreases (P less than .05) compared with preweaning. The mitogenic activity of control serum was inhibited by serum from fasted animals but not by preweaned or weaned sera. Serum IGF-I levels were decreased 65 to 70% (P less than .05) with weaning or fasting at both ages. Unoccupied binding sites on circulating IGF binding proteins in the 155 kDa range decreased 18 to 19% with weaning at both ages and decreased 40% (P less than .05) with fasting at 21 d but only 17% at 35 d. Ligand blotting revealed that the 43 and 39 kDa IGF binding protein bands decreased with weaning and fasting at both ages, whereas the 29-kDa band increased with weaning and fasting. These data indicate that serum IGF-I and specific IGF binding protein bands decrease during weaning or fasting at 21 and 35 d of age. However, serum mitogenic activity did not always follow serum IGF-I levels.

Age Factors↗
PubMed1991

The abnormal mammogram--what to do.

When an abnormality is detected in a mammogram the following questions should be answered: 1. Does a significant abnormality exist, that is, is the abnormality present in at least two views? 2. Should special imaging techniques, such as ultrasound, be used? 3. What is the conclusion of the radiologist? 4. Is the radiological abnormality clinically palpable? 5. Is the opinion of a breast specialist required? 6. Can fine needle aspirations cytology of the area be performed accurately and without trauma? 7. Should biopsy be undertaken? By posing these questions in sequence and obtaining firm answers, small cancers should not be missed and the biopsy rate will be kept to an acceptably low level.

Biopsy↗
PubMed1990

Reaction of MDCK cells to crystals of monosodium urate monohydrate and uric acid.

Madin-Darby canine kidney (MDCK) cells exhibit many of the characteristics of cells of the cortical collecting tubule. Since hypotheses concerning the development of gouty and uric acid nephropathy involve a reaction between such cells and crystals, either of monosodium urate monohydrate (MSUM) or uric acid, the reaction between MDCK cells in culture and the above crystals was studied, both morphologically and functionally. In monolayer cultures, reaction sites developed within four hours of exposure to urate crystals. These increased in number for up to 72 hours and subsided gradually after removal of the crystals. At these reaction sites, crystals were observed to have passed beneath the cell surface and could be demonstrated both within intra-cellular lysosomes as well as within the inter-cellular spaces. When the MDCK cells were maintained as single cells in suspension, phagocytosis of crystals by the majority of the cells could be observed, but the response was much more rapid than in monolayers. During the cell/crystal reaction, significant amounts of lysosomal enzymes and prostaglandin E2 were released and, to a less significant degree, cytosolic enzymes, presumably due to cell lysis. This enzyme release did not occur in MDCK cells grown in protein-free medium, and protein coating of the crystals was necessary for reactivity with cells. In this regard, coating with IgG or lysozyme was more effective than albumin. The reaction with uric acid crystals revealed a reactivity which was lesser in degree but qualitatively similar to that of urate crystals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Evaluation of the mammographic lesion.

Radiologists have all too often been vague about mammographic problems presenting on films. Their reports are often too equivocal. However, with a thorough mammographic evaluation, most lesions can be classified as benign, malignant or spurious. We have listed thirteen positions, apart from the routine craniocaudal and oblique views, that may help decide the malignant potential of a mammographic problem.

Breast Neoplasms↗