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Biomedical subjects

A M Collins

Publications and source records attributed to A M Collins.

At least 37 records · Page 2Linked to original sources
PubMed1999

A role for the hepatobiliary system in IgE-mediated intestinal inflammation in the rat.

BACKGROUND: For many years the central focus of research into gastrointestinal hypersensitivity reactions has been the mast cell population of the intestinal lamina propria. Since bile is known to deliver immunological mediators to the gastrointestinal tract, the possibility arises that extra-intestinal populations of mast cells may also contribute to IgE-mediated intestinal damage. OBJECTIVES: To characterize hepatic mast cells in the rat and to investigate the role of the hepatobiliary system in a model of IgE-mediated reactivity to dietary antigen. METHODS: Wistar rats were passively sensitized with monoclonal antidinitrophenyl (DNP) IgE antibodies, and were later challenged orogastrically with DNP-HSA. Additional animals were sensitized, then bile duct-cannulated prior to antigen challenge. At various time points, liver and intestinal samples were collected for histological examination, and bile was collected and assayed for histamine and TNFalpha. RESULTS: Hepatic mast cells display a mucosal mast cell-like phenotype, and are closely associated with the vessels of the portal triads. Orogastric antigen challenge led to a rapid and significant decline (P<0.0001) in detectable mast cells as a result of anaphylactic degranulation. The median number of granulated mast cells associated with each portal triad in liver sections declined from six per portal triad to one per portal triad post-antigen challenge. After 15 min, biliary histamine concentrations rose above background levels (P<0.01). TNFalpha was also detectable in the majority (4/6) of bile samples within 15 min of challenge. Histological examination of the gastrointestinal mucosa revealed disruption to the villous epithelium ranging from oedematous changes to gross destruction. Such damage was not seen in animals in which bile had been externally drained. CONCLUSION: The data indicate that biliary products are major contributors to the gastrointestinal damage arising from IgE-mediated hypersensitivity reactions in the rat, and such hypersensitivity reactions may involve a population of mast cells which reside in the liver.

Animals↗
PubMed1999

The effectiveness of different rat IgG subclasses as IgE-blocking antibodies in the rat basophil leukaemia cell model.

The degranulation of mast cells in an allergic response is initiated by the aggregation of high-affinity IgE receptors (Fc epsilon RI) by IgE and antigen. Recently it has been shown that such degranulation can be inhibited by cross-linking Fc epsilon RI and low-affinity IgG receptors (Fc gamma RII) which are also expressed by mast cells. The ability of various monoclonal antibodies to block the degranulation of rat basophil leukaemia (RBL) cells sensitized with IgE antidinitrophenyl (DNP) antibodies has been investigated. Sensitized cells were challenged with immune complexes formed using varying concentrations of antigen, and of both high- and low-valency antigen. It is reported here that rat IgG1 antibodies, which are associated in the rat with a Th1-type response, act as highly effective blocking antibodies over a wide concentration range. Rat IgG2a antibodies, which are associated with a Th2-type response, were able only to inhibit degranulation when immune complexes were formed with very low concentrations of high-valency antigen (DNP32-HSA). Under these conditions, some inhibitory activity was seen with high-affinity murine IgA anti-DNP but not with low-affinity rat IgG2b anti-DNP antibody-containing immune complexes. In addition to this inhibitory activity, IgG2a antibodies were shown to be capable of inducing degranulation of cells via unoccupied Fc epsilon RI. These results demonstrate that blocking activity may arise via both inhibitory receptors and by masking of antigen.

Animals↗
PubMed1998

The development of a risk-adjusted capitation payment system: the Maryland Medicaid model.

This article describes the risk-adjusted payment methodology employed by the Maryland Medicaid program to pay managed care organizations. It also presents an empirical simulation analysis using claims data from 230,000 Maryland Medicaid recipients. This simulation suggests that the new payment model will help adjust for adverse or favorable selection. The article is intended for a wide audience, including state and national policy makers concerned with the design of managed care Medicaid programs and actuaries, analysts, and researchers involved in the design and implementation of risk-adjusted capitation payment systems.

Ambulatory Care↗
PubMed1996

Humanization and molecular modeling of the anti-CD4 monoclonal antibody, OKT4A.

OKT4A, a murine mAb that recognizes an epitope on the CD4 receptor, is a potent immunosuppressive agent in vitro and in a variety of nonhuman primate models of graft rejection and autoimmune disease. Initial human cardiac transplant trials suggest that OKT4A does not cause either cytokine release syndrome or CD4+ cell depletion, but does induce a human anti-mouse Ab (HAMA) response despite strong concurrent immunosuppression. To further investigate the potential of OKT4A as an immunomodulator, it was necessary to decrease its immunogenicity. Therefore, we developed a humanized version of this Ab (gOKT4A-4), which has the same binding affinity and in vitro immunosuppressive properties of OKT4A, but retains only three murine sequence-derived amino acid residues outside of the complementarity-determining regions (CDRs). Detailed computer modeling of both OKT4A and gOKT4A-4 provided a computational rationale for the changes necessary to regain activity after humanization. This has also provided a plausible representation of the Ag binding site. Preliminary clinical results with gOKT4A-4 suggest that we have eliminated the immunogenicity observed in the parent murine Ab.

Amino Acid Sequence↗
PubMed1996

Replication of Australian porcine isolates of Ileal symbiont intracellularis in tissue culture.

Ileal symbiont intracellularis (ISI) isolated from Australian cases of PIA and PHE was replicated in the rat ileum enterocyte cell line IEC 18. The number of ISI within cells varied, as did the number of ISI infected within the monolayer. At 24 h post infection a large number of cells were infected with approximately 100 ISI per cell. At the termination of infection, fewer IEC 18 cells were infected but ISI had replicated to fill the cell cytoplasmic space. Numerous foci of infected cells were visible in the monolayer, containing as many as 15 densely infected cells. Division of ISI infected cells indicated the transmission of ISI in the cytoplasm to daughter cells. This suggests that the replication of ISI in culture appears to be reasonably cell dependent. No cytopathic effects were observed in the infected cultures.

Animals↗
PubMed1996

Rat basophil leukaemia (RBL) cells sensitized with low affinity IgE respond to high valency antigen.

BACKGROUND: The very low concentrations of IgE antibodies in serum make investigations of the affinity of allergen-specific antibodies extremely difficult. In the absence of such studies, the fact that low IgE concentrations are capable of inducing powerful effector function has encouraged the view that IgE antibodies are typically high affinity antibodies. Yet the phenomenon of allergic cross-reactivity suggests that lower affinity IgE antibodies may sometimes be of clinical significance. OBJECTIVES: To investigate the effect of antibody affinity upon mast cell sensitivity in an in vitro model. METHODS: Rat basophil leukaemia (RBL) cells were sensitized with one of three monoclonal IgE antibodies which bind to trinitrophenylated proteins with varying affinity. Serotonin release was measured after challenge of sensitized cells with trinitrophenylated human serum albumin (TNP-HSA). RESULTS: Low valency TNP3-HSA failed to stimulate degranulation of RBL cells sensitized with SPE-7 anti-DNP IgE, which binds TNP with low affinity. However, upon challenge with high concentrations (1250 ng/mL) of TNP8-HSA, or as little as 10 ng/mL of highly substituted TNP23-HSA, low levels of degranulation were seen. A similar relationship between antigen valency and cell sensitivity was seen with cells sensitized with the H-l epsilon-DNP anti-DNP IgE, which binds with moderate affinity to TNP proteins. CONCLUSION: High valency antigen is capable of activating RBL cells sensitized with low affinity antibody. This has important implications for our understanding of allergic sensitization. It also suggests that the long-recognized relationship between antigen valency and RBL cell sensitivity may partly reflect the high functional affinity of cell-bound IgE when directed against multivalent antigen.

Animals↗
PubMed1995

Antigen valency as a determinant of the responsiveness of IgE-sensitised rat basophil leukemia cells.

Rat basophil leukemia (RBL) cells were sensitised with varying proportions of monoclonal IgE anti-ovalbumin (OVA) and anti-DNP antibodies, and serotonin release was measured after challenge with aggregated OVA or dinitrophenylated human serum albumin (DNP-HSA). Highly aggregated OVA was shown to provoke the degranulation of RBL cells that had been sensitised with an IgE preparation containing 2% IgE anti-OVA antibodies. Highly substituted DNP32-HSA induced degranulation of RBL cells sensitised with just 0.5% antigen-specific IgE. When cells were sensitised with high percentages of specific IgE, maximum degranulation was seen at concentrations of 2 micrograms/ml (aggregated OVA) and 50 ng/ml (DNP-HSA), while moderate degranulation was still seen at antigen concentrations as low as 50 and 2 ng/ml, respectively. Low-molecular weight aggregates of OVA and low-valency DNP4-HSA only stimulated degranulation when high percentages of RBL Fc epsilon receptor were occupied by antigen-specific IgE. The sensitising abilities of two anti-DNP monoclonal antibodies of differing affinities were compared. When challenged with low-valency antigen, only cells sensitised with the higher-affinity monoclonal antibody exhibited moderate levels of degranulation. Degranulation required exposure to high antigen challenge doses (5 micrograms/ml). Cells sensitised with either monoclonal antibody responded strongly when challenged with a wide range of concentrations (1-250 ng/ml) of high-valency DNP32-HSA, although greater sensitivity was always seen with the higher-affinity antibody. These results suggest that antigen valency is a critical parameter for mast cell function, and that low-affinity antibody may be capable of sensitising mast cells to high-valency antigen.

Animals↗
PubMed1994

Humanization of the murine anti-human CD3 monoclonal antibody OKT3.

OKT3 is a murine monoclonal antibody which recognizes an epitope on the epsilon-subunit within the human CD3 complex. OKT3 possesses potent immunosuppressive properties in vivo and has been proven effective in the treatment of renal, heart and liver allograft rejection. Despite its efficacy, significant problems remain associated with OKT3 therapy, i.e. T-cell activation and the anti-murine antibody response. To address the problem of the anti-murine antibody response we have constructed humanized versions of OKT3. One of the humanized derivatives, gOKT3-7 incorporating the OKT3 complementarity determining regions plus a small number of alterations to the human framework, has an affinity of 1.4 x 10(9) M-1 compared with 1.2 x 10(9) M-1 for the murine OKT3. A humanized antibody (gOKT3-1) incorporating only the CDRs from OKT3 was found to be functionally inactive, confirming the requirement for nonCDR substitutions. gOKT3-7 retains the ability of mOKT3 to induce T cell proliferation in vitro and appears to be a good candidate for further development for in vivo therapy.

Amino Acid Sequence↗
PubMed1992

Effect of a single amino acid mutation on the activating and immunosuppressive properties of a "humanized" OKT3 monoclonal antibody.

The binding specificity of the murine OKT3 has been transferred into a human antibody framework to reduce its immunogenicity. This "humanized" anti-CD3 mAb (gOKT3-5) was previously shown to retain, in vitro, all the properties of native OKT3, including T cell activation, which has been correlated, in vivo, with the severe side effects observed in transplant recipients after the first administration of the mAb. T cell activation is thought to be triggered by the cross-linking mediated by the antibodies between T cells and Fc receptor-bearing cells. In this study, we introduced a single amino acid mutation from a leucine to a glutamic acid at position 235 in the Fc receptor binding segment of the gOKT3-5 mAb to produce Glu-235 mAb. This mutation generated a 100-fold decrease in the affinity of the antibody for the Fc receptor on U937 cells, without affecting Ag binding. In parallel, we observed a marked reduction in the T cell activation triggered by the mAb (proliferation, cell surface expression of early activation markers including Leu 23 and IL-2R, and release of TNF-alpha, IFN-gamma, and granulocyte macrophage-CSF). In contrast, the mutated mAb retained suppressive properties similar to the gOKT3-5 mAb, as assessed by significant modulation of the T cell receptor complex and suppression of Ag-specific CTL activity. We conclude that this anti-CD3 mAb bearing a single amino acid mutation in its Fc portion retains important immunosuppressive properties, while exhibiting significantly less T cell activation than OKT3 in vitro. This drug might achieve potent immunosuppression while minimizing acute toxicity in vivo and thus be useful in transplantation as well as in autoimmune diseases.

Amino Acid Sequence↗
PubMed1991

Bovine milk, including pasteurised milk, contains antibodies directed against allergens of clinical importance to man.

Pasteurised and raw bovine milk and bovine colostrum samples were assayed by enzyme-linked immunoassay for the presence of antibodies directed against a selection of allergens of importance in human atopic disease. Samples were tested for the presence of antibodies directed against or cross-reacting with ryegrass pollen, house dust mites, Aspergillus mould and wheat proteins. Antibodies of each specificity were detected in every sample tested, including all samples of commercial pasteurised milk. The results are discussed with reference to a hypothesis that dietary xenogeneic antibodies may play a role in the emergence of some human atopic disease, and the recent demonstration that oral immunisation with xenogeneic antibodies may lead to the production of anti-immunoglobulin antibodies including anti-idiotypic antibodies.

Allergens↗
PubMed1991

Oral immunization with xenogeneic antibodies stimulates the production of systemic and mucosal anti-idiotypic antibodies.

The humoral and mucosal immune responses to oral immunization with xenogeneic antibodies were studied using an animal model in which female rabbits were fed daily doses of the MOPC-315 murine IgA antibody, and were mated during the course of the feeding programme. Serum and colostrum samples were assayed for the presence of anti-idiotypic antibodies by ELISA assay, before and after depletion of anti-IgA antibodies, by affinity chromatography using another murine IgA idiotype. It was shown that all animals responded to exposure to the MOPC-315 idiotype with the production of serum anti-murine immunoglobulin antibodies and that four of six animals produced serum anti-idiotypic antibodies. That the immune response included antibodies directed against the antigen-binding site was confirmed by competition ELISA assay. Mucosal IgG and IgA anti-immunoglobulin antibodies were present in milk from all antibody-fed rabbits tested, and IgA anti-idiotypic antibodies were detectable in the colostrum of one rabbit. The results provide some support for the hypothesis that human exposure to xenogeneic antibodies, most commonly bovine milk immunoglobulins, may provoke the production of anti-idiotypic antibodies, and that such exposure may lead to disturbances of immune regulation.

Administration, Oral↗
PubMed1990

Biochemical and immunochemical comparison of Africanized and European honeybee venoms.

Africanized honeybees (HBs) pose a hazard to both normal and sting-sensitive subjects in certain areas of Central and South America, and it is predicted that they will soon be present in the southern United States as well. Using an electrical stimulation device, we collected Africanized HB venom (AHV) in Venezuela and European HB venom (EHV) in Louisiana. These venoms, along with commercial European HB venom (CHV), were compared by thin-layer isoelectric focusing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The Coomassie brilliant blue and silver-stained banding patterns of AHV and EHV were essentially identical to CHV. Western blots were prepared from SDS-PAGE gels and tested with pooled sera from EHV-sensitive subjects and then radiolabeled antihuman IgE. The resulting autoradiographs revealed similar banding patterns among EHV, AHV, and CHV. RAST-inhibition studies were performed with solid-phase CHV and pooled sera from EHV-sensitive subjects. The specific allergenic activities of the three HB venoms (allergy units per milligram of protein) were comparable. By RAST-inhibition assay with solid-phase, highly purified individual venom components, AHV and EHV both contained phospholipase A2, hyaluronidase, and high-molecular-weight allergens. The increased morbidity after Africanized HB stings is likely related to their more defensive behavior during which many bees react by stinging rather than to biochemical or allergenic differences between AHV and EHV.

Allergens↗
PubMed1989

Advanced family nursing with the control-congruence model.

This article describes family nursing with the control-congruence model (CC-model) developed at Wayne State University. The model is appropriate for clinical nurse specialists of all nursing disciplines who assist families to improve functioning together in order to cope with stress. Nursing care focuses on four dimensions of family functioning: system maintenance; system change; togetherness; and individuation. Two assessment tools are used: the assessment of strategies in families--functioning, which measures the emphasis on each of the four dimensions and the assessment of strategies in families--satisfaction, which assesses the satisfaction with family functioning. The paper cites four cases, one relative to each dimension, with examples of nursing care aimed at strengthening effective family strategies and introducing new behaviors. The examples include the interpretation of assessment of strategies in families scores before and after treatment.

Adaptation, Psychological↗
PubMed1989

A modernity score for individuals in Melanesian society.

Assessment of individual modernity has considerable implications for the prevention of non-communicable disease in high-risk populations experiencing rapid modernization. A scoring system for the classification of the relative modernity of individuals in Melanesian society is described. The score consisted of eight components relating to area of origin, employment, length of employment, father's employment, education, years spent in an urban centre, housing and an increment determined by the score of the spouse of the individual. The score was used in surveys of non-communicable disease in Papua New Guinea in 1985 and was validated, in one of the three communities studied, by the independent assessment of two local informants. With the use of analysis of variance and linear regression, the score was shown to be associated with obesity in both sexes. An association was also shown with age by both techniques in females. In males, age and glucose tolerance were associated with the score when using analysis of variance, but not when applying linear regression. Only three components, father's employment, education and the spouse increment proved useful when the score was used as the dependent variable in the linear regression equation. The utility of the other components may have been constrained by the narrow distribution of their scores in the populations studied.

Adult↗
PubMed1988

Xenogeneic antibodies and atopic disease.

Xenogeneic antibodies can survive food processing procedures with their biological activity intact and even enhanced. These antibodies can be absorbed from the human gut, and will function both as antigens and antibodies in the human immune system. Antibodies to bovine gamma globulins (BGG) have been detected in human sera and the family of anti-BGG antibodies must include anti-idiotypic antibodies, very low doses of which can influence the immune response. The hypothesis is that the human immune system may be primed by low-level exposure to xenogeneic antibodies specific for those human allergens which are ubiquitous in the farm environment, such as pollens, mites, and moulds, the result being a deleterious and inappropriate response on subsequent exposure to these allergens. Dairy products are the most important source of xenogeneic antibodies in the western diet, and the hypothesis may partly explain the association between cow's milk and allergies to substances other than milk proteins.

Adult↗