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Biomedical subjects

I Todd

Publications and source records attributed to I Todd.

83 records · Page 5Linked to original sources
PubMed1979

Interference reflection microscopy. A quantitative theory for image interpretation and its application to cell-substratum separation measurement.

We propose a quantitative theory of microscope interferometry where the specimen is illuminated by a cone of monochromatic light of solid angle 0 - 100 degree, corresponding to an illuminating numerical aperture of 0 to approximately 1.2. Computed results compare favorably with photometric measurements of fringe irradiance for a water wedge 0 - 2,000-nm thick. The interpretation of cell-substratum interference images is discussed in relation to the theory. We conclude that in assessing cell-glass separation, the cytoplasmic thickness does in general contribute significantly to the final image, but this contribution is minimized at high illuminating apertures. In these circumstances, however, normal incidence theory is inapplicable and the theory for finite illuminating aperture is essential. Neglect of this fact can lead to errors of up to 100% in estimated cell-glass separation.

DNA↗
PubMed1979

Comparison of antigen-specific I-region-associated cell interaction factors.

Two basic types of factors reacting with anti-I region (anti-Ia) antisera are compared, those derived from macrophage-like antigen presenting cells and others derived from T-lymphocytes, of either the suppressor or helper type. Despite the common property of reacting with anti-Ia antisera, the two sets of factors differ by many criteria. Macrophages, upon culture with antigen, release complexes of Ia antigen and a fragment of the original immunogen. This material is only produced by responder macrophages and thus appears to be a soluble Ir gene product. The genetic restriction of the T-macrophage interaction was investigated in chimeras, and it was found that the host environment as well as the donor genotype was of importance in determining restrictions, which were thus not really directed to "self." There was no evidence for intrinsic T-cell Ir genes, as nonresponder stem cells developed into responder T-cells in a (responder X nonresponder) F1 environment. However, these cells only responded in the presence of responder macrophages. Specific T-cell factors are different in nature. These all react with anti-Ia antisera, but the nature or function of the T-cell Ia is unknown. The basic structure involves a VARIAble region" responsible for antigen binding which, as it reacts with anti-idiotype antisera and anti-variable region framework antisera is an immunoglobulin variable region. There is also a "constant region," defined by its biological properties as well as by specific rabbit antisera. This two-region nature of specific factors is reminiscent of immunoglobulin structure and it is a reasonable hypothesis that the constant region is linked to the Ig cluster of genes.

Animals↗
PubMed1975

Adhesion of red blood cells to charged interfaces between immiscible liquids. A new method.

We have devised a method of making a flat oil/water interface which remains flat on inversion. Cell adhesion to the interface can be observed microscopically. Glutaraldehyde-fixed human red blood cells adhere to the interface between physiological saline and hexadecane containing surface-active behenic acid at pH values below about 7-5. At high pH values, cells are prevented from adhering due to dissociation of the carboxyl groups of behenic acid oriented in the interface. The negative red cells are driven away electrostatically. Adherent and non-adherent cells remain on the aqueous side of the interface and do not appreciably deform it when adherent. Cells are electrostatically attracted to a similar interface containing positively charged octadecyltrimethylammonium ions. Cells also adhere to an interface containing octadecanol, which carries no charge. Underlying both electrostatic repulsion and attraction between red cells and oil/water interfaces is an attractive force which may be of electrodynamic (van der Waals) origin.

Cell Adhesion↗
PubMedDate not supplied

Factors affecting remission and survival in patients with advanced Hodgkin's disease treated with MVPP.

One hundred and fourteen patients with clinical or pathological stages IIIB and IV Hodgkin's disease have been treated with MVPP chemotherapy followed by radiotherapy to sites of previously bulky disease. The minimum follow-up is 2 years with a median of 5 years. The overall remission rate was 92 per cent with 74 per cent achieving CR. A discriminant analysis showed that the presence of bulky disease was the only independent factor that predicted a lower chance of CR (66 per cent vs 82 per cent, P = 0.045). The 5-year survival was 70 per cent overall and 85 per cent for CR patients. A Cox multivariate analysis demonstrated that stage III disease, age less than 36 years and female sex were all variables which independently predicted a more favourable prognosis in terms of overall survival. However, a similar analysis for survival of CR patients showed that age less than 36 years and the absence of bulky disease were the only two factors to independently predict a more favourable outcome. Of 14 patients who did not receive the chemotherapy according to protocol 5 have relapsed compared to 7 of 70 who did. A Cox analysis confirmed that this variable was the only one of significant prognostic import in predicting relapse-free survival. Using the Cox analyses we have been able to devise a scoring system which accurately predicts the outcome for these patients. This model may be useful in determining which patients have a worse prognosis following treatment with MVPP thus allowing more intensive therapy to be given to such patients while minimising treatment for those with favourable features.

Adolescent↗
PubMedDate not supplied

HLA class II induction in human islet cells by interferon-gamma plus tumour necrosis factor or lymphotoxin.

HLA class II molecules are surface glycoproteins which are essential in the initiation of immune responses. It has been postulated that induction of class II in epithelial cells such as endocrine cells, which are normally class II negative, may result in autoimmunity. In type I diabetes, islet beta cells, the target of the autoimmune process, selectively express class II antigens. But in contrast to most other cell types, islet beta cells are not stimulated to express class II by interferon-gamma (IFN-gamma) and thus the conditions under which this induction occurs have been particularly elusive. The cytotoxins tumour necrosis factor (TNF) and lymphotoxin (LT) synergize with IFN-gamma in a number of activities. We report here that IFN-gamma in combination with either TNF or LT induces islet cell class II expression. This finding has important implications for the pathogenesis of type I diabetes and the understanding of the differential control of class II expression.

Antibodies, Monoclonal↗
PubMedDate not supplied

Electrical stimulation of transforming growth factor-beta 1 secretion by human dermal fibroblasts and the U937 human monocytic cell line.

The in vitro effects on human dermal fibroblasts and the U937 human monocytic cell line of three phases of electrical microcurrents generated by the ACE Stimulator were investigated. The growth and viability of growing and confluent dermal fibroblasts were not directly influenced by the separate microcurrent phases. One form of microcurrent (designated phase 1) stimulated both dermal fibroblasts and U937 cells to secrete transforming growth factor-beta 1 (TGF-beta 1), which is an important regulator of cell-mediated inflammation and tissue regeneration, but none of the three phases stimulated secretion of the pro-inflammatory cytokine interleukin-6 by U937 cells. The stimulation of TGF-beta 1 secretion in these experiments was not dramatic (a median increase over control levels of 20-30%), although it could be biologically significant.

Animal Testing Alternatives↗
PubMedDate not supplied

Pancreatic beta-cell damage. In search of novel pathogenetic factors.

A model for the possible pathogenesis of insulin-dependent diabetes mellitus (IDDM) is presented. It is partly based on studies of autoimmune thyroiditis and founded on the idea that inappropriate class II molecule expression in insulin-producing beta-cells of pancreatic islets could cause an organ-specific autoimmune disorder. The model is supported by results of several IDDM case studies as well as by the critical evaluation of the known effects of various lymphokines and lymphotoxins on endocrine target tissues. The possible roles of islet capillary endothelial cells and islet cell antibodies in the pathogenesis of IDDM are discussed.

Diabetes Mellitus, Type 1↗