Biomedical subjects

H A Rongen

Publications and source records attributed to H A Rongen.

6 recordsLinked to original sources

PubMed1997

Liposomes and immunoassays.

Various aspects of the application of liposomes as a label in immunoassays are reviewed. Methods for the preparation of liposomes, from the basic film method to the more advanced dehydration-rehydration method, are discussed. Furthermore, the markers used in liposome labels, as well as the methods to conjugate liposomes to antigens or antibodies, are summarized. Liposome immunoassays are applied as homogeneous or heterogeneous assays. Homogeneous assays often rely on the lytic activity of complement on antibody-associated liposomes. Another group of homogeneous assays utilizes the inhibitory action of antibodies on the activity of conjugates of mellitin (a bee venom protein) with a hapten. Free mellitin conjugates are able to lyse liposomes effectively. Heterogeneous liposome immunoassays, performed either competitively or non-competitively, resemble more closely standard enzyme linked immunosorbent assays, with the enzyme being replaced by a liposome label. Washing steps are used to separate antigen-specifically bound liposomes from unbound liposomes. All bound liposomes are lysed with a detergent, giving an instantaneous amplification. Flow-injection liposome immunoassays and liposome immunosensors are also described as examples of other possible immunoassay formats.

Biosensing Techniques↗

PubMed1996

Application of xanthine oxidase-catalyzed luminol chemiluminescence in a mouse interleukin-5 immunoassay.

A chemiluminescent substrate reagent for use in a sandwich immunoassay for the model antigen mouse interleukin-5 (IL-5) was developed using xanthine oxidase and luminol. Various parameters involved in this chemiluminescent reaction have been studied, including the substrate hypoxanthine, luminol and the Fe(II)-EDTA complex. Addition of the Fe(II)-EDTA complex enhances the chemiluminescence signal considerably. The xanthine oxidase-catalyzed chemiluminescent immunoassay was compared to horseradish peroxidase-linked immunoassays with luminol as chemiluminescent, and tetramethyl benzidine as colorimetric substrate. The detection limit of the xanthine oxidase-luminol assay was found to be about 0.6 pg/ml IL-5, whereas the peroxidase-catalyzed immunoassays have detection limits of about 1.3 (HRP-TMB) and 2.9 pg/ml (HRP-luminol) IL-5.

Animals↗

PubMed1994

Function of adhesion molecules lymphocyte function-associated antigen-3 and intercellular adhesion molecule-1 on human epidermal Langerhans cells in antigen-specific T cell activation.

In addition to the interaction between the TCR and the MHC/Ag complex on the APC, optimal T cell activation also requires interaction between adhesion molecules on the APC and their ligands on T cells. We determined the presence of adhesion molecules on human epidermal Langerhans cells (LC) and their role in Ag-specific T cell activation. Freshly isolated LC did not display ICAM-1 (CD54), ICAM-2, LFA-1 (CD11a), and LFA-3 (CD58), as detected by double-color FACS analysis, using HLA-DR expression for LC identification. Upon culture, LC clearly expressed ICAM-1 and LFA-3, both already detectable after 1 day, reaching a plateau at day 2. ICAM-2 and LFA-1 were undetectable on cultured LC and attempts to induce this expression by different culture conditions remained unsuccessful. mAb against ICAM-1, LFA-1, LFA-3, and CD2, continuously present during culture, inhibited the T cell proliferative response to Candida albicans presented by cultured LC. Pretreatment of LC and/or T cells with mAb indicated that anti-ICAM-1 and anti-LFA-3 inhibited at the LC level, whereas anti-LFA-1 and anti-CD2 inhibited at the T cell level. The mAb-induced inhibition was dose-dependent, but a total blockade of the response was never achieved. Time-course observations revealed that ICAM-1 and LFA-3 on LC only functioned during the initiation phase of T cell activation. Our study demonstrates that both ICAM-1 and LFA-3 on LC considerably contribute to the generation of a T cell response. The high expression of these accessory molecules enable LC, at least in part, to perform their powerful Ag-presenting function.

Antigen-Presenting Cells↗

PubMed1994

Chemiluminescence and immunoassays.

The principles of chemiluminescence and the application of chemiluminescent labels and substrates in immunoassays are reviewed. Various immunoassay formats and all known classes of chemiluminescent molecules, including 1,2-dioxetanes, luminol and derivatives, acridinium esters, oxalate esters and firefly luciferins are described as well as the many sensitizers and fluorescent enhancers. Recent promising developments are discussed.

Animals↗

PubMed1992

A comparison of the inhibitory effects of immunosuppressive agents cyclosporine, tetranactin, and didemnin B on human T cell responses in vitro.

The agents cyclosporine, tetranactin (TN), and didemnin B (DB) were compared for their ability to inhibit proliferative human T cell responses in vitro, using anti-CD3, PHA, alloantigen, or tetanus toxoid as stimuli and using monocytes or Langerhans cells as antigen-presenting cells/accessory cells (APC/AC). We found that all three agents suppressed T cell activation in a dose-dependent fashion, irrespective of the stimulus of APC/AC type used. Both T cells and APC/AC were affected by the drugs. DB appeared to be the most potent suppressive drug (IC50 = 1-4 ng/ml), whereas CsA and TN exerted approximately similar potency (IC50 = 50-60 ng/ml). Remarkably however, DB was toxic at a concentration of 10 ng/ml, which is quite close to the inhibition-inducing dose. No toxicity was observed with CsA and TN at doses up to 5000 ng/ml. The agents TN and DB could interrupt ongoing T cell responses and could block responsiveness to exogenous recombinant IL-2. Expression of IL-2 receptors was slightly inhibited by all three drugs. Expression of MHC class II molecule HLA-D and of adhesion molecules LFA-1, LFA-3, and ICAM-1 was clearly reduced by DB, giving an explanation for the observed inhibition of cluster formation between T cells and APC/AC. Except for a slight reduction of LFA-3 by TN, CsA and TN did not affect the expression of any of these cell surface markers or the formation of clusters. Differences in the effects of CsA, TN, and DB on immune responses in vitro and on the phenotype of T cells and APC/AC suggest that these immunosuppressive drugs have different inhibitory mechanisms.

Cell Survival↗

PubMed1986

Differences in specificity and catalytic efficiency between allozymes of esterase-4 from Drosophila mojavensis.

A more than 10-fold difference in the specificity and catalytic efficiency for 1-naphthyl esters was measured between two allozymes of esterase-4 from Drosophila mojavensis. This difference is mainly caused by a difference in the affinity for the 1-naphthyl esters. The amino acid compositions of the allozymes are not significantly different, which means that the difference in primary structure is small. Small differences in primary structure generally do not result in such a large increase in catalytic efficiency and such a large shift in substrate specificity as was found in the present study.

Amino Acids↗