Development and Application of a Simple Plaque Assay for the Human Malaria Parasite Plasmodium falciparum.

Malaria is caused by an obligate intracellular protozoan parasite that replicates within and destroys erythrocytes. Asexual blood stages of the causative agent of the most virulent form of human malaria, Plasmodium falciparum, can be cultivated indefinitely in vitro in human erythrocytes, facilitating experimental analysis of parasite cell biology, biochemistry and genetics. However, efforts to improve understanding of the basic biology of this important pathogen and to develop urgently required new antimalarial drugs and vaccines, suffer from a paucity of basic research tools. This includes a simple means of quantifying the effects of drugs, antibodies and gene modifications on parasite fitness and replication rates. Here we describe the development and validation of an extremely simple, robust plaque assay that can be used to visualise parasite replication and resulting host erythrocyte destruction at the level of clonal parasite populations. We demonstrate applications of the plaque assay by using it for the phenotypic characterisation of two P. falciparum conditional mutants displaying reduced fitness in vitro.

Comparison of the Hemagglutination Inhibition Test and IgG ELISA in Categorizing Primary and Secondary Dengue Infections Based on the Plaque Reduction Neutralization Test.

Secondary dengue infection by heterotypic serotypes is associated with severe manifestations of disease, that is, dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS). The World Health Organization (WHO) has recommended criteria based on the hemagglutination inhibition (HI) test to distinguish between primary and secondary dengue infections. Since the HI test has practical limitations and disadvantages, we evaluated the accuracy of WHO HI criteria and compared it with criteria based on an IgG enzyme-linked immunosorbent assay (ELISA) using a plaque reduction neutralization test (PRNT) as the gold standard. Both WHO HI criteria and IgG ELISA criteria performed strongly (16/16) in determining primary infection. However, to determine secondary infection, the IgG ELISA criteria performed better (72/73) compared to the WHO HI criteria (23/73).

Validation of Single Radial Haemolysis assay: A reliable method to measure antibodies against influenza viruses.

The Single Radial Haemolysis (SRH) assay is a serological method widely used for measuring antibodies against influenza viruses. Despite the broad application and recommendation by licensing authorities, the SRH assay has not been standardized. The aim of this study is to demonstrate how the SRH assay satisfies validation parameters of regulatory agencies in terms of specificity, precision, repeatability, intermediate precision, linearity, accuracy and robustness. This study shows that the SRH is a rapid, simple, reliable and reproducible assay, which requires only small volumes of serum samples and can be easily standardized.

In vitro induction and measurement of hemolytic plaque forming cells in man.

Following co-cultivation with sheep red cells or ovalbumin, Hypaque-Ficoll-separated human tonsillar lymphocytes were demonstrated to generate specific hemolytic PFC with maximum numbers at day 5-7. PFC were enumerated on poly-L-lysine coupled red cell monolayers in Microtest-II-plates. Plaque formation appeared to be puromycin-sensitive, complement-dependent and showed clear specificity for the antigen present during the inductive culture. Treatment of PFC with mu-chain specific antisera and complement resulted in complete inactivation of PFC; gamma-chain antisera had no effect. The development of such a simple and sensitive assay system permits the analysis of cellular interactions required for the induction of PFC responses in man.

A hemolytic plaque assay for the detection of direct and indirect antibody-forming cells to keyhole limpet hemocyanin.

A procedure is described for the in vitro enumeration of individual lymphoid cells producing antibody against Keyhole Limpet Hemocyanin (KLH) by a modification of the hemolytic plaque technique. Optimal conditions for the coupling of KLH to sheep erythrocytes by chromic chloride are described. Plaque-forming cells are detected in a liquid monolayer slide chamber assay system. The kinetics of the in vivo primary and secondary PFC responses of both rabbit popliteal lymph node cells and mouse spleen cells are described. Both direct (IgM) and indirect (IgG) plaque-forming cells can be enumerated. The method can also be used to detect an in vitro anamnestic response in dispersed rabbit lymph node cell suspensions. The method is simple, extremely sensitive and the results correlate with those previously obtained in which newly synthesized antibody was detected in similar systems using the coprecipitation assay.

The relationship between hemolytic and immunodiffusion methods for measurement of C4 in patients with immunologic disorders.

A comparison of radial immunodiffusion and functional (hemolytic) assays for C4 revealed a highly significant correlation between the two methods in patients with a variety of immunologic disorders. Immunodiffusion technics are more convenient than hemolytic assays for most clinical laboratories. C4 assays are useful for the presumptive diagnosis of hereditary angioneurotic edema, whereas C3 is usually normal in such patients. C4 is usually more sensitive than C3 in a variety of immunologic disorders, although in some patients the opposite is true, especially in hypocomplementemic nephritis.

The electrophoretic hemolytic plaque assay -- theory.

We use the mathematical theory of plaque qrowth to determine if there is merit in performing a hemolytic plaque assay in the presence of an external electric field. In particular, we study the effects of an electric field on the transport of antibodies secreted by a single lymphocyte and on the size and shape of the plaques they produce. Our results indicate that in the presence of an applied electric field: (1) The mobility of the antibodies produced by the antibody forming cell can be determined from the plaque shape. (In the electric field the plaques are no longer circular, but cigar shaped.) (2) By changing the magnitude or direction of the applied electric field more than one plaque can be generated by a single AFC. Thus changes in mobility or the rate of antibody secretion can be assayed. (3) Plaques will reach a steady state size; for good emitters (cells that secrete antibodies at a high rate or that secrete high affinity antibodies) this steady state will be achieved rapidly. Equations are given which describe both the temporal development and steady state plaque size and shape. From the equations, computer generated plots of plaques produced by typical antibody forming cells are presented. These plots are then used to show how pictures of plaques formed in an electric field can be analyzed to determine the antibody mobility.

[Modification of the local hemolysis method for the detection of antibody producing cells producing antibody to virus antigens]. / Modifikatsiia metoda lokal'nogo gemoliza dlia obnaruzheniia kletok, sinteziruiushchikh antitela k virusnym antigenam

A modification of Jerne and Nordin's method of local hemolysis for detection of antiviral antibody-synthesizing cells is described. CrCl3 was used as the coupling agent. This method is simple enough but it requires either highly purified virus antigen or viruses propagated in a heterologous culture.

Recomendación del uso de ecuaciones de corrección de valores de potasio en presencia de interferencia por hemólisis / Recommendation on the use of correction equations for potassium levels in haemolysed samples

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Verificación e implantación en un laboratorio de urgencias de un sistema de medición de los índices séricos (hemólisis, ictericia y lipidemia) en un Dimension® EXL(TM) / Verification and implementation of a serum index measurement system (haemolysis, icterus, and lipaemia) in a Dimension® EXL(TM) in an emergency laboratory

Introducción. La hemólisis, ictericia y lipidemia son los principales interferentes que pueden producir errores analíticos en la medición de magnitudes bioquímicas. Muchos analizadores incorporan sistemas de detección de interferentes, sin embargo no suelen estar verificados. El objetivo del estudio es verificar el sistema de medición HIL del analizador Dimension® EXL(TM) y comprobar la adecuada asignación por el proveedor de los valores de alerta. Material y métodos. Se ha evaluado el efecto de la hemoglobina, bilirrubina y triglicéridos en los resultados, comparando el valor de la magnitud en la muestra sin interferente con los valores obtenidos en la misma muestra con concentraciones crecientes del mismo. Se ha seguido el procedimiento recomendado por la Comisión de Metrología y Sistemas Analíticos de la SEQC. Asimismo, se ha elaborado un algoritmo de cuándo informar la presencia de interferencias (criterios clínicos y técnicos). Resultados. Todos los resultados de los índices hemolíticos incluyeron la concentración esperada del interferente, para la ictericia hubo ligeras diferencias, mientras que para la lipidemia el analizador proporcionó resultados más bajos de los esperados. En el estudio de los índices de alerta HIL hubo diferencias entre los resultados obtenidos y la información del fabricante. Se presenta el algoritmo para informar la presencia de estas interferencias. Conclusiones. La incorporación de estos índices de alerta sin una previa verificación de los mismos puede llevar a cometer errores. Una correcta verificación de estos sistemas permitiría detectar la falta de veracidad en la medición de estos interferentes o el inadecuado establecimiento de algunos índices de alerta (AU)

Introduction. Haemolysis, icterus (bilirubin) and lipaemia (triglycerides) (HIL) are the main interferences that can lead to analytical errors in the measurement of biological substances. Many analysers incorporate interference detection systems, which nonetheless are often not verified. The main objective is to verify the HIL measurement system of the Dimension® EXL(TM) analyser, and to check the correct assignment of the alert values by the supplier. Material and methods. The effect of the haemolysis, bilirubin and triglycerides on the results has been assessed by comparing the value of the quantity in a sample without interference with the values obtained in the same sample with increasing concentrations of interfering substances. The procedure recommended by the Comisión de Metrología y Sistemas Analíticos of the SEQC has been followed. An algorithm to inform of interferences, based on clinical and technical aspects, has been developed. Results. All haemolytic index results included the expected concentration of the interfering substance. Few errors were found for icterus, while for lipaemia the analyser gave results lower than expected. In the study of the HIL alert indexes, differences were found between the results obtained and the information provided by the supplier. Finally the algorithm followed in our laboratory to inform the presence of interfering substances is presented. Conclusions. The introduction of these alert indexes without a prior verification of them can lead to potential errors. Proper verification of these systems would enable detecting the lack of trueness in the measurement of the interfering substances or the inadequate establishment of some alert indexes (AU)

Characteristics of hemolytic activity induced by skin secretions of the frog Kaloula pulchra hainana

Background: Previous works had shown that scorpion venom induced neurotransmitter elevation and an inflammatory response associated with various anatomo-pathological modifications. The most dangerous scorpions species in Algeria responsible for these effects are Androctonus australis hector (Aah) and Androctonus amoreuxi (Aam). Results: Comparison of the physiopathological effects induced by the two venoms showed differences in the kinetic of cytokine release and in lung injury. The lung edema was only observed in response to Aah venom and it was correlated with cell infiltration. In order to better understand the involved mechanism in inflammatory response, we used two antagonists, atropine (non-selective muscarinic antagonist) and propranolol (ß adrenergic antagonist), which lead to a decrease of cell infiltration but has no effect on edema forming. Conclusion: These results suggest another pathway in the development of lung injury following envenomation with Aam or Aah venom.(AU)

Hemolytic plaque inhibition: the physical chemical limits on its use as an affinity assay.

An analysis of the fundamental physical chemical limits of hemolytic plaque inhibition as a method for obtaining thermodynamic and kinetic information is presented. It is shown that inhibition curve characteristics will be sensitive functions of reaction affinities only when the antibody inhibitor and antibody red blood cell reaction mechanisms are related in certain ways. It is further shown that conditions which are most sensititive to IgG affinity changes will generally not be the best for detecting changes in IgM affinity. The apparently conflicting reports on IgM maturation are completely explicable in terms of experimental requirements imposed by physical chemical characteristics of the reaction. Experiments in which maturation is observed are found to conform to the most sensitive conditions of the assay, whereas those in which it is not observed are found to conform to relatively insensitive conditions, and would therefore be capable of registering changes only when affinity shifts are large.

A plaque assay for all cells secreting Ig of a given type or class.

A modification of the hemolytic plaque assay using protein A-coated red cells is described which makes use of the fact that the Fc portion of IgG binds to protein A. A number of murine plasmacytomas secreting different classes of Ig have been tested for plaque formation with these indicator red cells. In the presence of complement-binding antibodies specific for the corresponding class of secreted Ig, between 10 and 70% of all plated myeloma cells formed plaques. The assay shows a prozone effect in excess of antibody, suggesting that complexes of antibody and secreted Ig effect lysis of the target cells. This assay can be used to enumerate cells secreting any molecules for which complement-binding antibodies are available.

Hemolysis-in-gel test in immunity surveys and diagnosis of rubella.

The hemolysis-in-gel (HIG) technique was adapted for rubella antibody determinations. Use of sucrose gradient purified virus and its coupling with CrCl3 to chicken erythrocytes resulted in gel plates that could be stored for several weeks and were suitable for reproducible antibody determinations. In a serological survey of young healthy adults the HIG values (range less than 2--13 mm) were in close correlation to those obtained by the HI test (less than 10 5o 320). The Hig test seems well suited for screening the need of vaccination. Seronegative sera (HIG less than 2,HI less than 10) gave without heat inactivation hemolysis zones ranging from 4 to 6.5 mm. Although the present rubella HIG test did not measure IgM antibodies, the test, by virtue of its accuracy and sensitivity--extending to antibody levels corresponding to HI titers 2--10--provides a simpler and more rapid means for diagnosis of rubella infections than the conventional HI and CF tests.