ELISA liposomes

Liposome conjugates may be used in various immunoassay procedures. The lipid vesicle can provide a multivalent surface to accommodate numerous antigen-antibody interactions and thus increase the sensitivity of an assay. At the same time, it can function as a vessel to carry encapsulated detection components needed for the assay system. This type of enzyme-linked immunosorbent assay (ELISA) is called a liposome immunosorbent assay or LISA. One method of using liposomes in an immunoassay is to modify the surface so that it can interact to form biotin-avidin or biotin-streptavidin complexes. The avidin-biotin interaction can be used to increase detectability or sensitivity in immunoassay tests (Chapter 23) (Savage et al., 1992). 

Figure 3 Cytokine secretion in immunopotentiating reconstituted influenza viro-somes (IRIV)-stimulated peripheral blood mononuclear cells (PBMC). PBMC from a healthy donor were cultured in the absence of stimuli (Neg) or in the presence of IRIV (V, 1 50 diluted) or control liposomes (L, 1 50 diluted). On days 1, 2, and 4 supernatants were harvested and the concentrations of interferon-y (A), GM-CSF (B), TNF-a (C), and interleukin-4 (D) were determined by ELISA. Abbreviations GM-CSF, granulocyte monocyte colony stimulating factor TNF-a, tumor necrosis factor-a. Source From Ref. 6.

We do not describe in details the immunological methods (immunization, Gr release assay, ELISPOT, ELISA and flow cytometry) used for the analysis of the immune responses induced by the liposome vaccines (Subheading 3.2). For comprehensive information, we refer to our publications (21-23) and to the related literature. 

Cells and liposomes ScFv concentration by ELISA, pg/mL antibody concentration... 

Antibody modification. Depending on the particular type and source of an antibody, its modification according to any of the described protocols might cause some activity decrease or even complete antibody inactivation. To escape this, immunological activity of modified and/or liposome-incorporated antibodies must be checked in a simple ELISA assay after each modification step and upon storage. If a chosen method results in antibody inactivation, and alternative protocol must be used. 

Application of assay format is attractive because it allows a mass-screening of the samples for rapid and inexpensive monitoring of the important classes of herbicides. Three assay systems based on specific properties of D1 protein have been tested, such as ELISA-type assay, DELFIA fluoro-mettic assay and assay based on the liposomes incorporated D1 protein. 

Presented experimental results suggest that application of herbicide-binding protein in sensor technology has a high potential. Several detection systems were tested in combination with D1 protein electrochemical (amperometry and cyclic voltammetry), optical (surface plasmon resonance and ellipsometty) and assays (ELISA and D1 protein- containing liposomes and DELFIA fluori-metric assay). The main mechanisms of D1 action are either on the ability of herbicides to replace the plastoquinone molecule in D1 protein and in this way change the electrochemical and optical... 

The use of liposomes instead of the more common enzyme-produced signal as seen in enzyme-linked immunosorbent assay (ELISA) has a number of advantages. 

The signal enhancement produced by liposomal biolabels is instantaneous, eliminating the timed enzymatic incubation step required in ELISA. 

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