Immunoenzymatic reactions (ELISA-Enzyme Linked Immunosorbent assay)

ELISA tests are used to detect either viral antigens or antiviral antibodies using an enzyme marking; this is then put in contact with its substrate, and a colour reaction that is finally read to a device called spectrophotometer (apparatus that reads color reactions) will appear.

-The serological tests used for antibody detection are now based on third-generation ELISA (most modern) techniques.  Antibodies in the patient’s plasma are detected by binding synthetic proteins fixed on a solid medium. The presence of antibodies in the patient’s serum is demonstrated by a colour reaction due to the conjugated enzyme that reacts with the substrate. The reading is made at Spectrophotometer, appreciating the optical density of the samples and in parallel of certain positive and negative witnesses. There are different ELISA tests for the detection of IgM and IgG antibodies.

-The serological tests used for antigen detection are ELISA tests that also belong to the 3rd generation Immunoenzymatic tests and have extremely high specificity and sensitivity (implying the certainty of the results). Plasma antigen is detected by binding of antibodies fastened to a solid medium and by the corresponding enzyme-labelled antibodies in conjugate; finaly, detection is demonstrated by colour reaction and reading at spectrophotometer, similar to the reaction described in antibody-detection ELISA tests.

Reference

The avidity test (the type of avidity index for IgG antibodies)

It’s based on an ELISA reaction. The determination of the IgG antibodies avidity is useful for confirming the recent infection, as it has been shown that avidity is low in the acute phase of the infection and increases over time. The test allows for the differentiation of low-avid antibodies (produced in the initial stages of infection) or of high-avid antibodies (characteristics of older infections). Low avidity suggests a recent or current infection!

Western Blot test

It is a technique commonly used to confirm ELISA-by detecting antiviral antibodies separately on different antigens of the same virus, antigens are fixed on a nitrocellulose membrane. Initially the viral proteins are separated by electrophoresis, then add the patient sample and, if there are specific antibodies, they will be linked to the viral antigens against which they were synthesized. The detection of the fixed antibodies is achieved by adding an antibody related to an enzyme, finally viewed by a color reaction.

Indirect immunefluorescence reaction

Is a quick method of diagnosis, which involves the immune reaction between an antigen and an antibody marked with a fluorochrom finally read at the optical microscope in ultraviolet light.

The reaction is frequently used to highlight antigens of respiratory viruses (influenza, parainfluenza, VRS), herpes virus antigens (HSV1, HSV2, CMV), as well as for inclusions antigens.

Reaction of Hemaglutino-inhibition

Is a reaction based on the property of influenza viruses to agglutinate human red blood cells and other species (cock, guinea pig); it is due to the presence of some growths on the virion’s surface called hemagglutinins, linking sialic acid receptors on the sedimentation surface, thus producing their agglutination; specific antibodies have the property to block the hemagglutinin of influenza viruses.

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