- Primary serological tests: (Marker techniques) e.g. Enzyme linked immuonosorbent assay (ELISA) Immuno flurescent antibody technique (IFAT) Radio immuno assay (RIA) - Secondary serological tests: e.g. Agglutination tests Complement fixation tests (CFT) Precipitation tests Serum neutralization tests (SNT) Toxin-antitoxin test Classification of antigen-antibody interactions:

- Antigens are whole cells (eg. RBC or bacteria). - Antibodies cross-link the antigens. - Types of tests : - Rapid plasma test (syphilis). - Cold agglutinin test (mycoplasma). - Weil-Felix test (rickettsial). - Latex agglutination test (pregnancy). Agglutination :

- Agglutination reactions involve whole cell antigens, while precipitation reactions involve soluble antigens. - Cellular/molecular view of agglutination and Precipitation reactions that produce visible Ag- Ab complexes. Agglutination : ( continued )

- The rapid plasma reagin (RPR) test is available as a kit. The patient's serum is mixed with cardiolipin on a plastic-coated card that can be examined with the naked eye. Rapid plasma reagin ( RPR test )

Precipitation - Soluble antigens. - Binding of antibody to antigen, makes the complex insoluble or visible. - Types of test : - Tube precipitation. - Ouchterlony (double diffusion). - Immunoelectrophoresis.

Precipitation : ( Continued ) - Precipitation reactions

Precipitation : ( Continued ) Ouchterlony (double diffusion)

Precipitation : ( Continued ) Precipitation curve :

Complement fixation - Antibody (lysin), antigen, complement, and sensitized sheep rbc are required. - Complement is fixed to a Ab-Ag-complex. -Fixed complement cannot participate in rbc lysis positive reaction or identification.

Complement fixation test

Nephelometry ( Turbidimetry ) - Nephelometry is a technique used in immunology to determine levels of IgM, IgG, and IgA.

Immunofluorescence - A monoclonal antibody labeled with a fluorescent dye : - Direct testing. - Indirect testing.

- An example of direct and indirect immunofluorescence testing. Immunofluorescence testing

Common assays - Radioimmunoassay (RIA). - Enzyme-Linked Immunosorbent Assay (ELISA).

Radioimmunoassay (RIA) - Antibody or antigen is labeled. - Detect corresponding antibody or antigen. - Competition between unlabeled and labeled molecule.

Radioimmunoassay (RIA) : ( Continued )

Enzyme-Linked Immunosorbent Assay (ELISA) - Safer & less costly than RIAs. - ELISA methods can detect any infectious disease provided if we have antibodies and antigen to any infection, enzyme or any substance.

Enzyme-Linked Immunosorbent Assay (ELISA) - Horseradish peroxidase or alkaline phosphatase. - Enzyme releases dye (chromogen). - Types of test : - Indirect ( Non-competitive ). - Capture or Sandwich. - Competitive ELISA.

Abs Ex: detecting the presence of serum Abs against HIV An example of the indirect ELISA method

An example of the capture ELISA method

An example on competitive ELISA method