AGGLUTINATION TESTS and IMMUNOASSYS
1. SerologyAGGLUTINATION TESTS and IMMUNOASSYS BASICS Dr.T.V.Rao MD
2. Methods for Ag-Ab detection• Precipitation• Agglutination• Hemagglutination and Hemagglutination inhibition• Viral neutralization test• Radio-immunoassays• ELISA• Immunofluorescence• Immmunoblotting• Immunochromatography 1/11/2013 Dr.T.V.Rao MD 2
3. Agglutination• Agglutinins – Antibodies that produce such reactions• Involves two-step process: – Sensitization or initial binding – Lattice formation or formation of large aggregates1/11/2013 Dr.T.V.Rao MD 3
4. Agglutination• Types of particles that participate in such reactions: –Erythrocytes –Bacterial cells –Inert carriers such as latex particles1/11/2013 Dr.T.V.Rao MD 4
5. Agglutination tests• Antibodies can agglutinate multivalent particulate antigens, such as Red Blood Cells (RBCs) or bacteria• Some viruses also have the ability to agglutinate with RBCs.• This behavior is called agglutination.• Serological tests based on agglutination are usually more sensitive than those based on precipitation1/11/2013 Dr.T.V.Rao MD 5
6. Examples• Slide Agglutination Test• Plate Agglutination Test• Tube Agglutination Test• Passive Agglutination Test• Microscopic Agglutination Test• Haemagglutination test (HAT)1/11/2013 Dr.T.V.Rao MD 6
7. Steps in Agglutination• Primary phenomenon (SENSITIZATION) First reaction involving Ag-Ab combination Single antigenic determinant on the surface particle 1) Initial reaction: rapid and reversible 2) Cross link formation visible aggregates (stabilization)1/11/2013 Dr.T.V.Rao MD 7
8. Secondary phenomenon:LATTICE FORMATION – Ab + multivalent Ag stable network (visible reaction) – conc. of Ag and Ab – Governed by physiochemical factors: • Ionic strength of milieu • pH • temperature1/11/2013 Dr.T.V.Rao MD 8
9. Secondary Phenomenon • Lattice Formation • The Fab portion of the Ig molecule attaches to antigens on 2 adjacent cells-visible results in agglutination • If both antigen and antibody are SOLUBLE reaction will become visible over time, ie, precipitation1/11/2013 Dr.T.V.Rao MD 9
10. DIRECT AGGLUTINATION- Test patient serum against large, cellular antigens to screen for the presence of antibodies.• Antigen is naturally present on the surface of the cells.• In this case, the Ag-Ab reaction forms an agglutination, which is directly visible.1/11/2013 Dr.T.V.Rao MD 10