Immunology: diagnosing infections

What is diagnostic immunology?

• Term for a variety of diagnostic techniques that rely on the specificity of the bond between antibodies and antigens

• Using antibodies to identify pathogens

Uses serological tests• Direct tests detect antigens (from patient sample).• Indirect tests detect antibodies (in patient′s serum).

What are some serological tests?

• Monoclonal antibodies• Many techniques

– Precipitation reactions– Agglutination reactions– Complement-fixation reactions– ELISA– fluorescent-antibody– Western blot

What are monoclonal antibodies?• Produced by specialized B cells.

– Single type of Ab. • From any substance– Possible to create monoclonal

antibodies that specifically bind to that substance

• Can serve to – detect or purify that substance

• Useful– Uniform– Highly specific– Produced in large quantities

What are monoclonal antibodies?• Immunotoxins: Mabs conjugated

– with a toxin to target cancer cells.• Chimeric mabs: Genetically

modified mice that produce Ab – with a human constant region.

• Humanized mabs: Mabs that are mostly human– except for mouse antigen-binding.

• Fully human antibodies: Mabs produced from a human gene– on a mouse.

What are precipitation reactions?• Involve

soluble antigens with antibodies.

Figure 18.4

What are agglutination reactions?

• Involve particulate antigens and antibodies.

• Antigens may be– On a cell (direct

agglutination).– Attached to latex

spheres (indirect or passive agglutination).

Figure 18.5

What is direct agglutination?• Antibody titer• Is the concentration

of antibodies against a particular antigen.

Figure 18.6

Reactions in indirect agglutination

What are complement fixation reactions?

What is ELISA?Enzyme-linked immunosorbent assay

A positive direct ELISA to detect antigens

A positive directELSIA to detectantibodies

What is fluorescent-antibody testing?

• Tagged antibodies

Direct method

Indirect method

What is the Western Blot?

• Similar to Southern Blot

• Proteins, not DNA