Immunofluorescence Procedures


Laboratory Services Section

The following assays are IFAs performed in the Molecular and Serological Analysis Group :

  • Ehrlichia antibody
  • Fluorescent Treponemal antibody (FTA)
  • Legionnella antibody
  • Mumps IgM antibody
  • Q Fever antibody
  • Rocky Mountain Spotted Fever antibody
  • Toxoplasma IgG antibody
  • Typhus antibody

Fluorescent-antibody (FA) techniques are still used today to detect antigens and antibodies, although not as widely since the advent of EIAs.  There are direct and indirect methods similar to the formats used in EIAs.  Antigens are usually detected by the direct method, and antibodies are usually detected by the indirect method (IFA).  In the Diagnostic Serology Section, only IFAs are performed.

Indirect Fluorescent Antibody Test (IFA)

  1. Microbial antigen is dried on a glass slide and treated with a chemical fixative
  2. Dilutions of patient serum are incubated with the antigen on the slide, and then rinsed
  3. A fluorescein-labeled antibody (conjugate) is added
  4. The slides are rinsed and dried, and then read under a fluorescence microscope

The slides are examined for bright areas of apple-green fluorescence and compared to positive and negative controls.  The presence of fluorescence indicates the presence of antibody to the antigen on the slide. 

Indirect Fluorescent Antibody Test steps on a glass slide


This is an example of an IFA for toxoplasma antibodies.  On the left is a well of a slide positive for toxoplasma antibodies, on the right is a well negative for antibodies to toxoplasma.



This is an example of an IFA for ehrlichia  antibodies.   Ehrlichiae are obligate, intracellular rickettsiae, which cause a disease similar to Rocky Mountain Spotted Fever.  The actual organisms are the inclusions seen within the cells to the right.



Last updated September 16, 2010