Immunodiffusion is one of the methods used to diagnose fungal diseases.  Complement fixation is also used to test for some of the fungal diseases.

The specific type of immunodiffusion is called Double (Ouchterlony) microimmunodiffusion.  The procedure involves adding antigen and antibody to wells in an agarose gel.  The antigen and antibody radially diffuse from the wells. Precipitin lines form where antigen meets specific antibody.

Double (Ouchterlony) Microimmunodiffusion

1. An agarose gel is prepared with wells cut into the gel, or a template is applied to the surface of the gel.
2. Antigen is applied to the center well, control antisera and patient sera are added to the outside wells.
3. The gel is incubated and then viewed directly for precipitin lines.

The image below is of an immunodiffusion test for Coccidiomycosis (left)  and Histoplasmosis (right).  Well 3 on the left represents a patient positive for coccidiomycosis (presence of an F band).  Wells 2 and 3 on the right represent patients positive for histoplasmosis.  Well 2 contains both H and M bands, well 3 only has an M band.  For histoplasmosis, the H band is usually only present in clinically active cases, the M band occurs in acute and chronic cases, or in individuals after skin testing with histoplasmin.

The immunodiffusion procedure is used to identify Blastomycosis, Coccidiomycosis, Histoplasmosis, and Aspergillosis.