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Reducing with borohydride after glut fixation reduces the double-bonds that form between glutaraldehyde and amine groups in the tissue.  As Martin just posted, this treatment reduces tissue autofluorescence  (but often does not eliminate it completely) .

In addition, reducing those bonds changes antigenticity--usually for the better.  Many immunogens are injected in their reduced form, so you aim to recreate that shape i the tissue by reducing it too.  Some "background" antigenicity may be due to double bond-containing epitopes, so you want to eliminate those.  Thirdly, permeability/penetration of the tissue is somewhat improved because the reduced bonds can rotate.

Michael


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> Hello;
> 	Please indulge a cell biologist trying to understand chemistry...
> 	We are discussing the differences between glutaraldehyde and formaldehyde fixation for immunofluorescence. When fixing with glutaraldehyde (0.1% glut with 3% PFA), we follow the fixation with sodium borohydride reduction. I understand that this converts the unused aldehyde groups to unreactive hydroxyls. Why is this step not required for formaldehyde fixation? Merely because PFA has one aldehyde group and Glut has two on the ends exposed after polymerization?
> 	Thanks.
> 	Kathy
> 
> 
> Kathryn R. Spencer, PhD
> The Scripps Research Institute
> 10550 N. Torrey Pines Road, DNC 210
> La Jolla, CA 92037