On Thu, 22 Jul 1999, Donovan, Mark wrote:

> I am posting this for a colleague who is labeling Mast cells using IBC. She
> has two questions. 1). Does anyone know if mast cells posses any endogenous
> biotin (a little or a lot?).

  Mast cells bind avidin nonspecifically because of ionic attraction
  between avidin (a basic protein) and heparin (acid polysaccharide
  in MC granules). This results in false positive staining by ABC.
  The cure is to use the ABC reagent at pH 9.4. For more information
  see Bussolati, G & Gugliotta, P 1983. Nonspecific staining of mast
  cells by avidin-biotin-peroxidase complexes (ABC). J. Histochem.
  Cytochem. 31: 1419-1421.

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1