Stains in Leukemia Diagnosis The MPO reaction is positive in cells of the granulocytic series and may be positive in monocytes. The basis of the stain is breakdown of hydrogen peroxide by the enzyme MPO, releasing an oxygen radical that reacts with a soluble substrate (e.g., diaminobenzidine or o-tolidine) to form a colored precipitate. MPO is located in the peroxisomes of neutrophils and monocytes and specific granules of eosinophils. Lymphoid cells and erythroid precursors are negative. SBB is a direct stain of phospholipid in granule membranes. The pattern of staining closely parallels that of MPO, but the SBB reaction is usually stronger. Monoblasts may contain sudanophilic granules. Erythroid precursors are negative. Auer rods are MPO- and SBB-positive. Nonspecific esterase reactivity is found in monocytes. The basis for the esterase cytochemical stains is enzymatic release of a side chain from a naphthol ring, with subsequent reaction of the free ring with a soluble color developer to generate a colored precipitate. The most commonly used substrates for NSE are α-naphthyl butyrate (ANB) and α-naphthyl acetate (ANA). Megakaryoblasts are negative with ANB staining. These features may be used to identify megakaryoblasts The PAS stain reacts primarily with glycogen, generating a fuchsia-colored precipitate. Lymphoblasts in ALL often have prominent coarse granular or block PAS staining, but the stain is of limited utility for leukemia diagnosis, as it is not specific for lymphoblasts.
Posted on: Mon, 28 Apr 2014 13:30:36 +0000