Modification of immunocytochemical ZAP-70 assay for potential clinical application in B-cell chronic lymphocytic leukemia.

The ZAP-70 protein is a member of the Syk/ZAP protein tyrosine kinase family, normally expressed in T cells and NK cells but not found in normal, mature B cells. The protein plays a critical role in the initiation of T-cell signaling. Leukemic cells from patients with B-cell chronic lymphocytic leukemia (B-CLL) that expressed nonmutated immunoglobulin V genes were found to express levels of ZAP-70 protein that were comparable to those detected in T cells of healthy adults. The ZAP-70 protein expression can be evaluated by flow cytometry and may be used as a prognostic marker in B-CLL patients. We modified the method of immunocytochemical assessment of ZAP-70 expression. The traditional two-step method with monoclonal anti-ZAP-70 antibody in the first step followed by FITC-conjugated goat anti-mouse IgG was changed for one-step method with monoclonal anti-ZAP-70 antibody labeled by Zenon Alexa Fluor 488. The method is simple and fast. The major advantage of Zenon labeling technique is its compatibility with simultaneous staining of surface antigens. The cells may be earlier immunostained for CD3, CD19 and/or CD5 to compare of the ZAP-70 kinase expression in B and T cells.