ZAP-70 expression is low in normal precursor B cells or hematogones

Zeta-associated protein (ZAP-70) expression has been associated with a less favorable prognosis in chronic lymphocytic leukemia (CLL). The role of ZAP-70 in immature B-cells is not well understood. Immature or precursor B lymphocytes (hematogones) often occur in clinical samples and coexpress CD10, CD38, and CD19 lacking surface immunoglobulin expression. The present study was carried out in an attempt to further elucidate the role of ZAP-70 in the spectrum of B-cells seen in clinical specimens.

ZAP-70 expression was evaluated on 25 patient samples that expressed greater than 2% of CD10(+)/CD38(bright)/CD19(+) coexpression during routine evaluation. In our sample set, the hematogone expression ranged from 2 to 18% of total leukocytes and occurred in a variety of conditions, including CLL, NHL, AML, MDS, Hodgkins Disease, and Multiple Myeloma. The method of ZAP-70 detection was that routinely applied to our clinical testing of CLL samples supplemented with the determination of ZAP-70 levels in the CD38(bright)/CD19(+) coexpressing cells.

In all cases ZAP-70 was not expressed on the CD5 negative, CD38/CD19 coexpressing precusor B cells. In all cases hematogones were found to not express significant levels of ZAP-70.

The presence of hematogones in clinical samples should be recognized so as to not adversely influence prognostic studies of ZAP-70 or CD38 in CLL.