A Higher Level of Expression of the Nucleolar Protein SURF6 in Human Normal Activated Lymphocytes and in Lymphocytes of Patients with Lymphoproliferative Disorders.

Proliferation of mammalian cells is often accompanied by an increase in the content of the nucleolar proteins, which allows researchers to consider such proteins as potential activation markers. To test this assumption experimentally, we examined the expression pattern of the nucleolar rRNA processing factor SURF6 in normal (resting) peripheral blood lymphocytes, lymphocytes activated for proliferation in vitro, and in blood samples from patients with lymphoproliferative diseases. Using two methods (immunofluorescence and immunoblotting), we for the first time showed that the SURF6 protein is not detected in normal lymphocytes but can easily be visualized in lymphocytes after PHA activation and in lymphocytes of lymphocytic leukemia patients. The level of SURF6 expression in patients correlated with the aggressiveness of the disease development determined by the content of Ki-67-positive lymphocytes. These results allow the SURF6 nucleolar protein to be considered as a putative activation marker of lymphocytes in human blood disorders.