Differential surface expression of CD18 and CD44 by neutrophils in bone marrow and spleen contributed to the neutrophilia in thalidomide-treated female B6C3F1 mice.

Previously, we have reported that thalidomide (Thd) can enhance neutrophil function in female B6C3F1 mice. The present study was intended to evaluate the mechanisms underlying the enhanced neutrophil responses following Thd treatment intraperitoneally (100 mg/kg) for 14 or 28 days. Treatment with Thd increased the numbers of neutrophils in the spleen, peripheral blood, bone marrow, peritoneal cavity and lungs of female B6C3F1 mice when compared to the vehicle control mice. Thd treatment for 14 days increased the percentage and the number of neutrophils in the spleen in the first 8 h (peaking at 2 h) after the last Thd treatment, and it returned to the baseline after 24 h. However, Thd treatment for 28 days increased the percentage and number of neutrophils in the spleen even at the 24-h time point after the last Thd treatment. These neutrophils were demonstrated to be functional by the myeloperoxidase activity assay. Further studies have ruled out the possibility of an increased bone marrow granulopoiesis following Thd treatment. Flow cytometric analysis of the surface expression of adhesion molecules suggested that Thd treatment for either 14 or 28 days decreased the surface expression of either CD18 or CD44 by bone marrow neutrophils. On the other hand, the surface expression of both CD18 and CD44 by splenic neutrophils was increased following Thd treatment for 28 days but not for 14 days. No effect was produced for other cell surface molecules such as CD62L and CD11a. It was possible that decreased surface expressions of CD18 and CD44 facilitated neutrophils' release from the bone marrow; increased surface expressions of CD44 and CD18 by splenic neutrophils after 28 days of Thd treatment increased their ability to remain in the periphery. Taken together, Thd treatment increased neutrophils in female B6C3F1 mice, at least partially, through differentially modulating the surface expression of CD18 and CD44 by the neutrophils in the bone marrow and spleen.