Human Meprin Alfa Metalloprotease Is Differentially Expressed in Peripheral Blood Cells.

Meprin metaloproteases are highly expressed in the apical brush-border of the intestinal and renal proximal tubule epithelia. However, the expression and function of these metaloproteinease in other tissues have not been well established. Using a specific antisera raised against rat but cross-reactive with human Meprin Alfa, we examined the expression of this protein in human peripheral blood cells. Flow cytometry analysis showed that the post-, but not the pre-, immune sera stained strongly for the CD14+ monocytes and moderately for CD56+ NK cells, but not for CD3+ T and CD19+ B cells. To confirm Meprin Alfa expression at the RNA level, peripheral blood cells were fractionated based on the expression of the above surface markers, followed by detection of Meprin Alfa message RNA by semi-quantitative RT-PCR. Consistent with the flow cytometry data, Meprin Alfa messages were detected only in cell fractions containing monocytes and NK cells but not T and B cells. Subsequent sequencing of the PCR amplified fragments confirmed the specificity of the PCR amplification. Interestingly, flow cytometry analysis further revealed that while the expression of Meprin Alfa was maintained in the macrophages differentiated in vitro from isolated monocytes, its expression was reduced in monocytes-derived immature dendritic cells (DC) and diminished in mature DC. The differential expression of Meprin Alfa in the peripheral blood cells suggests important physiological function of this protein in the immune system.