Expression of the membrane protein tyrosine phosphatase CD148 in human tissues

CD148, a receptor-like protein tyrosine phosphatase also known as HPTP-eta/ DEP-1, is involved in signal transduction in leucocytes and is thought to c ontribute to mechanisms of cellular differentiation. We have investigated t he in situ expression of CD148 in various fresh-frozen tissues by immunohis tology and analyzed its expression on subpopulations of activated periphera l blood leucocytes by flow cytometry. In lymphoid organs, CD148 was found t o be widely expressed on B and T cells, granulocytes, macrophages, certain dendritic cells as well as mature thymocytes. The cellular level of CD148 w as increased after in vitro activation of peripheral brood leucocytes. Comp arative analysis of tissue samples from normal gut and from patients with a ctive Crohn's disease showed that leucocytes expressing CD148 are significa ntly upregulated in inflamed tissues and that a subset of these cells co-ex press the activation marker CD25. In non-lymphoid tissues, CD148 was found to be present on many epithelial cell types with glandular and/or endocrine differentiation as well as on fibrocytes, melanocytes and Schwann cells. C D148 expression was maintained also in malignant counterparts of such tissu es. However, a marked loss of CD148 immunoreactivity was apparent in some o f the investigated high-grade carcinomas. In summary, our results confirm a role of CD148 as a leucocyte activation marker. Among non-hematopoietic ce lls, CD148 is expressed by characteristic types of epithelial and nonepithe lial cells. Downregulation of CD148 might promote dedifferentiation and aut onomous growth of such cells in malignant tumors.