Differential expression of somatostatin receptor subtypes in human peripheral blood mononuclear cell subsets

BACKGROUND: Somatostatin (SS)-binding sites have been demonstrated in human lymphoid tissues and peripheral blood cells. However, not much is known with respect to the SS receptor subtype (sst) expression pattern and the expression of SS itself in the immune system. OBJECTIVE: The aim of this study was to evaluate the mRNA expression of the five known sst (sst(1-5)) in peripheral blood mononuclear cell (sub)populations. Moreover, the expression of the mRNAs encoding SS and the SS-like peptide cortistatin (CST) in immune cell subsets was studied. METHODS: RT-PCR and quantitative PCR were performed to evaluate sst, SS and CST mRNA expression in cells in the basal or activated state. Fluorescence-activated cell sorter (FACS) analysis using fluorescent SS was performed to visualize sst protein on cell membranes. RESULTS: B- and T-lymphocytes selectively expressed sst(3) mRNA. sst(3) expression in B-lymphocytes was significantly lower compared with T-lymphocytes. Unstimulated, freshly isolated monocytes did not express any sst mRNA. Upon activation, monocytes selectively expressed sst(2) mRNA, whereas T-lymphocyte activation upregulated sst(3) expression. sst(2) mRNA expression on monocytes was confirmed by FACS analysis. B- and T-lymphocytes did not express SS mRNA, while both cell types expressed CST mRNA. CST mRNA expression was downregulated following T-lymphocyte activation. CONCLUSION: We demonstrate for the first time unequivocally that human peripheral blood B- and T-lymphocytes selectively express sst(3), whereas monocytes do not express sst. However, upon activation, monocytes are induced to express sst(2A). No expression of SS mRNA was detected in any cell type, whereas all cell types expressed CST mRNA. The differential expression of sst and CST mRNA in lymphocytes and monocytes s

Somastatin receptors in the hematopoietic system

Multiple interactions exist between the immune, hematopoietic, endocrine and nervous systems [1,2]. The bi-directional communication between the immune/hematopoietic and nervous systems is mediated by complex mechanisms involving multiple soluble factors (e.g., neuropeptides, neurotrophic factors, neurotransmitters and cytokines) produced by each system [3-5]. Examples of such factors are the neurotransmitter neuropeptide Y [6], produced by megakaryocytes [7], substance P (SP), which enhances the proliferation of primitive bone marrow cells and progenitors [4] and nerve growth factor (NGF), which contributes to differentiation of human basophils [8] and stimulates the release of inflammatory mediators from these cells [9]. A number of studies have demonstrated the expression of somatostatin receptors on cells derived from several hematological malignancies and have shown that somatostatin inhibits proliferation of these cells [1 0]. However, little is known of the effects of somatostatin on normal blood cell formation (hematopoiesis). This thesis comprises studies dealing with the role of somatostatin, a neuropeptide with multiple functions in the body, in hematopoiesi