Somatostatin increases mitogen-induced IL-2 secretion and proliferation of human Jurkat T cells via sst3 receptor isotype

Synthesis, in vitro biological activity and docking of new analogs of BIM-23052 containing unnatural amino acids

Somatostatin (SST) is an endogenous cyclic tetradecapeptide hormone that exerts multiple biological activities via a family of five receptors. BIM-23052 (DC-23-99) D-Phe-Phe-Phe-D-Trp-Lys-Thr-Phe-Thr-NH2 is a linear SST analog with established in vitro GH-inhibitory activity and high affinity to sstr5, sstr3 and sstr2. The different SSTR subtypes are expressed in different tissues and in some tumor cells. Based on this finding, a series of new analogs of BIM-23052 with expected antitumor activity have been synthesized. The Thr at position 6 in BIM-23052 was replaced by the conformationally hindered Tle, Aib, Ac5c and Ac6c of the new analogs. The peptides were synthesized by standard solid-phase peptide chemistry methods, Fmoc strategy. The cytotoxic effects of the compounds were tested in vitro against a panel of tumor cell lines: HT-29, MDA-MB-23, Hep-G2, HeLa and the normal human diploid cell line Lep-3. All five somatostatin receptor subtypes were modeled and docking was performed to determine the binding affinity of the analogs. The new peptides exhibited different concentration-dependent antiproliferative effect on the tumor cell lines after 24 h of treatment. The compound 3B (Aib⁶) demonstrated the most pronounced antiproliferative effects on HepG-2 cells with the IC₅₀ = 0.01349 nM. Docking confirmed that all compounds bind well to SST receptors with preference to sstr3 and sstr5, which is most probably the reason for the observed biological effects.

Differentiation of human T cells alters their repertoire of G protein alpha-subunits

Because T cell differentiation leads to an expanded repertoire of chemokine receptors, a subgroup of G protein-coupled receptors, we hypothesized that the repertoire of G proteins might be altered in parallel. We analyzed the abundance of mRNA and/or protein of six G protein α-subunits in human CD4(+) and CD8(+) T cell subsets from blood. Although most G protein α-subunits were similarly expressed in all subsets, the abundance of Gα(o), a protein not previously described in hematopoietic cells, was much higher in memory versus naive cells. Consistent with these data, activation of naive CD4(+) T cells in vitro significantly increased the abundance of Gα(o) in cells stimulated under nonpolarizing or T(H)17 (but not T(H)1 or T(H)2)-polarizing conditions. In functional studies, the use of a chimeric G protein α-subunit, Gα(qo5), demonstrated that chemokine receptors could couple to Gα(o)-containing G proteins. We also found that Gα(i1), another α-subunit not described previously in leukocytes, was expressed in naive T cells but virtually absent from memory subsets. Corresponding to their patterns of expression, siRNA-mediated knockdown of Gα(o) in memory (but not naive) and Gα(i1) in naive (but not memory) CD4(+) T cells inhibited chemokine-dependent migration. Moreover, although even in Gα(o)- and Gα(i1)-expressing cells mRNAs of these α-subunits were much less abundant than Gα(i2) or Gα(i3), knockdown of any of these subunits impaired chemokine receptor-mediated migration similarly. Together, our data reveal a change in the repertoire of Gα(i/o) subunits during T cell differentiation and suggest functional equivalence among Gα(i/o) subunits irrespective of their relative abundance.

The role of cortistatin in the human immune system

Cortistatin (CST) is a recently described neuropeptide that shares high homology with somatostatin (somatotropin release-inhibiting factor, SRIF) and binds with high affinity to all somatostatin (sst) receptor subtypes. CST is currently known to have a widespread distribution in many human organs including the immune system. The activities specific to CST may be partially attributable to its binding to the growth hormone secretagogue (GHS)-receptor (GHS-R) and the orphan G-protein-coupled receptor MrgX2. Human immune cells produce CST, whereas macrophage lineage and activated endothelium express sst2, and human lymphocytes express sst3. The human thymus expresses sst1, 2, 3, MrgX2 and almost all immune cells express GHS-R. Moreover, at this very moment promising research with CST in experimental animal models is being performed. On the basis of these promising results, studies aiming to further evaluate the possibilities of CST as a therapeutic agent in human immune-mediated inflammatory diseases are warranted.

Initial Staging of Lymphoma With Octreotide and Other Receptor Imaging Agents

Somatostatin receptor scintigraphy is useful in diagnosing tumors with increased expression of somatostatin receptors. The correct use of this technique reveals the localization of neuroendocrine primary tumors and unknown metastases in approximately 90% of patients. However, somatostatin receptor scintigraphy also can image many other human tumors expressing somatostatin receptors, including malignant lymphomas and thymomas. The sensitivity of somatostatin receptor scintigraphy to image somatostatin receptor-positive tumors is very high, but due to the variable expression of specific receptor subtypes, the specificity can be relatively low. This drawback is crucial in evaluating lymphoproliferative diseases, or, in general, when immune cells are involved. The sensitivity of somatostatin receptor scintigraphy for Hodgkin's lymphoma is 95%-100%, whereas for non-Hodgkin's lymphoma it is around 80%. It has been shown that the uptake of [(111)In-DTPA(0)]octreotide in lymphomas is lower compared to the uptake in neuroendocrine tumors. This is mainly attributed to the low number of receptors on immune cells compared to neuroendocrine cells; however, ligand-induced internalization and differential receptor regulation may also participate in determining this phenomenon. Therefore, caution should be taken when interpreting data from some studies. Several new ligands are currently under study to improve these limits and the expression of other neuropeptide receptors is being investigated to provide a molecular basis for in vivo multireceptor targeting of tumors. With the use of currently available somatostatin analogs, somatostatin receptor scintigraphy does not seem to have a significant impact in patients with lymphomas for diagnostic purposes. There are a few exceptions, however. Among these, the staging and restaging of extragastric lymphoma MALT-type may present some advantages. Conversely, somatostatin receptor scintigraphy in the imaging of thymic malignancies could enhance both our diagnostic and therapeutic capabilities. Somatostatin receptor scintigraphy is diagnostically relevant in differentiating malignant from benign lesions, especially in those patients with associated paraneoplastic syndromes, and is the main criterion to select patients suitable for therapy with somatostatin analogs. Recent findings emerging from in vitro studies on somatostatin receptor physiology in immune cells will certainly reopen and expand the potential applications of somatostatin analogs for in vivo diagnostic and therapeutic options.

Evidence that L1AD3, an apoptosis-inducing cyclic peptide, binds a leukemic T-cell membrane protein receptor

Human leukemic T-lymphocytes undergo extensive and rapid apoptosis in the presence of L1AD3, a small cyclic peptide derivative of cobra cardiotoxin. The first step in this process involves its binding to membranes of susceptible cells. By the use of a biotin "handle" synthetically incorporated at the N-terminus of L1AD3, we show that binding is saturable and selective: normal human peripheral blood lymphocytes do not bind this peptide. Fluorescence resonance energy transfer experiments indicate that the binding sites are separated by at least 55 A. Loss of binding occurs if membrane proteins are enzymatically degraded, suggesting that L1AD3's target is a cell-membrane surface protein receptor. Finally, crosslinking of cyclic BTNL1AD3 peptide to a leukemic T-cell membrane surface receptor, as examined using a biotin-avidin blot, indicated a molecular weight of approximately 34,400.

Somatostatin receptor distribution and function in immune system

Somatostatin and cortistatin, a recently discovered endogenous neuropeptide relative of somatostatin, have multiple modulatory effects on the immune system. The specific somatostatin receptor distribution might in part explain the heterogeneity of effects of somatostatin or its analogs on immunocytes. In fact, somatostatin receptor subtypes are differentially expressed on specific cell subsets within the organs of the immune system and the expression is dynamically regulated and seems to depend on the traffic of these cells through and within lymphoid structure and homing in tissues. Somatostatin effects on immune cells are mainly based on autocrine and paracrine modes of action. In fact, activated cells producing somatostatin (or cortistatin) may interact with other cells expressing the receptors. Here, we review the postulated modes of action of somatostatin and somatostatin-like peptides, including the currently available synthetic somatostatin analogs, in cells of the immune system. We also discuss the wide distribution of somatostatin and its specific five receptor subtypes in immune cell lines, as well as throughout animal and human lymphoid organs, in both normal and pathological conditions.

Signal transduction of somatostatin in human B lymphoblasts

Somatostatin (SST) and somatostatin receptors (SSTR) are widely distributed in lymphoid tissues. Here, we report on the stimulatory effects of SST in Epstein-Barr virus-immortalized B lymphoblasts. By RT-PCR, we demonstrated the exclusive expression of the somatostatin receptor isoform 2A (SSTR2A) in B lymphoblasts. Addition of SST rapidly increased the cytosolic free calcium concentration [Ca(2+)](i) maximally by about 200 nM, with an EC(50) of 1.3 nM, and stimulated the formation of inositol phosphates. Furthermore, SST increased binding of guanosine 5'-O-(3-thiotriphosphate) by 50% above basal. These effects were partly inhibited by pertussis toxin (PTX), which indicates the involvement of PTX-sensitive G proteins. We provide further evidence that Galpha(16,) a PTX-insensitive G protein confined to lymphohematopoietic cells, is involved in the otherwise unusual coupling of SSTR2A to phospholipase C activation. In addition, SST activated extracellular regulated kinases and induced a 3.5-fold stimulation of DNA synthesis and a 4.4-fold stimulation of B lymphoblast proliferation, which was accompanied by an enhanced immunoglobulin formation. Thus SST exerts a growth factor-like activity on human B lymphoblasts.

Somatostatin analogs and radiopeptides in cancer therapy

Since the discovery of somatostatin (sst) in 1973, numerous chemical and biological studies have been carried out to develop sst analogs with enhanced resistance to proteases and prolonged activity. Three highly potent sst analogs-octreotide, lanreotide, and vapreotide-are now available in the clinic, and demonstrate efficacy in the treatment of tumors of the pituitary and the gastroenteropancreatic tract. The most striking effect is the control of hormone hypersecretion associated with these tumors. Available data on growth suppression in patients indicate a limited antiproliferative action, tumor shrinkage is observed in 10-20% patients, and tumor stabilization in about half of the patients for duration of 8-16 months. Eventually, however, all patients escape from sst analog therapy with regard to both hormone hypersecretion and tumor growth, the only exception being observed in acromegalic patients who do not experience tachyphylaxis even after more than 10 years of daily octreotide injection. The mechanism underlying the escape phenomenon is not yet clarified. Regarding the molecular mechanisms involved in sst antineoplastic activity, both indirect and direct effects via specific somatostatin receptors (SSTRs) expressed in the target cells have be described. Direct action may result from blockade of mitogenic growth signal or induction of apoptosis following interaction with SSTRs. Indirect effects may be the result of reduced or inhibited secretion of growth-promoting hormones and growth factors that stimulate the growth of various types of cancer; also, inhibition of angiogenesis or influence on the immune system are important factors. Five SSTR subtypes have been identified so far, which are variably expressed in a variety of tumors such as gastroenteropancreatic (GEP) tumors, pituitary tumors, and carcinoid tumors. Although all five SSTR subtypes are linked to adenylate cyclase, they are now known to affect multiple other cellular signaling systems and hence they differentially participate in the regulation of the various cellular processes. The finding of several laboratories that SSTR-expressing tumors frequently contain two or more SSTR subtypes, and the recent discovery that SSTR subtypes might form homo/heterodimers to create a novel receptor with different functional characteristics, expand the array of selective SSTR activation pathways and subsequent intracellular signaling cascades. This may lead to improved clinical protocols that take into account possible synergistic interactions between the SSTR subtypes present on the same cancer cell. Radiolabeled sst analogs, such as [(111)In]-[diethylenetriamine pentaacetic acid (DTPA)-D-Phe(1)]-octreotide (OcreoScan), have proved to be very useful for tumor scintigraphy and internal radiotherapy of SSTR overexpressing tumors. The recent introduction of the metal chelator DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) considerably improved the stability of the radioconjugates, making possible the incorporation of a variety of radionuclides, such as (90)Y for receptor-mediated radionuclide therapy or (68)Ga for positron emission tomography (PET). Another promising area is the development of sst conjugates incorporating cytotoxic anticancer drugs.

Neuroendocrine aspects of immunolymphoproliferative diseases

Exchange of information occurs between cells of neuroendocrine and immune systems. Neuroendocrine hormones may modulate lymphoid cell activities, including proliferation and mitogenesis, and immune cells may produce neuropeptides as well. Neuropetide Y is synthesized in B-cell leukaemia lymphoblasts, while substance P immunoreactivity has been detected in neoplastic haematological samples of different types of leukaemias. The presence of receptors for neuropeptides on different animal and human lymphoid cell lines, as well as in several types of animal and human lymphoproliferative diseases has been demonstrated. Species variability in receptor distribution has been shown as well. Receptor expression in immune cells may be regulated by changes in microenvironmental conditions, it may also be related to the activation and/ or proliferation state of cells. Vasoactive intestinal peptides receptors have been detected in myeloma cells, while somatostatin receptors have been first detected in vitro on resting lymphocytes and cells of the monocyte/macrophage lineage, and later on human activated lymphocytes and on lymphoblastic leukaemia cells. Somatostatin receptors have been found in biopsies from patients with malignant lymphomas. Tumor localization in non-Hodgkin lymphomas and Hodgkin's disease can be visualized by in vivo somatostatin receptor scintigraphy, contributing to establish the diagnosis and the stage of the disease. Recently. somatostatin receptors have been in vivo and in vitro detected in human thymic tumors. Although treatment of lymphoproliferative diseases with somatostatin analogs is a little explored field, partial remission was found in patients with low-grade non-Hodgkin lymphoma and cutaneous T-cell lymphoma, and a successful treatment with octreotide has been reported in patients with thymoma. Specific somatostatin receptors present in progenitors of immune cells are not expressed in the mature phenotype, while they can be detected in transformed cell lines. The possibility that this phenomenon is caused by oncogene expression cannot be ruled out. Moreover, preliminary data showed a developmental expression of somatostatin receptors in lymphoid cells, suggesting a potential role for neuropeptide receptors as differentiation markers. Although controlled studies are warranted to investigate the efficacy of the currently available analogs, somatostatinergic compounds may be of interest in the treatment of lymphoproliferative malignancies. A promising approach in refractory patients with somatostatin receptor positive malignant lymphomas may be radionuclide-targeted and cytotoxic analog therapy. These concepts increase the possibility of a wider antitumor treatment with ligands for neuroepeptide receptors than in established 'classic' neuroendocrine tumors.

The biology and physiology of somatostatin receptors

The biology and therapeutic application of somatostatin and its receptors are reviewed. The focus is on recent literature and patents, especially with regard to the specific function of each somatostatin receptor subtype. Detailed mechanisms mediating the effects of somatostatin and its analogues remain to be elucidated. Nevertheless, progress is being made towards a clear picture of the cellular signalling and physiological changes regulated by somatostatin and its receptors.

Identification of potent non-peptide somatostatin antagonists with sst(3) selectivity

Using a solution-phase parallel synthesis strategy, a series of non-peptide somatostatin analogues were prepared, and their binding affinities to the five human somatostatin receptor subtypes (sst(1-5)) were determined. Imidazolyl derivatives 2 were found to bind with moderate affinity but with high selectivity to the sst(3) receptor subtype. Further modifications of these structures led to a more potent class of ligands, the tetrahydro-beta-carboline derivatives 4. Among these, compounds 4k (BN81644) and 4n (BN81674) bind selectively and with high affinity to the sst(3) receptor subtype (K(i) = 0.64 and 0.92 nM, respectively). Furthermore, 4k and 4n reverse the inhibition of cyclic AMP accumulation induced by 1 nM somatostatin via sst(3) receptors, with IC(50) = 2.7 and 0.84 nM, respectively. The most potent compound 4n was shown to be a competitive antagonist of human sst(3) receptors by increasing the EC(50) of SRIF-14-mediated inhibition of cAMP accumulation with a K(B) of 2.8 nM (where K(B) is the concentration of antagonist that shifts the agonist dose-response 2-fold). These new derivatives are, to our knowledge, the first potent and highly selective non-peptide human sst(3) antagonists known and, as such, are useful tools for investigating the physiological role of sst(3) receptors.

Somatostatin receptor (SSTR) expression and function in normal and leukaemic T-cells. Evidence for selective effects on adhesion to extracellular matrix components via SSTR2 and/or 3

We have examined normal T-cells and T-cell lines with respect to expression of various somatostatin receptor subtypes (SSTR1--5) using RT-PCR and PCR. To evaluate the function of these receptors we have further studied the effects of subtype specific signalling on T-cell adhesion using somatostatin analogs specific for various receptors as probes. Human T-lymphocytes showed SSTR expression related to activation and stage of differentiation. Normal T-cells (peripheral blood, T-cell clone) and T-leukaemia cell lines expressed SSTR2, SSTR3 and SSTR4. Normal T-cells expressed SSTR1 and SSTR5 while T-leukaemia lines did not. SSTR5 was selectively expressed in activated normal T-cells. T-lymphocytes produced no somatostatin themselves. Somatostatin and somatostatin analogs specific for SSTR2 and/or SSTR3 enhanced adhesion of T-cells to fibronectin (FN), and to a certain extent, also to collagen type IV (CIV) and laminin (LAM). T-lymphocytes express multiple SSTR and somatostatin may therefore regulate lymphocyte functions via distinct receptor subtypes as shown here for adhesion to extracellular matrix components (ECM) via SSTR2 and SSTR3. SSTR expression also distinguishes normal and leukaemic T-cells. Our findings suggest that SSTR subtypes may be useful targets for therapy during inflammatory diseases and malignancies affecting lymphocytes.

SST3-selective potent peptidic somatostatin receptor antagonists

A family of octapeptide derivatives of somatostatin cyclized via a disulfide bridge (des-AA(1,2,4,5,12,13)[d-2Nal(8)]-somatostatin-14, ODN-8) was identified that has high affinity and selectivity for the human sst(3) somatostatin receptor subtype transfected in CCL39 cells. The binding affinity of carbamoyl-des-AA(1,2,4,5,12, 13)[d-Cys(3),Tyr(7),d-Agl(8)(Me,2-naphthoyl)]-somatostatin-14 (sst(3)-ODN-8) is equal to that of somatostatin-28 for sst(3) and less than one-thousandth that for the other four somatostatin receptor subtypes. Compound sst(3)-ODN-8 potently reverses the somatostatin-28-induced inhibition of forskolin-stimulated cAMP production (pK(B) = 9.07) and reverses the somatostatin-28-induced stimulation of phospholipase C activity (pK(i) = 9.22) in sst(3)-transfected CCL39 cells. [(125)I-Tyr(7)]sst(3)-ODN-8 selectively labels sst(3)-expressing cells with subnanomolar binding affinity (K(D) = 0.27 nM). With the use of this radioligand, sst(3)-expressing human tumors, particularly inactive pituitary adenomas, can be identified with receptor autoradiography; moreover, areas of the human lymphoreticular system express sst(3) binding sites selectively displaced by nanomolar concentrations of sst(3)-ODN-8. Based on the structure-activity relationship of selected analogs substituted at positions 3, 7, and 8, we hypothesize that the basis for sst(3) selectivity, high affinity, and possibly antagonism resides in the ring size of the analog and the unique conformational and structural character of the N-methylated amino-2-naphthoyl side chain of aminoglycine at position 8 and not in the Tyr(7) substitution or in the d-configuration at position 3. The family of labeled and unlabeled sst(3)-ODN-8 analogs represents highly innovative, potent, and specific sst(3)-selective antagonist tools for the study of sst(3)-mediated physiological and pathophysiological conditions that may suggest novel clinical applications.

Peptides as regulators of the immune system: emphasis on somatostatin

Study of the communication between nervous and immune systems culminated in the understanding that cytokines, formerly considered exclusively as immune system-derived peptides, are endogenous to the brain and display central actions. More recently, immune cells have been recognized as a peripheral source of "brain-specific" peptides with immunomodulatory actions. This article reviews studies concerning reciprocal effects of selected cytokines and neuropeptides in the nervous and immune systems, respectively. The functional equivalence of these two categories of communicators is discussed with reference to the example of the actions of neuropeptide somatostatin in the immune system.

Somatostatin analog SMS 201995 inhibits proliferation in human leukemia T-cell line: relevance of the adenylyl cyclase stimulation

Octreotide SMS 201995 is a stable somatostatin (SRIF) analog with potent antiproliferative actions in numerous cell types including normal T lymphocytes. It is currently used in the clinical treatment of different malignancies. However, the possible beneficial actions of octreotide in T-cell leukemia have not been addressed before, although these cells express SRIF receptors. For instance, human leukemia Jurkat T cells have been shown to express a single SRIF receptor isotype: sst3 that can be pharmacologically targeted by octreotide. In this study, we therefore studied SMS 201995 effects on in vitro [(3)H-CH3]thymidine incorporation in Jurkat T cells. Our data show that octreotide inhibits the proliferation of Jurkat cells both in the absence and in the presence of mitogens. By contrast, SRIF28, an endogenous SRIF analog sharing with SMS 201995 an almost identical affinity for somatostatin sst3 receptors, increases [(3)H-CH3]thymidine uptake in both mitogen-activated and nonactivated cells. To assess the mechanisms of the opposite actions of these two analogs on leukemia T-cell proliferation, we next studied their effects on adenylyl cyclase activity in whole Jurkat cells. At least in the presence of mitogens, SMS 201995 significantly enhances the adenylyl cyclase activity whereas SRIF28 inhibits it. Taken together these data are in accordance with the current hypothesis according to which increase and decrease in cAMP production are required to allow the inhibition and stimulation of T-cell proliferation, respectively. They also point to a potential therapeutic benefit of SMS 201995 in the management of human T-cell leukemia.

Somatostatin inhibits follicle-stimulating hormone-induced adenylyl cyclase activity and proliferation in immature porcine Sertoli cell via sst2 receptor

The potential involvement of somatostatin (SRIF) in testicular function was studied by using as a model primary cultures of purified immature porcine Sertoli cells. In the present report we show that Sertoli cells express mRNA for sst2 SRIF receptor and display SRIF-sensitive adenylyl cyclase. Sensitivity of adenylyl cyclase to SRIF and its analogues is compatible with the pharmacological profile of this receptor type. Relevant cAMP production is similarly inhibited by SRIF in both basal and stimulated (by gonadotropin FSH or by forskolin) conditions. Moreover, the observed SRIF actions on Sertoli cells require functional coupling of specific membrane receptors to adenylyl cyclase via Gi proteins because pertussis toxin prevents SRIF-dependent inhibition of adenylyl cyclase in either basal or FSH-stimulated conditions. Given the potent antiproliferative actions of SRIF in other cell types, we further assessed the possible SRIF-dependent modulation of [(3)H]thymidine incorporation by Sertoli cells. Our data point to SRIF-mediated inhibition of both basal and FSH-stimulated [(3)H]thymidine uptake. This inhibition of Sertoli cell proliferation is, at least in basal conditions, also blocked by pertussis toxin pretreatment. Altogether, these data suggest that SRIF may play a role as an (local) inhibitor of FSH actions in testicular development.

Evidence for a selective loss of somatostatin receptor subtype expression in male germ cell tumors of seminoma type

Somatostatin (SRIF) is a potent antiproliferative signal for both normal and tumoral mammalian cells and an alteration in the SRIF receptor expression pattern has been associated with carcinogenesis. In the present study, the relevance of SRIF signaling to human male germ cell tumors was assessed at the receptor level. The expression of five SRIF receptor (sst1-sst5) mRNAs was estimated by RT-PCR and compared between normal and tumoral testes. All 12 normal testicular tissues studied contained sst3 and sst5 receptor transcripts whereas sst4 was present in almost all (11 of 12). sst1 transcripts were consistently absent while the majority (11/12) of normal samples studied did not contain sst2 mRNA. Parallel assessment of SRIF receptor mRNAs in 10 seminoma testicular germ cell tumors showed expression of a single receptor type, sst5, in all samples analyzed. All seminoma samples were depleted in transcripts corresponding to sst1 and sst2 receptors while either sst3 or sst4 mRNAs were absent in almost all (9 of 10) tumoral samples studied. The comparison of SRIF receptor expression between normal tissue and seminoma tumors thus points to a selective loss of sst3 and sst4 mRNA expression in seminomas. Altogether these data indicate that: (i) normal human testes are putative SRIF targets; (ii) loss of sst3 and sst4 SRIF receptor expression might be associated with seminoma carcinogenesis.

Somatostatin and substance P induced in vivo by lipopolysaccharide and in peritoneal macrophages stimulated with lipopolysaccharide or interferon-gamma have differential effects on murine cytokine production

We have investigated whether lipopolysaccharide (LPS) induces substance P (SP) and somatostatin (SOM) in popliteal lymph nodes in vivo and whether macrophages are a source of SP and SOM in vitro. We have also investigated the effect of SP and SOM treatment on the production of cytokines. SP reached a maximum 3 days after injection of LPS (100 microg/footpad) and then declined. SOM expression after LPS injection reached a maximum at 5-7 days. Stimulation of thioglycolate-elicited peritoneal macrophages with LPS (20 microg/ml), recombinant interferon-gamma (rIFN-gamma, 100 U/ml), and LPS plus rIFN-gamma induced SOM and SP. Thioglycolate-elicited, unstimulated peritoneal macrophages also synthesized these peptides. SOM (10(-12)-10(-8) M) significantly inhibited IL-6 and IFN-gamma production, whereas SP at those concentrations enhanced cytokine production by activated lymphocytes and macrophages. These findings suggest that neuropeptides which originate from macrophages and nerve fibers act as immunomodulators to mediate changes in the pattern of cytokine production.

sst5 somatostatin receptor mRNA induction by mitogenic activation of human T-lymphocytes

SRIF has neuro-immunomodulatory actions on immune cells, including T-lymphocytes. Molecular mechanisms involved in these actions were studied by RT-PCR analysis of SRIF receptor expression in resting and initogen-activated human T-lymphocytes. Our results point to the mitogen-associated induction of sst5 receptor subtype. Conversely, sst3 receptor appears constitutively expressed in both activity states. Assessment of biologic actions of SRIF14 in activated T-lymphocytes indicates that, in nanomolar concentration range, this peptide moderately inhibits mitogen-induced IL-2 secretion. Nevertheless, T-lymphocyte proliferation is not inhibited in the presence of SRIF14 but is even slightly increased. Altogether these data suggest a complex mechanism of SRIF neuro-immunomodulatory actions.