Biomedical subjects

D A Weigent

Publications and source records attributed to D A Weigent.

At least 19 recordsLinked to original sources

PubMed1995

Associations between the neuroendocrine and immune systems.

Organisms respond to infection with complex adaptations involving bidirectional communication between the immune and neuroendocrine systems. The idea of intercellular communication between the neuroendocrine and immune systems via common signal molecules has provided a conceptual framework for such crosstalk. The studies to date show that cells of the immune system contain receptors for neuroendocrine hormones and can also be considered a source of pituitary and hypothalamic peptides. The structure and pattern of synthesis of these peptides by leukocytes appear similar to neuroendocrine hormones, although some differences exist. Once secreted, these peptide hormones may function as endogenous regulators of the immune system as well as conveyors of information from the immune to the neuroendocrine system. The plasma hormone concentrations contributed by lymphocytes usually do not reach the levels required when the pituitary gland is the source, but because immune cells are mobile, they have the potential to locally deposit the hormone at the target site. Likewise, other studies show that cells of the neuroendocrine system contain receptors for cytokines and can also be considered a source of cytokines, particularly interleukin-1 (IL-1) and IL-6. In the pituitary IL-1 beta coexists with thyroid stimulating hormone in a subpopulation of thyrotropes, suggesting it may have a role as a pituitary paracrine factor. The cytokines, including IL-1, IL-2, IL-6, interferon-gamma, and tumor necrosis factor, exert profound effects on hypothalamic pituitary axes. It is our hypothesis that the relay of information to the neuroendocrine system represents a sensory function for the immune system wherein leukocytes recognize stimuli that are not recognizable by the central and peripheral nervous systems (i.e., bacteria, tumors, viruses, and antigens). The recognition of such noncognitive stimuli by immunocytes is then converted into information and a physiological change occurs. Future studies into the physiological role that cytokines and neuroendocrine hormones have in these systems will be of considerable interest for both immunologists and endocrinologists.

Animals↗

PubMed1992

The production of growth hormone and insulin-like growth factor-I by the same subpopulation of rat mononuclear leukocytes.

In the present study, we evaluated the subpopulation of lymphoid cells from normal and hypophysectomized rats producing GH and IGF-I in vitro. The data show that removal of the pituitary results in depression of GH production in spleen, thymus, and bone marrow and an increase in the peripheral blood leukocytes. The changes in the percentage of cells producing GH in hypophysectomized animals are not due to a single cell type but appears to influence the T-helper, T-cytotoxic, and B-cell subsets. Interestingly, no significant changes in the levels of GH RNA were detected between control and hypophysectomized animals after the in vitro culture. We also found that the increase in GH production in spleen cell cultures after mitogen stimulation could be accounted for by an increase in the percentage of T cells producing GH. Lastly, we demonstrated that the cells positive for GH production were also positive for IGF-I production. This later finding coupled with our previous results suggest that an autocrine regulatory circuit may be important for the production of leukocyte-derived irGH and irIGF-I within the immune system.

Animals↗

PubMed1991

The production of growth hormone by subpopulations of rat mononuclear leukocytes.

In this study we analyzed the production of GH mRNA and secretion of GH by purified subpopulations of rat lymphoid cells. The data demonstrate that mononuclear leukocytes from various tissues, including spleen, thymus, bone marrow, Peyer's patches, and peripheral blood, all have the ability to produce GH mRNA and secrete GH. Data obtained with cells separated by adherence, nylon wool columns, and positive and negative sorting with monoclonal antibodies that define B, monocyte, T helper and T cytotoxic cells show that several different cell types have the ability to produce GH mRNA. The results suggest that B cells, macrophages, and T helper cells produce more GH mRNA and protein than that of T cytotoxic cells. Natural killer (NK) cells also produce detectable levels of GH mRNA and protein. To validate that leukocyte GH RNA produced in vitro was similar in structure to pituitary GH RNA, we studied the RNA by reverse transcription and the polymerase chain reaction. A sample of the PCR reaction products, analyzed by gel electrophoresis, showed a single major DNA band corresponding in length (600 base pairs) to the distance between the 5' ends of the two GH-specific primers. The DNA band was specifically labeled with a GH-specific probe after Southern transfer to nitrocellulose. Leukocyte GH purified by immunoaffinity chromatography from culture fluids was shown to be bioactive based on its ability to stimulate the incorporation of tritiated thymidine in primary rat spleen cell cultures. The bioactivity could be blocked with specific antibodies to rat GH. Taken together, the data suggest that there is heterogeneity within lymphocytes regarding their ability to produce GH and are consistent with the idea that GH may be active in local immune responses.

Animals↗

PubMed1991

Growth hormone releasing hormone receptors on thymocytes and splenocytes from rats.

In the present study, we determined that rat mononuclear leukocytes possess specific receptors for growth hormone releasing hormone (GHRH). The results show that the binding of 125I-labeled GHRH to spleen and thymic cells was saturable and of a high affinity, approximately 3.5 and 2.5 nM for thymus and spleen cells, respectively. The Scatchard analysis revealed a binding capacity of approximately 54 and 35 fmol per 10(6) cells on thymus and spleen, respectively. The binding of GHRH was not competed by 10(-6) M growth hormone, corticotropin releasing factor, substance P or luteinizing hormone releasing hormone and vasointestinal peptide (VIP). Partial characterization of the receptor was accomplished by crosslinking 125I-labeled GHRH to thymus cells with disuccinimidyl suberate and polyacrylamide gel electrophoresis. Autoradiography of dried gels showed two major components in leukocytes and pituitary cells at approximately 42 and 27 kDa which could be diminished by unlabeled GHRH. The treatment of leukocytes with GHRH (10 nM) rapidly increased the intracellular free calcium concentration from a basal level of 70 +/- 20 nM to a plateau value of 150 +/- 20 nM in 6 min after stimulation. The functional activity of GHRH receptors was studied further by measuring lymphocyte proliferative responses and the increase in the level of cytoplasmic GH RNA. The presence of GHRH alone resulted in a dose-dependent increase in thymidine and uridine incorporation and a dose-dependent increase in the levels of GH RNA in the cytoplasm. Taken together, the results show that lymphocytes contain specific receptors for GHRH that are coupled to important biological responses and further support the concept of bidirectional communication between the immune and neuroendocrine tissues.

Animals↗

PubMed1991

Expression of immunoreactive growth hormone in leukocytes in vivo.

In the present study, we investigated the production of growth hormone (GH)-related RNA and protein in vivo by rat leukocytes after intraperitoneal treatment with different inducing agents including bacterial lipopolysaccharide (LPS) and Freund's complete adjuvant (FCA). The data showed that in rats after exposure to LPS or FCA leukocytes obtained from the spleen, thymus, and peritoneum all showed a dose-dependent increase in GH-related RNA content. The peak production of GH-related RNA was observed 48 h after treatment in the spleen and thymus and 96 h after treatment in the peritoneum. We also evaluated the ability of LPS-sensitive (C3HeB/FeJ) and resistant (C3H/HeJ) inbred mice treated with LPS to produce GH-related RNA. The LPS-sensitive mice presented with a typical pathophysiologic response pattern and higher levels of GH-related RNA in the spleen and thymus than the LPS-resistant mice. An increase in the production of immunoreactive GH (irGH) was also observed by direct immunofluorescence with specific antibodies to rat GH. We validated that the GH-related RNA produced in vivo by leukocytes was similar in structure to pituitary GH RNA using reverse transcription and the polymerase chain reaction (PCR). A sample of the PCR reaction, analyzed by gel electrophoresis, showed a single major DNA band corresponding in length (600 base pairs) to the distance between the 5'-ends of the two GH-specific primers that was specifically detected with a GH-specific probe after Southern transfer. In other studies with normal nontreated animals, the GH RNA levels are higher in the evening hours and early on in the first month of life. Taken together, our data are the first demonstration that GH RNA and immunoreactive protein can be detected in leukocytes in vivo both in normal and stimulated animals and support the idea that GH may be active in an immune response.

Animals↗

PubMed1991

An antisense oligodeoxynucleotide to growth hormone messenger ribonucleic acid inhibits lymphocyte proliferation.

The role of GH in lymphocyte proliferation was studied by examining the effect of an antisense oligodeoxynucleotide (ODN) complementary to GH mRNA. The results of these studies showed that antisense GH ODN treatment inhibits lymphocyte production of immunoreactive GH (irGH). Lymphocytes treated with the GH antisense ODN produced less irGH than did lymphocytes treated with control sense GH ODN. Antisense GH ODN-mediated inhibition of irGH production resulted in a decrease in lymphocyte proliferation. Cells with the antisense GH ODN had less (87%) incorporation of [3H]thymidine [( 3H]TdR) in both resting and Concanavalin-A-stimulated lymphocytes, whereas the incorporation of [3H]TdR in cells treated with a control ODN was not significantly affected. The effect of the antisense ODN on [3H]TdR incorporation was specific, since it could be reversed by hybridization competition with a complementary GH sense ODN or by the addition of exogenous rat GH. Collectively, the data indicate that lymphocytes synthesize and secrete irGH and that irGH produced by these cells can stimulate proliferation, suggesting that GH may play an autocrine/paracrine role in lymphocyte replication.

Animals↗

PubMed1991

Characterization of immunoreactive insulin-like growth factor-I from leukocytes and its regulation by growth hormone.

In the present study, we investigated the production of insulin-like growth factor I (IGF-I) by leukocytes and its production after treatment with GH. Immunoreactive (ir) IGF-I was observed in leukocytes by direct immunofluorescence with fluorescein isothiocynate-conjugated antibodies to IGF-I. Studies using immunoaffinity purification, HPLC and a fibroblast proliferation bioassay suggests that the de novo synthesized leukocyte-derived irIGF-I is similar in mol wt, antigenicity, and bioactivity to serum IGF-I. We also evaluated the effect of GH on the production of leukocyte-derived irIGF-I. Spleen cells cultured for 24 h in the presence of exogenous GH caused a 2-fold elevation of irIGF-I as demonstrated by RIA and immunofluorescence. In order to determine if leukocyte-derived irGH can stimulate the production of irIGF-I, we cultured spleen cells for 24 h in the presence of antibodies specific for GH. The data showed a decrease in the number of cells positive for irIGF-I, suggesting that leukocyte-derived irGH may stimulate the synthesis of irIGF-I by leukocytes. We also demonstrated that exogenous IGF-I can decrease the levels of leukocyte GH-related RNA and ir protein. Taken together, our data demonstrate the synthesis and secretion of bioactive irIGF-I from leukocytes and suggest a regulatory circuit for leukocyte-derived irGH and irIGF-I within the immune system.

Animals↗

PubMed1991

Detection of growth hormone and growth hormone-releasing hormone-related messenger RNA in rat leukocytes by the polymerase chain reaction.

To validate that growth hormone (GH) and growth hormone-releasing hormone (GHRH) can be produced by leukocytes, we have assessed the presence of GH and GHRH-related mRNA in leukocyte cultures by reverse transcription and the polymerase chain reaction. A sample of the polymerase chain reactions were size-fractionated by electrophoresis in a 0.8% agarose gel and examined with ultraviolet light after ethidium bromide staining. Single major DNA bands corresponding in length to the distance between the 5' ends of the two GH and GHRH specific primers, 603 base pairs and 260 base pairs, respectively, were obtained. The DNA bands hybridized specifically to GH- and GHRH-specific probes after Southern transfer to nitrocellulose. The identity of the GH polymerase chain reaction material was confirmed by restriction enzyme analysis. The results showed that GH and GHRH gene expression occurs in mononuclear leukocytes and support the idea that these neuroendocrine hormones may be common signal molecules between the immune and neuroendocrine systems.

Animals↗

PubMed1990

Bidirectional communication between the neuroendocrine and immune systems. Common hormones and hormone receptors.

The results reviewed here support a molecular basis for bidirectional communication between the immune and neuroendocrine systems. The main findings can be summarized as follows: First, cells of the immune system can synthesize biologically active neuroendocrine peptide hormones. Second immune cells also possess receptors for many of these peptides. Third, these same neuroendocrine hormones can influence immune function; and fourth, lymphokines can influence neuroendocrine tissues. The interesting conceptual advance is the idea that the immune system may serve as a sensory organ. Thus, the immune system may sense stimuli that are not recognized by the central or peripheral nervous system. These stimuli are termed noncognitive and include bacteria, viruses, tumors and antigens. The recognition of such stimuli is converted into information in the form of lymphokines, monokines, and hormones and a message received by neuroendocrine tissues. On the other hand, nervous system recognition of stimuli can also be converted into chemical signals that can be relayed to immune cells resulting in physiological changes. On this basis, we predict that the pathophysiology associated with infectious agents may be related to the types and amounts of hormones produced by the immune system.

Animals↗

PubMed1989

Expression of growth hormone by lymphocytes.

In the present study, we evaluated whether mononuclear leukocytes could synthesize and secrete growth hormone (GH) in vitro. Studies using antibody affinity chromatography, high pressure liquid chromatography, and polyacrylamide gel electrophoresis indicate that leukocytes secrete a approximately 22,000 dalton molecular weight immunoreactive GH (irGH). The irGH appeared to be de novo synthesized since it could be radiolabeled with tritiated amino acids and its production blocked by prior incubation of leukocytes with cycloheximide. The levels of secreted irGH were enhanced by concanavalin A or lipopolysaccharide. By using RNA slot blot analysis, we detected specific GH mRNA present in the cytoplasm of rat leukocytes. Leukocytes from a variety of tissues in rats, including spleen, thymus, bone marrow, and peripheral blood as well as separated spleen T and B cells, were all observed to produce GH RNA and secrete GH from the cells. We conclude that lymphocytes produce a mRNA for irGH and are then able to translate that message and secrete the molecule from the cell. The data suggest a potential regulatory loop between the immune and neuroendocrine systems.

Animals↗

PubMed1989

Hormones common to the neuroendocrine and immune systems.

Considerable progress is now being made in studies of the interactions between the immune and neuroendocrine systems, and the relevance of the results to many disease processes is increasingly recognised. Recent published, and hitherto unpublished, work on one aspect of this topic--the production and function of neuroendocrine hormone by cells of the immune system--is herein summarised by a foremost investigator and his colleagues. Evidence is presented that several peptide hormones (ACTH, endorphins, thyrotropin, chorionic gonadotropin, growth hormone) are produced constitutionally, or in response to stimulation, by cells of the immune system, and there is speculation as to their roles in local immune response, endotoxic shock, antibody production, pregnancy, and in the diagnosis of specific psychiatric and neuroendocrine disorders. The review and commentary contribute to fuller understanding of the underlying molecular biology, from which new opportunities in rational drug design will undoubtedly emerge.

Animals↗

PubMed1988

Production of immunoreactive growth hormone by mononuclear leukocytes.

In the present study, we evaluated whether mononuclear leukocytes could synthesize and secrete growth hormone (GH) in vitro. By using RNA slot blot analysis, we detected maximum spontaneous levels of specific GH mRNA in the cytoplasm of rat leukocytes after a 4-h incubation. Northern gel analysis demonstrated that the specific leukocyte GH RNA was polyadenylated and had a molecular mass of 1.0 kb. Further studies using immunofluorescence, antibody affinity chromatography, and Sephacryl gel filtration indicate that leukocytes secrete a high molecular weight (greater than 300,000) and a low molecular weight (approximately 22,000) immunoreactive GH (irGH). A substantial amount of the high molecular weight irGH can be converted to the lower molecular weight form after reduction with mercaptoethanol. The irGH appeared to be de novo synthesized because it could be radiolabeled with tritiated amino acids and its production could be blocked by previous incubation of leukocytes with cycloheximide. The replication of Nb2 rat node lymphoma cells was stimulated by affinity-purified human lymphocyte-derived irGH. The growth stimulation was blocked by specific antibodies to hGH. We conclude that lymphocytes produce an irGH that is similar to if not identical to pituitary GH in terms of bioactivity, antigenicity, and molecular weight. The findings demonstrate a potential regulatory loop between the immune and neuroendocrine tissues.

Animals↗

PubMed1988

Individuals infected with HIV possess antibodies against IL-2.

Studies are presented here which demonstrate that antibodies reacting with human interleukin-2 (IL-2) are present in the sera of patients infected with the human immunodeficiency virus (HIV). It is likely that these antibodies are present due to a homology between the HIV envelope protein and IL-2. The homologues are six amino acids in length corresponding to the carboxy terminus of gp41, Leu-Glu-Arg-Ile-Leu-Leu (LERILL), and residues 14-19 of secreted IL-2, Leu-Glu-His-Leu-Leu-Leu (LEHLLL). Thus, we questioned whether antibodies made against this HIV envelope peptide would cross-react with IL-2. Not only do a high percentage of the HIV-infected individuals tested here have antibodies against LERILL, but these antibodies cross-react with the IL-2 sequence, LEHLLL. Additional antigenic processing of IL-2 is suggested by the finding that epitopes other than this sixmer are also recognized by antibodies in patients' sera. Thus, these studies suggest a mechanism by which infection with HIV can induce a potentially suppressive autoimmune response. Specifically, antibodies against an HIV envelope peptide cross-react with an epitope in IL-2.

Acquired Immunodeficiency Syndrome↗

PubMed1987

Antibodies to the carboxyl terminus of mouse interferon-gamma neutralize its immunoregulatory and antiviral activities.

Antibodies to a synthetic carboxy-terminal peptide (Cys-Ser-Leu-Arg-Lys-Arg-Lys-Arg-Ser-Arg-Abu) (gamma-C-TP) of mouse interferon-gamma (MuIFN-gamma) were produced in rabbits. They neutralized the antiviral activity of MuIFN-gamma but not that of MuIFN-alpha/beta or human (Hu) IFN-alpha/beta or -gamma. They also inhibited the IFN-dependent enhancement of natural cytotoxic cells (NCC) and the in vivo plaque-forming cell (PFC) response to sheep red blood cells (SRBC). Thus, our results indicate that polyclonal antibodies specific for the nine carboxy-terminal amino acids of MuIFN-gamma can specifically inhibit the antiviral and immunoregulatory activities of this IFN in vitro. In addition, our findings indicate that endogenous production of MuIFN-gamma in vivo plays a role in development of the full antibody response to SRBC surface antigens.

Animals↗

PubMed1987

Interferon review.

Although IFN proteins were recognized first for their potent antiviral properties, it has now been established that they may profoundly affect other vital cellular functions. The IFNs are divided into three main classes, alpha, beta, and gamma, and are defined by their differences in amino acid sequences, physicochemical properties, and induction by different agents from different cell types. The inducing agents include viruses, bacteria, bacterial products, polymers, low molecular weight compounds, and antigens or mitogens. Studies on the mechanisms of action of IFNs have mainly been focused on their antiviral actions. However, many of the facts revealed by these studies are equally relevant for understanding other actions of IFN. IFNs are extremely potent, they interact with specific receptors, and they induce the expression of specific genes, the products of which mediate their various actions. There is almost a complete lack of knowledge of what happens between the interaction of IFN with its receptor and induction of new RNA synthesis. However, we are beginning to understand how some of the IFN-inducible enzymes impair viral replication. The discovery of the dsRNA-dependent enzymes has implications beyond the IFN system. It is quite possible that they are used for other physiologic regulatory systems as well. The identities and functions of many other IFN-inducible proteins remain to be elucidated. Principally, IFNs alpha and beta are cytokines in that they may be produced by the cellular components of the immune system and have immunoregulatory effects on the cells of the immune system. These effects include enhancement of surface structures such as histocompatibility antigens, pleiotropic hormone-like effects, and stimulation or inhibition of the activities of a number of different effector cells such as B cells, T cells, macrophages, and natural killing cells. IFN levels may be below detection and yet mediate important biologic functions. Perhaps the most interesting IFN subtype regarding immunoregulation is IFN gamma, which is a product of T lymphocytes. Few drugs have stimulated as much research interest or clinical promise as the IFNs. Clinical trials in patients have shown most promise in coryza, herpes virus infections, papilloma virus tumors, hairy cell leukemia, multiple myeloma, and renal cell carcinoma. IFN gamma employed alone and in combination with IFN alpha may dramatically increase IFN's activity. IFN treatment combined with chemotherapy also may give enhanced antitumor activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1987

Interactions between the neuroendocrine and immune systems: common hormones and receptors.

The studies reviewed here support a molecular basis for bidirectional communication between the immune and neuroendocrine systems. The main findings can be summarized as follows: First, cells of the immune system can synthesize biologically active neuroendocrine peptide hormones. Second, immune cells also possess receptors for many of these peptides. Third, these same neuroendocrine hormones can influence immune function; and fourth, lymphokines can influence neuroendocrine tissues. Although recent studies have begun to unravel the biochemistry of bidirectional communication between the immune and neuroendocrine systems, there are still missing parts in this puzzle. Among the important questions that must be resolved are the identification of factors that trigger the synthesis of neuroendocrine hormones by immune cells. Are these events operating similar to or in balance with pituitary cells? Drugs that interfere with either pathway may be useful. Second, it will be of value to understand the factors controlling neuroendocrine hormone receptor expression on immune cells. A better understanding of the spectrum of positive and negative regulatory events for both systems may determine the ultimate behavior of immune and neuroendocrine cells. In addition, since leukocytes can produce hormones and also have receptors for the same hormones (e.g., ACTH and GH), it is possible that these immunocytes may also influence their own function in an autocrine-like fashion. We have postulated that the immune system can serve as a sensory organ for external stimuli that cannot be detected by the nervous system (Blalock 1984). Thus, the immune system recognizes stimuli such as bacteria, viruses or tumors, whereas the nervous system detects classical sensory stimuli. The contribution of extrapituitary sites of hormone production and function may provide new clues to define psychological and/or pathological states in the pathophysiology of infectious diseases and tumors.

Animals↗

PubMed1986

The HTLV-III envelope protein contains a hexapeptide homologous to a region of interleukin-2 that binds to the interleukin-2 receptor.

A region of human interleukin-2 (IL-2) which was predicted to be a contact point with its receptor was used to locate a homologous region in the envelope protein of human T-lymphotropic retrovirus (HTLV-III). This homologous six amino acid peptide from the carboxy (C)-terminus of the HTLV-III envelope protein was found to inhibit the biological activity of human IL-2 in a murine spleen cell proliferation assay. When conjugated to a carrier protein, this peptide inhibited the binding of radiolabelled IL-2 to its receptor. The biological activity of the peptide was antagonized by a six amino acid peptide fragment of the IL-2 receptor which was predicted to be the contact point on the receptor that corresponded to the binding region of IL-2. The HTLV-III peptide also inhibited the binding of radiolabelled IL-2 to polyclonal anti-IL-2 antiserum. These data support the previous assignment of contact points between IL-2 and its receptor. They also suggest two possible mechanisms of immunosuppression during acquired immunodeficiency syndrome (AIDS). One involves direct competition of the envelope protein or its fragments with IL-2 for binding to the IL-2 receptor. The other involves antibodies to the envelope protein which crossreact with and neutralize IL-2.

Amino Acid Sequence↗

PubMed1986

Pretreatment of human lymphocytes with interferon enhances the synthesis of interferon in cocultures with allogeneic cells.

Human lymphocytes pretreated with interferon (IFN) alpha, beta, or gamma produced 17 times more IFN alpha (600-10,000 units/ml) than nontreated lymphocytes when cocultivated with allogeneic cells. Significant increases in IFN production (500-3,000 units/ml) were observed when lymphocytes were treated with IFN for just 2 h, and peak levels (10,000 units/ml) were produced after a 4-h treatment. The amount of IFN required to show the maximum priming effect was between 100 and 1,000 units; higher levels of IFN were inhibitory. The levels of IFN increased as the lymphocyte-to-target-cell ratio increased from 2:1 to 10:1 and decreased at higher ratios. The decrease in IFN production at higher ratios of lymphocytes to target cells could not be attributed to the presence of a soluble suppressor substance. The additional IFN found in supernates was attributed to enhanced production of IFN by the same cells, rather than recruitment of more cells to produce IFN. This conclusion is based on the fact that no increase in the number of cells staining positive for IFN production was observed in primed lymphocytes. The increased amount of IFN due to priming enhanced both nonsensitized cytotoxic activity and the transfer of antiviral activity, which could be prevented by antibody to IFN. The data suggest that priming may be an important biological mechanism for obtaining significant levels of IFN more rapidly in the vicinity of transformed cells or virus-infected tissues.

Cells, Cultured↗