Influence of beta-endorphin on phytohemagglutinin-induced lymphocyte proliferation and on the expression of mononuclear cell surface antigens in vitro

Immunology, signal transduction, and behavior in hypothalamic-pituitary-adrenal axis-related genetic mouse models

A classical view of the neuroendocrine-immune network assumes bidirectional interactions where pro-inflammatory cytokines influence hypothalamic-pituitary-adrenal (HPA) axis-derived hormones that subsequently affect cytokines in a permanently servo-controlled circle. Nevertheless, this picture has been continuously evolving over the last years as a result of the discovery of redundant expression and extended functions of many of the molecules implicated. Thus, cytokines are not only expressed in cells of the immune system but also in the central nervous system, and many hormones present at hypothalamic-pituitary level are also functionally expressed in the brain as well as in other peripheral organs, including immune cells. Because of this intermingled network of molecules redundantly expressed, the elucidation of the unique roles of HPA axis-related molecules at every level of complexity is one of the major challenges in the field. Genetic engineering in the mouse offers the most convincing method for dissecting in vivo the specific roles of distinct molecules acting in complex networks. Thus, various immunological, behavioral, and signal transduction studies performed with different HPA axis-related mutant mouse lines to delineate the roles of beta-endorphin, the type 1 receptor of corticotropin-releasing hormone (CRHR1), and its ligand CRH will be discussed here.

Increased splenocyte proliferative response and cytokine production in beta-endorphin-deficient mice

We used beta-endorphin-deficient mice as a novel approach to confirm the physiological role that opioid peptides play in the development or regulation of the immune system. We found that mice lacking beta-endorphin possessed an enhanced immune response, measured in terms of splenocyte proliferation and interleukin (IL)-2 mRNA levels, in vitro production of the splenic macrophage inflammatory cytokines IL-6 and Tumor Necrosis Factor (TNF)-alpha and plasma IL-6 following lipopolysaccharide (LPS) administration. beta-Endorphin-deficient mice had attenuated increases of plasma ACTH and corticosterone levels in response to LPS. These results are consistent with a postulated inhibitory role of endogenous beta-endorphin on the immune system at multiple levels.

Short-term changes in the immune system of elite swimmers under competition conditions. Different immunomodulation induced by various types of sport

This study was designed to investigate changes in the immune system of elite swimmers compared with well-conditioned age- and sex-matched controls in relation to a competition swim (field study). Furthermore, the aim was to reveal possible differences in immune system changes depending on the type of sport performed by comparing with an earlier study of similar design, from the same laboratory that tested elite runners in relation to a competition run. The swimmers were tested before, immediately after and 2 h and 24 h after a competition swim. Lymphocyte subsets (CD5, CD3, HLA-DR, CD4, CD8, CD19, CD3/CD16+56, CD57, CD18, CD16/CD122) all increased after the run, decreased to normal or subnormal levels after 2 h, and returned to normal after 24 h (absolute numbers). The findings were identical for the swimmers and the age- and sex-matched control group. No change in polymorphonuclear granulocyte migration was found. The lymphocyte proliferative responses decreased 2 h after the exercise. No changes were seen in plasma cytokine levels (interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-alpha) in relation to exercise, but significantly lower baseline values for IL-6 were observed in the swimmers. An increase in total natural killer cell activity immediately after exercise, followed after 2 h by a decrease, was seen in both swimmers and controls. Finally, no complement activation was detected. Compared with an earlier study of elite runners, differences were seen in granulocyte chemotactic response, TNF-alpha plasma activity and the lymphocyte proliferative response to mitogen. These differences might be explained by the degree of immune system activation following muscle damage during exercise, inducing an increase in cytokines, which are known to activate and modulate both lymphocytes and granulocyte function. Our findings demonstrate identical exercise-induced, immune system changes in elite swimmers and well conditioned controls, and furthermore, the findings suggest that different types of sport performed at maximum intensity induce different immune system changes.

Positive and negative immunomodulation by opioid peptides

The data that follow review part of the existing evidence concerning the neuroimmune functions mediated by opioid peptides, with particular regard to dual immunomodulatory effects. Limited references to substances other than opioid peptides are included, mainly to emphasize the possible similarities in the mediation of neuroimmune interactions by different informational substances, while the interactions directed from the immune to the nervous system have deliberately been omitted.

Expression of naloxone-resistant beta-endorphin binding sites on A20 cells: effects of concanavalin A and dexamethasone

beta-Endorphin affects mononuclear cell proliferation, cytokine production and calcium uptake in a naloxone-resistant manner. The presence of naloxone-insensitive binding sites for beta-endorphin have been demonstrated on murine EL4-thymoma cells, transformed human mononuclear cells and normal murine splenocytes. Since murine splenic B cells have been shown to express naloxone-resistant receptors for beta-endorphin in response to the mitogen, concanavalin A (Con A), the A20 B-cell lymphoma line was used to further study regulation of this site by Con A and dexamethasone. Analyses showed two sites: a high-affinity site, Kd1 = (8.7 +/- 2.3) x 10(-11) M and binding capacity (Bmax1) of (2.6 +/- 2.0) x 10(3) receptors/cell; and a low-affinity site, Kd2 = (2.2 +/- 0.8) x 10(-8) M with Bmax2 of (1.5 +/- 0.8) x 10(5) receptors/cell. Competition studies showed that N-acetyl-beta-endorphin was approx. 5-fold and beta-endorphin6-31 10-fold less potent than beta-endorphin1-31. Neither beta-endorphin1-27 nor naloxone, morphine or other opioid receptor agonists displaced [125I]beta-endorphin. Con A (20 micrograms/ml) significantly increased the Bmax (3.5-fold; expressed per cell) and resulted in a loss of the higher-affinity site. However, the increased Bmax occurred in proportion to the Con-A-induced increase in protein/cell. Dexamethasone (Dex) also increased Bmax, primarily by increasing (2-3-fold) the number of lower affinity sites. In contrast to Con A, two binding sites persisted after treatment with Dex, which exerted a minimal effect on protein/cell. Therefore, binding/cell and binding/protein/cell were both significantly enhanced by Dex. The combined effects of Dex and Con A on binding failed to show additivity or synergy. When binding was analyzed per protein/cell, the effect of Con A appeared to dominate; the Dex-enhanced binding/protein/cell was no longer evident in the presence of Dex plus Con A. Thus, Dex and Con A may enhance binding by independent mechanisms.

Immunomodulating effect of met-enkephalin on different stages of lymphocyte proliferation induced with concanavalin A in vitro

Met-enkephalin (ME) in the range of concentrations 10(-15) M to 10(-9) M has exhibited an immunomodulating effect on concanavalin A (Con A) induced proliferation of mice lymphocytes from lymph nodes in vitro. The effect of ME was shown to vary with the stage of lymphocyte activation and to depend on the mitogen dose. In the case that ME and Con A were injected simultaneously, at the zero time of proliferation, maximum inhibition was observed on the first and fourth days. In an other set of experiments when ME was added at intervals of 4 hours before measuring the proliferation response value, both inhibition (after 24 hours of proliferation) and stimulation (after 28 and 96 hours) were observed. Opioid ligands of various classes were found to act in the same manner as ME. Naloxone was shown to block the immunomodulating effect of opioids.

Immunology of the testicular excurrent ducts

The sperm autoantigen concentration in the epididymis equals or exceeds that in the testis. This makes the epididymis a probable site of initiation of an antisperm autoimmune response. The mechanisms regulating antisperm antibody formation in the testicular excurrent ducts and some related aspects with clinical interest are reviewed.

Role of central nervous system and behaviour in the immune response

Recent advances in antigen preparation and delivery have led to a renewed interest in vaccination to control infectious disease. However, relatively less attention has been devoted to host factors which affect the outcome of immune responses. There is now increasing acceptance that the central nervous and immune systems interact, and that this can be a bidirectional process. A range of behavioural and psychological states, learned responses and reactions to external stimuli have all been implicated in immune modulation. These interactions may occur via the direct innervation of lymphoid compartments, by paracrine means through the release of mediators from nerves situated in close proximity to cells involved in immunity, or by neuroendocrine signals in the form of hypothalamic, pituitary and peripheral endocrine hormones. These effects may account to some extent for unexplained variability in response to vaccination and disease challenge, through inherited or acquired differences in neuroendocrine or neurotransmitter responses to stress, circadian effects or learned behavioural responses. This review addresses the effects of environmental stimuli and behavioural manipulations on immune outcome and the response to vaccination, and the potential for practical application of these techniques in human and animal disease control and health management.

Regulation of beta-endorphin receptor expression in mouse spleen cells with Con A and rIL-2

The expression of the beta-endorphin receptor on both activated and unstimulated mouse spleen cells was studied. Results showed that unstimulated cells have only one type of beta-endorphin receptor with a specific low affinity (Kd = 1.034 +/- 0.0237 x 10(-7) M, 25,000 sites/cell). After Con A stimulation, cells express two types of receptors, one with a low affinity (Kd = 1.034 +/- 0.024 x 10(-7) M, 320,000 sites/cell) and the other with a high affinity (Kd = 1.052 +/- 0.033 x 10(-9) M, 49,000 sites/cell). The kinetic experiments during 4 days after Con A activation indicated that the receptor of high affinity emerged from 24 to 72 h, while the low affinity one increased in number after stimulation. The receptor numbers of both high and low affinity ones reached a maximum peak at 72 h, then began to decline. The addition of exogenous rIL-2 depressed the Con A-induced increment of the receptor numbers of both the high and low affinity ones, but enhanced the proliferative response of the cells. It is suggested that the degree of the expression of the receptors does not simply depend on the mitogenic degree of the cells. In addition, our experiment demonstrated that splenocytes cultured in medium with or without Con A or Con A + rIL-2 for 96 h did not secrete any detectable amount of beta-endorphin with use of the RIA assay, which is sensitive enough to detect the much lower levels of beta-endorphin than that necessary for biological effects. We suggest that the expression of the high affinity beta-endorphin receptor on the activated T-lymphocytes may have to precede the production of IL-2 to potentiate the T-cell proliferative response. The mechanisms and modes of interaction between the neuroendocrine system and the immune system were discussed.

Dynorphin blocks opioid inhibition of macrophage-colony stimulating factor-induced proliferation of bone marrow cells

We previously reported that morphine inhibits macrophage-colony stimulating factor (M-CSF)-induced proliferation of mouse bone marrow cells, both in vivo and in vitro, in a dose-dependent manner. We now report that either dynorphin A-(1-13) or dynorphin A-(1-10) amide, though having no effect on proliferation by themselves at concentrations less than 0.1 mM, can block the inhibitory effect of morphine both in vivo and in vitro, in a dose-dependent manner. The opioid antagonist naloxone can also block morphine's inhibitory effect on bone marrow cell proliferation in vivo, but has no effect in vitro. Dynorphin A-(1-13) was also able to block the dramatic reduction of spleen weight observed in animals chronically treated with morphine. Thus dynorphin, which has previously been shown to antagonize morphine analgesia, is also able to antagonize some of the immunosuppressive effects of morphine.

Chronic morphine treatment selectively suppresses macrophage colony formation in bone marrow

Opioids have been shown to have diverse effects on the immune system, both in vivo and in vitro, but their interactions on immature progenitor cells have been little studied. We have examined the effects of chronic morphine treatment of mice on colony formation by bone marrow cells in vitro. Bone marrow cells from mice implanted with morphine pellets for 72 h showed a 65% decrease in their response to macrophage colony stimulating factor (M-CSF). In contrast, chronic morphine treatment had no effect on the response of bone marrow cells to granulocyte/macrophage colony stimulating factor (GM-CSF). Removal of the morphine pellets from the mice resulted in a time-dependent reversal of the inhibition of macrophage colony formation, and the inhibition was completely blocked by simultaneous administration of naloxone and morphine pellets to the mice. No inhibition of colony formation was observed in bone marrow cells from mice treated with a single acute dose of morphine. Incubation of bone marrow cells from untreated mice for 7 days with in vitro morphine concentrations as low as 25 microM also reduced macrophage colony formation, and the opioid peptide beta-endorphin was even more potent, significantly reducing macrophage colony formation at concentrations as low as 0.25 microM. In agreement with the in vivo effects, neither opioid in vitro had a significant effect on granulocyte/macrophage colony formation. These results suggest that opioids may significantly alter the maturation of immune cells, which could result in potent effects on overall immune competence.

N-acetyl-beta-endorphin1-31 antagonizes the suppressive effect of beta-endorphin1-31 on murine splenocyte proliferation via a naloxone-resistant receptor

High affinity binding sites for beta-endorphin1-31 (beta-EP) have been observed on transformed mononuclear cells such as the human U937 monocyte-like cell line and the murine EL4-thymoma line, and on normal murine splenocytes. Binding of beta-EP at these sites is resistant to competition by naloxone and other opiate receptor ligands but sensitive to N-acetyl-beta-endorphin1-31 (N-Ac), cations and GTP-gamma-sulfate. Thus, the following studies were done to determine the functional significance of binding beta-EP and N-Ac. beta-EP suppressed phytohemagglutinin (PHA)-stimulated [3H]thymidine uptake in a dose-dependent, naloxone-insensitive fashion. beta-Endorphin1-27, (des)-tyrosine beta-endorphin2-31, or N-Ac failed to duplicate the suppressive effect of beta-EP. However, N-Ac, which is equipotent to beta-EP at displacing 125I-beta-EP bound to murine splenocytes or U937 cells, antagonized the suppressive effect of beta-EP. Taken together with previous binding studies, the present observations suggest that beta-EP effects receptor-mediated responses on normal immunocytes that do not depend on the activation of neuronal-like opiate receptors which are naloxone-sensitive. N-Ac, which shows minimal binding to such brain opiate receptors, is a potent functional antagonist of the naloxone-insensitive immunocyte receptor for beta-EP.

Beta-endorphin stimulates rat T lymphocyte proliferation

beta-Endorphin 1-31 and several structurally related peptides were tested for their ability to alter mitogen-induced T cell proliferation. Rat beta-endorphin 1-31 and human beta-endorphin 1-27 increased phytohemagglutinin (PHA)-induced [3H]thymidine incorporation into rat lymph node cells. However, when PHA-induced proliferation was suppressed by the inclusion of prostaglandin E1 (PGE1), human beta-endorphin 1-31 and a number of structurally similar peptides, including some peptides that did not alter mitogen-induced proliferation, significantly reduced the PGE1 inhibition of PHA-stimulated T cell proliferation. Although the N-terminus of beta-endorphin was necessary for potency, inclusion of the opioid antagonist naloxone together with beta-endorphin 1-31 did not alter the blockage of PGE1 inhibition of PHA-induced proliferation caused by beta-endorphin. The inhibition of mitogen-stimulated proliferation by either cholera toxin or forskolin, two additional compounds that like PGE1 also elevate cyclic AMP levels, was not blocked by beta-endorphin. Verapamil suppression of proliferation was not modified by beta-endorphin, indicating that the beta-endorphin stimulatory effect was probably not due to Ca2+ influx through verapamil-sensitive Ca2+ channels. These data suggest that beta-endorphin, acting through a nonopioid beta-endorphin receptor, may modulate immunocompetence by stimulating T cell proliferation and by counteracting the inhibitory effects of PGE1.

Restraint stress-induced elevations in plasma corticosterone and beta-endorphin are not accompanied by alterations in immune function

A variety of stressors activate the hypothalamic-pituitary-adrenal (HPA) axis, thereby resulting in elevated levels of circulating ACTH, beta-endorphin and corticosterone. Since these hormones have been shown previously to alter measures of immune function, we determined whether presentation of a stressor which activates the HPA axis produces a concomitant alteration in immune function. Restraint stress resulted in significantly elevated levels of corticosterone and beta-endorphin without affecting either proliferative or cytolytic activities of lymphocytes. At concentrations similar to those achieved during stress, in vivo, corticosterone exhibited a dose- and time-dependent reduction in both lymphocyte proliferation as well as natural killer cytotoxicity, in vitro. beta-Endorphin, on the other hand, was without direct or modulatory effects. These results indicate that restraint stress-induced activation of the HPA axis occurs without accompanying alterations in immune function.

Suppression of human B lymphocyte activation by beta-endorphin

The effects of beta-endorphin (beta-E) and contained peptides were investigated for their ability to regulate Staphylococcus aureus (SAC)-induced immunoglobulin secretion by human B lymphocytes. Co-culture of beta-E with SAC-stimulated peripheral blood-derived mononuclear cells, under serum-containing or serum-free conditions, resulted in a dose-dependent inhibition of immunoglobulin-secreting cell (ISC) formation. When the same cultures were assessed for class-specific Ig formation it was found that IgG-ISC were suppressed to a greater extent that IgA-ISC or IgM-ISC. In contrast to these results, beta-E was found to be unable to suppress SAC-induced lymphocyte proliferation. To map the suppressive activity associated with beta-E, truncated peptides based on the beta-E sequence were assessed for biological activity. The results indicated that peptides containing the N-terminal region of beta-E suppressed ISC formation. Moreover, methionine-enkephalin (beta-E 61-65) was found to be effective in suppressing ISC formation. beta-E-mediated suppression of IgG-specific ISC formation appears to involve classical receptor-ligand interaction as evidenced by the ability of naloxone to block suppression of ISC formation.

Testicular immunoregulatory factors

The present data indicate that immune cells are regulated locally in the testis by Leydig cells, Sertoli cells and resident testicular macrophages. The effects of these cells are mediated by several peptide factors, including protectin, a group of high molecular weight testicular immunosuppressive factors, and testicular interleukin-1 alpha-like factor. The testicular interleukin-1 alpha-like factor is produced by Sertoli cells and is under hypophyseal control. Its synthesis starts at puberty concomitantly with the onset of spermatogenesis and it may act as a spermatogonial growth factor. Protectin, which is under hypophyseal control, may be involved in the mechanism of prolonged transplant survival in the testicular interstitial tissue. Its levels increase at puberty. Both the testicular interleukin-1 alpha-like activity and protectin may be important in testicular pathophysiology.

Physiological basis for neuroimmunomodulation

A large number of clinical and experimental observations indicate that immune responses may be modulated by the central nervous system (CNS). The immune system (IS) and CNS are known to communicate via the endocrine and the autonomic nervous systems. In this overview, we will focus on the immunomodulating role of neurotransmitters and neuropeptides. Immune cells appear to express membrane antigens similar to those of neural cells. Similarities re-enforce analogies between CNS and IS cells. The concept that the CNS modulates immune functions implies that the immune system feeds back information to the CNS. In fact, interleukins have neuroendocrine functions whether they are produced at the periphery by immune cells or at the CNS level by glial cells. Finally, the possible endocrine functions of lymphocytes are described and it is suggested that a complete regulatory loop between immune and neuro-endocrine systems exists. Studies in neuro-immunomodulation are of great importance from a theoretical point of view, the CNS-IS inter-relationships may not be considered only between the CNS and the periphery but also at the level of the immune micro-environment which may be considered as an immune-neuro-endocrine complex.

Beta-endorphin alters a viral induced central nervous system disease in normal mice but not in nude mice

A single intracerebroventricular injection of 100 ng of beta-endorphin altered the course of the central nervous system (CNS) infection of a temperature-sensitive mutant of vesicular stomatitis virus (VSV), tsG31-KS5. When mice were administered beta-endorphin and then 24 h later infected intracerebrally with tsG31-KS5 VSV, 70% of the animals died within 8 days of infection. In comparison, less than 10% of the animals had died after 21 days when infected with tsG31-KS5 VSV alone. When mice were injected with beta-endorphin and tsG31-KS5 VSV simultaneously, or with beta-endorphin 21 days after infection, the more aggressive clinical disease was not observed. Superficially, the more lethal disease induced by beta-endorphin appeared to be a result of a mild hypothermia caused by the neuropeptide. beta-Endorphin, however, did not influence the disease in nude (nu/nu) mice even though their core temperatures were reduced to an extent similar to that of BALB/c (+/+) mice, implicating the involvement of T lymphocytes in the alteration of the course of infection in normal mice.

Beta-endorphin suppresses rat plaque-forming cell response by a non-opioid mechanism

The opioid peptide beta h-endorphin 1-31 inhibited the plaque-forming cell (PFC) response to sheep red blood cells when rat splenocytes, immunized in vivo, were cultured in vitro with the peptide. The opioid antagonist naloxone failed to reverse the beta h-endorphin 1-31 suppression of the PFC response. Peptide fragments of beta h-endorphin 1-31, other opioid peptides, and alkaloids had no effect on the response. These data indicate that beta h-endorphin 1-31 suppresses antibody production or secretion by a specific, non-opioid receptor on the rat splenocytes.

Modulation of mitogen-induced spleen cell proliferation and the antibody-forming cell response by beta-endorphin in vivo

Experiments were conducted which compared the in vivo effects of beta-endorphin (BEP), gamma-endorphin (gamma EP), methionine-enkephalin (Met-ENK), and acetylated BEP(1-27) on the in vitro proliferative response of rat spleen cells to concanavalin A (ConA). In addition, the influence of BEP administration on the primary and secondary antibody-forming cell (AFC) response to the soluble antigen keyhole-limpet hemocyanin (KLH) was examined. Intravenous administration of BEP enhanced the spleen cell proliferative response to ConA assessed 3 hr after a single bolus infusion. Conversely, infusion with AcBEP(1-27) suppressed the proliferative response, whereas no effects of intravenous gamma EP or Met-ENK treatment were observed. The enhancing effect of BEP administration was not detectable 24 hr after a single infusion, but could be maintained over a 44 hr period by multiple infusions. The primary AFC response to KLH was suppressed by a dose of 1 nmole BEP only. On the other hand, the secondary IgG AFC response to KLH was enhanced by 10 pmoles BEP, while the IgM and IgA AFC responses remained unaltered by BEP treatment. The anamnestic in vitro proliferative response of spleen cells cultured with KLH was not altered if BEP was administered at the time of secondary KLH immunization. These results extend previous observations of BEP-induced modulation of in vitro immune function by demonstrating that opioid and nonopioid forms of BEP administered in vivo alter the capacity of spleen cells to proliferate and develop antibody responses to antigen.

Effect of neuropeptides and monoamines on lymphocyte activation

Neuropeptides and monoamines have been found in tissues where immune reactions are initiated such as the skin, gut, and respiratory tract, and in these tissues neuropeptides and monoamines might be involved in the regulation of lymphocyte activation. Studies both in in vitro and in vivo showing that various neuropeptides and monoamines may influence reactions such as T lymphocyte proliferation, B lymphocyte proliferation, and antibody synthesis, lymphocyte migration, and cytotoxicity will be reviewed.

Regulation of human natural cytotoxicity by enkephalins and selective opiate agonists

This study reports a bidirectional effect of the enkephalins and selective opiate receptor agonists on human natural killer (NK) cell activity. Peripheral blood mononuclear cells (PBMC) were obtained from healthy donors and enriched for T lymphocytes and large granular lymphocytes (LGL) by passage over nylon wool columns. Nylon wool nonadherent cell populations were preincubated for 18 h in the presence of fetal bovine serum with and without methionine-enkephalin, leucine-enkephalin, dynorphin (fragment 1-13), [D-Ser2]-leucine-enkephalin-Thr (DSLET), and [D-Ala2,N Me-Phe4, Gly-ol5]-enkephalin (DAGO). NK activity was measured by a standard 51Cr release assay with radiolabeled K562 cells. The cytolytic capacity of low NK responder populations was enhanced by the endogenous opioids while the NK activity of high responder populations was suppressed. These results suggest an immunoregulatory action of opioid peptides on NK activity. This possibility was confirmed using a serum-free system in conjunction with recombinant interferon-alpha. In addition, the classic opioid receptor antagonist naloxone displayed both antagonist and direct immunomodulatory properties, which may indicate the presence of lymphocyte derived opioid peptides in the culture system.

Opioid peptides modulate immune functions. A review

In the past few years it has become evident that neuropeptides may be direct mediators in the modulation of the immune response and the unspecific defense by the brain. Lymphocytes have been thought to have opioid receptors and to respond to opioids with an increase in blastogenesis, cytotoxicity and factor release. Lymphocytes are said to release various neuropeptides. Furthermore, there are some unexplained effects of morphine on the immune system and of the immune system on morphine withdrawal. The purpose of this paper is to review what has been previously published in this field. The well established modulation of phagocyte functions by opioids will only be scanned.

Modulation of the autologous mixed lymphocyte reaction by beta-endorphin

The effect of the opiate peptide, beta-endorphin (beta-END), on the autologous and allogeneic mixed lymphocyte reaction was examined. Physiologic concentrations of beta-END augmented proliferation of the autologous mixed lymphocyte reaction (AMLR) but the allogeneic MLR was not altered. Alpha-endorphin (alpha-END) was ineffective. Pre-incubation of the stimulator subset (i.e., B cells and macrophages) with 10(-8) M beta-END followed by addition to AMLR culture without additional opiate peptide did not produce augmentation. The beta-END-induced augmentation of the AMLR was partially inhibited by the opiate antagonist naloxone. beta-END augmentation was not due to increased secretion of interleukin-2. When prostaglandin E2 (PGE2) was added to AMLR cultures wherein the stimulator cell fraction was vigorously depleted of adherent cells, suppression was observed which could be reversed by the addition of beta-END (10(-8) M). The potential mechanisms producing the increased proliferative response during the AMLR are discussed.

Beta-endorphin modulation of mitogen-stimulated calcium uptake by rat thymocytes

Lymphocytes stimulated by mitogens or antigens exhibit an enhanced calcium uptake early in the proliferation or activation response. Modulation of this calcium uptake results in alterations of proliferation and immunocompetence. beta-endorphin and other opioids affect several parameters of lymphocyte competence. Limited data are available concerning the mechanism(s) of these effects. This study examines whether a possible opioid mechanism is the modification of the early calcium influx into stimulated lymphocytes. The time course of both concanavalin A (Con A) and phytohemagglutinin (PHA)-stimulated 45Ca2+ uptake into thymocytes was characterized to determine the optimal time for testing the effects of opioids. beta-Endorphin 1-31 significantly enhanced Con A-stimulated 45Ca2+ uptake into rat thymocytes. This peptide had no significant effect on PHA-stimulated 45Ca2+ uptake or on basal thymocyte 45Ca2+ flux. The beta h-endorphin stimulatory effect was titratable in the range of 0.1 nM to 10 microM. Naloxone did not reverse the enhancement. Met-enkephalinamide and other opioid agonists did not duplicate the stimulatory effect. Thus, the beta h-endorphin 1-31 enhancement of Con A-stimulated 45Ca2+ uptake by rat thymocytes does not operate via classical opioid receptor mechanisms. beta h-endorphin 1-31 appears to be acting on a subset of T cells that are responsive to Con A but not to PHA.

Endorphinergic modulation of immune function: potent action of the dipeptide glycyl-L-glutamine

Glycyl-L-glutamine (GLG), the carboxy terminal dipeptide of B-endorphin, inhibits brainstem neuronal activity. It also occurs along with B-endorphin in pituitary secretory vesicles suggesting a neurosecretory role for this dipeptide. We have evaluated potential immunoregulatory actions of this compound using the Phytohemaglutinin (PHA) blastogenesis and the concanavalin A (ConA) suppressor cell induction assays. GLG in low doses (10(-12) M) enhanced the response of human lymphocytes to PHA induced blastogenesis, however; with higher doses of the dipeptide (10(-7) M) immunosuppression was consistently observed. In the suppressor cell induction assay, when GLG was used together with ConA, we observed a dose-dependent inhibition of suppressor activity. These results clearly indicate that GLG produces a dose dependent bidirectional modulation of at least two indicies of immune function, and confirm the presence of a second pituitary peptide with the potential for potent immunomodulatory action.

Modulation of human concanavalin A-induced lymphocyte proliferative response by physiological concentrations of beta-endorphin

The effects of physiological concentrations of beta-endorphin on the proliferative response to concanavalin A of human peripheral blood mononuclear cells from a large series of healthy donors are reported. These effects are also compared with those obtained employing beta-endorphin and phytohemagglutinin under the same experimental conditions. The donors (32), aged between 20 and 48 years, chosen among military personnel of the Italian Air Force, underwent clinical and laboratory investigations to exclude any detectable disturbance in their psychophysical fitness. Our results show that beta-endorphin is not mitogenic per se and is unable to modify the response of mononuclear cells to phytohemagglutinin irrespective of the concentration of opioid or mitogen used. beta-Endorphin is also unable to alter the PBMC response to low concentrations of concanavalin A, but significantly increases such a response when higher concentrations of concanavalin A and concentrations of beta-endorphin similar to those found in human plasma under physiological conditions are used. The effect is not reverted by naloxone, the specific opiate antagonist. When the activity of beta-endorphin on the mononuclear cell response to concanavalin A is examined at the single donor level, it is noted that some of the donors fail to show the opioid-dependent increase. The baseline levels of the response to concanavalin A of such subjects, compared to those of the donors whose response is augmented by the opioid, are significantly higher, thus demonstrating that beta-endorphin can selectively modulate concanavalin A-induced mitogenesis with a behavior depending on the individual characteristics of the donor's response. The process involves non-opioid cell receptors.

The influence of nerve growth factor on the in vitro proliferative response of rat spleen lymphocytes

Splenic lymphocytes and accessory cells express receptors for nerve growth factor (NGF), a well-characterized neurotropic peptide that influences the development and survival of neuronal elements in the central and peripheral nervous systems. In the present study, we report that when rat splenic mononuclear cells (MC) are incubated in the presence of NGF, a dose-dependent increase in DNA synthesis occurs during 96-120 hours of culture as measured by 3H thymidine (3H-Thd) uptake. The minimal molar concentration of NGF at which the increased proliferative response of the cells (3.7 nM) is seen corresponded to the equilibrium disassociation binding constant of the MC (Kd = 2.5 nM), suggesting that the response was a consequence of receptor-ligand interaction. In addition, NGF was able to potentiate the lymphoproliferative response to several T-cell and B-cell mitogens. Significantly increased 3H-Thd uptake by NGF-stimulated cells was noted for concanavalin A (Con A), phytohemagglutinin (PHA), and lipopolysaccharide (LPS), particularly at suboptimal dosages of mitogen. Thus it appears that the NGF receptors on rat splenic MC are physiologically relevant and that NGF can modulate proliferation of T- and B- cells.

Effects of dynorphin on the PHA-induced lymphocyte proliferation in vitro

The effect of the opioid peptide dynorphin (DYN) on PHA-induced lymphocyte proliferation has been evaluated in the present study. A significant increase in PHA-induced lymphocyte activation was observed when DYN was added to cultures 48 hr after the mitogenic stimulation. This effect occurred at suboptimal (3.12 and 6.25 micrograms/ml) PHA concentrations and at DYN doses ranging from 10(-9) to 10(-12) M. Conversely, DYN did not affect the lymphocyte blastogenic process either when added before, or simultaneously or after intense PHA (12.5 micrograms/ml) stimulation. Naloxone preincubation did not modify the above described effects. Results suggest that DYN might play a role in neuroendocrine regulation of the lymphocyte blastogenic process.