The effects of prostaglandins on the proliferation of cultured human T lymphocytes

Post-resolution macrophages shape long-term tissue immunity and integrity in a mouse model of pneumococcal pneumonia

Resolving inflammation is thought to return the affected tissue back to homoeostasis but recent evidence supports a non-linear model of resolution involving a phase of prolonged immune activity. Here we show that within days following resolution of Streptococcus pneumoniae-triggered lung inflammation, there is an influx of antigen specific lymphocytes with a memory and tissue-resident phenotype as well as macrophages bearing alveolar or interstitial phenotype. The transcriptome of these macrophages shows enrichment of genes associated with prostaglandin biosynthesis and genes that drive T cell chemotaxis and differentiation. Therapeutic depletion of post-resolution macrophages, inhibition of prostaglandin E2 (PGE2) synthesis or treatment with an EP4 antagonist, MF498, reduce numbers of lung CD4+/CD44+/CD62L+ and CD4+/CD44+/CD62L-/CD27+ T cells as well as their expression of the α-integrin, CD103. The T cells fail to reappear and reactivate upon secondary challenge for up to six weeks following primary infection. Concomitantly, EP4 antagonism through MF498 causes accumulation of lung macrophages and marked tissue fibrosis. Our study thus shows that PGE2 signalling, predominantly via EP4, plays an important role during the second wave of immune activity following resolution of inflammation. This secondary immune activation drives local tissue-resident T cell development while limiting tissue injury.

Prostaglandin E2 and T cells: friends or foes?

Our understanding of the key players involved in the differential regulation of T-cell responses during inflammation, infection and auto-immunity is fundamental for designing efficient therapeutic strategies against immune diseases. With respect to this, the inhibitory role of the lipid mediator prostaglandin E₂ (PGE₂) in T-cell immunity has been documented since the 1970s. Studies that ensued investigating the underlying mechanisms substantiated the suppressive function of micromolar concentrations of PGE₂ in T-cell activation, proliferation, differentiation and migration. However, the past decade has seen a revolution in this perspective, since nanomolar concentrations of PGE₂ have been shown to potentiate Th1 and Th17 responses and aid in T-cell proliferation. The understanding of concentration-specific effects of PGE₂ in other cell types, the development of mice deficient in each subtype of the PGE₂ receptors (EP receptors) and the delineation of signalling pathways mediated by the EP receptors have enhanced our understanding of PGE₂ as an immune-stimulator. PGE₂ regulates a multitude of functions in T-cell activation and differentiation and these effects vary depending on the micro-environment of the cell, maturation and activation state of the cell, type of EP receptor involved, local concentration of PGE₂ and whether it is a homeostatic or inflammatory scenario. In this review, we compartmentalize the various aspects of this complex relationship of PGE₂ with T lymphocytes. Given the importance of this molecule in T-cell activation, we also address the possibility of using EP receptor antagonism as a potential therapeutic approach for some immune disorders.

Review of lithium effects on brain and blood

Clinicians have long used lithium to treat manic depression. They have also observed that lithium causes granulocytosis and lymphopenia while it enhances immunological activities of monocytes and lymphocytes. In fact, clinicians have long used lithium to treat granulocytopenia resulting from radiation and chemotherapy, to boost immunoglobulins after vaccination, and to enhance natural killer activity. Recent studies revealed a mechanism that ties together these disparate effects of lithium. Lithium acts through multiple pathways to inhibit glycogen synthetase kinase-3beta (GSK3 beta). This enzyme phosphorylates and inhibits nuclear factors that turn on cell growth and protection programs, including the nuclear factor of activated T cells (NFAT) and WNT/beta-catenin. In animals, lithium upregulates neurotrophins, including brain-derived neurotrophic factor (BDNF), nerve growth factor, neurotrophin-3 (NT3), as well as receptors to these growth factors in brain. Lithium also stimulates proliferation of stem cells, including bone marrow and neural stem cells in the subventricular zone, striatum, and forebrain. The stimulation of endogenous neural stem cells may explain why lithium increases brain cell density and volume in patients with bipolar disorders. Lithium also increases brain concentrations of the neuronal markers n-acetyl-aspartate and myoinositol. Lithium also remarkably protects neurons against glutamate, seizures, and apoptosis due to a wide variety of neurotoxins. The effective dose range for lithium is 0.6-1.0 mM in serum and >1.5 mM may be toxic. Serum lithium levels of 1.5-2.0 mM may have mild and reversible toxic effects on kidney, liver, heart, and glands. Serum levels of >2 mM may be associated with neurological symptoms, including cerebellar dysfunction. Prolonged lithium intoxication >2 mM can cause permanent brain damage. Lithium has low mutagenic and carcinogenic risk. Lithium is still the most effective therapy for depression. It "cures" a third of the patients with manic depression, improves the lives of about a third, and is ineffective in about a third. Recent studies suggest that some anticonvulsants (i.e., valproate, carbamapazine, and lamotrigene) may be useful in patients that do not respond to lithium. Lithium has been reported to be beneficial in animal models of brain injury, stroke, Alzheimer's, Huntington's, and Parkinson's diseases, amyotrophic lateral sclerosis (ALS), spinal cord injury, and other conditions. Clinical trials assessing the effects of lithium are under way. A recent clinical trial suggests that lithium stops the progression of ALS.

Plattenepithelkarzinome des Kopf-Hals-Bereichs

Biologic therapies able to induce or up-regulate anti-tumor immune responses could represent a complementary approach to improve the conventional treatment of squamous cell carcinomas of the head and neck (SCCHN). Patients with SCCHN are frequently immunocompromised due to the elimination and dysfunction of critical immune effector cells. Therefore, it might be necessary to restore these immune functions to allow for the generation of effective anti-tumor host responses. Simultaneously, to prevent tumor escape from immunological recognition and destruction, it might also be necessary to alter antigenic and immunogenic attributes of the malignant cells. The present overview summarizes general aspects, historical data, and recent advances in the field of immunotherapy of SCCHN, including non-specific immune stimulation, transfer of immunocompetent cells, gene therapy, use of monoclonal antibodies, and anti-cancer vaccines.

Targeting the immune system: novel therapeutic approaches in squamous cell carcinoma of the head and neck

Despite advances in surgery, radiotherapy, and chemotherapy, the overall survival rates for patients with squamous cell carcinoma of the head and neck (SCCHN) have not changed over the last decades. Clearly, novel therapeutic strategies are needed for this cancer, which is highly immunosuppressive. Therefore, biologic therapies able to induce and/or up-regulate antitumor immune responses could represent a complementary approach to conventional treatments. Because patients with SCCHN are frequently immunocompromised due to the elimination or dysfunction of critical effector cells of the immune system, it might be necessary to restore these immune functions to allow for the generation of more effective antitumor host responses. Simultaneously, to prevent tumor escape, it might be necessary to alter attributes of the malignant cells. The present review summarizes recent advances in the field of immunotherapy of SCCHN, including techniques of nonspecific immune stimulation, the use of monoclonal antibodies, advances in adoptive immunotherapy and genetic engineering, as well as anticancer vaccines. These biologic therapies, alone or in combination with conventional treatment, are likely to develop into useful future treatment options for patients with SCCHN.

Suppression of mitogen-induced lymphoproliferation by soluble IgG Fc receptors in retroplacental serum in normal human pregnancy

A competitive ELISA was used to quantify soluble IgG Fc receptors (FcR) in retroplacental serum (RPS) and peripheral serum (PS) from 10 women after uncomplicated full-term deliveries. The RPS contained significantly higher amounts of soluble FcR than did PS from the same individuals. RPS suppressed phytohaemagglutinin-stimulated lymphoproliferation as compared with PS, and a positive correlation (r = 0.66) was found between the degree of suppression and the difference in soluble FcR level between RPS and PS. Absorption of sera with Sepharose 4B coupled with heat-aggregated IgG strongly reduced the immunosuppressive activity, whereas absorption with Sepharose coupled with IgG F(ab')2 fragments did not. When IgG-binding material was eluted from Sepharose beads and added to cell cultures, the immunosuppressive activity was restored. The data indicate that soluble FcR at physiological levels have immunosuppressive properties. FcR-mediated immunosuppression may be of importance for maintenance of local immunosuppression during pregnancy.

Generation of leukotrienes and hydroxyeicosatetraenoic acids in peritoneal macrophages of tumor-bearing mice

To examine the potential role of lipoxygenase products in the pathophysiology observed after experimental tumor implantation, we examined the generation of leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs) in peritoneal macrophages. C57BL/6 mice were given subcutaneous inoculations of B16 melanoma cells, and peritoneal macrophages were isolated various days after the inoculation. Macrophages were incubated for 1 h at 37 degrees C in serum-free RPM11640 containing 10 microM calcium ionophore A23187, 10 microM exogenous arachidonic acid (AA), 5 mM cysteine hydrochloride and 1 mM reduced glutathione. LTs and HETEs were separately extracted, passed through Sep-Pak cartridges, then identified and quantitated with a HPLC system using UV absorbance. The B16 melanoma-cell-treated/untreated macrophages were found to produce substantial amounts of 15-HETE, 12-HETE and 5-HETE and LTC4 by enzymatic mechanisms. Thus, when determined under various conditions, the production of HETEs was dependent on substrate-concentration, incubation-time and cell-number. The production of LTC4 was dependent on incubation-time and cell number but not substrate-concentration, indicating utilization of endogenous AA stores. Of these products, 12-HETE and LTC4 showed a significant increase on the fourth day after the tumor cell inoculation and returned to the control level by the 11th day after the same treatment. These results suggest that in vivo tumor cell implantation may induce a transient increase of 12-HETE and LTC4 production in macrophages.

Indomethacin modulation of adriamycin-induced effects on multiple cytolytic effector functions

The anticancer agent, Adriamycin (ADM), in addition to being a potent cytotoxic drug has been shown to be an effective immunomodulator. This study was undertaken to determine whether ADM-induced changes in the production of prostaglandins (particularly PGE2) are involved in ADM-associated modifications of selected host defenses. Spleen cells from normal or ADM-treated (5 mg/kg; day -5) C57BL/6 mice were assessed for the following activities: fresh (day 0) and cultured natural killer (NK), cytotoxic T lymphocyte, lymphokine-activated killer (LAK), Fc-dependent phagocytosis and tumoricidal macrophage. All activities were assessed with and without the addition of indomethacin, an inhibitor of the first step of the cyclo-oxygenase pathway of prostaglandin synthesis. Depending on culture conditions, the cytotoxic T lymphocyte and splenic tumoricidal macrophage activities were either unaffected or were augmented by ADM treatment of the spleen donor mice or by addition of indomethacin to the culture, and these effects were apparently independent of one another. In contrast, ADM treatment generally resulted in reduced NK and LAK activities relative to control and elevated Fc-dependent phagocytosis. The addition of indomethacin to the culture effectively reversed these effects. Furthermore, spleen cells from ADM-treated mice were found to produce twice the amount of PGE2 in culture compared to cells from untreated mice. Finally, the direct addition of PGE2 to NK cultures resulted in a dose-dependent inhibition of NK activity and the dose required was comparable to the amount of PGE2 produced by cultured spleen cells from ADM-treated mice. Taken together, these results indicate that at least some of the immunomodulatory effects of ADM are an indirect result of ADM-induced changes in PGE2 production.

Detection of immunoregulatory factors in retroplacental serum in human pregnancy

Retroplacental serum (RPS) obtained from pregnant women at term deliveries was studied for regulatory effects on T-lymphocyte proliferation and for pregnancy-associated substances and compared with peripheral serum (PS) of the same donor. Proliferative response to phytohemagglutinin and alloantigens in RPS was lower than that in PS. RPS contained higher levels of human placental lactogen, progesterone, estradiol, and prostaglandin E2 than of PS. However, there were no differences in concentrations of pregnancy-associated alpha 2-glycoprotein, pregnancy-specific beta 1-glycoprotein, prostaglandin F2 alpha, alpha-fetoprotein, human chorionic gonadotropin, cortisol, carcinoembryonic antigen, and immunoglobulins between RPS and PS. The amounts of human placental lactogen, progesterone, or prostaglandin E2 seen in RPS did not inhibit T-cell proliferation. Mixtures of various doses of these three substances were still not inhibitory. Thus, the suppressive activity of RPS could not be explained by these pregnancy-associated substances, but a possible involvement of unknown immunoregulatory factors at fetomaternal interface might be suggested.

Sequential bacteriological observations in relation to cell-mediated and humoral antibody responses of cattle infected with Mycobacterium paratuberculosis and maintained on normal or high iron intake

Twenty calves were orally infected with Mycobacterium paratuberculosis before weaning. Ten of these plus 4 non-infected controls were maintained on elevated dietary iron intake from 6 to 33 months of age. During this time, in which the majority of animals were bred, the influence of increased dietary iron upon tests of cellular and humoral immune responsiveness to antigens of the organism were monitored. Results were examined in relation to the organism's capacity to multiply and infect up to 7 portions of the intestinal tract. No significant differences were detected in the degree of intestinal disease or pattern of faecal excretion of M. paratuberculosis in iron supplemented and non-supplemented cattle. Cutaneous delayed-type hypersensitivity (DTH) to johnin PPD developed at 1 month and in-vitro lymphocyte and immunostimulatory activity (LS) to this antigen at 2 months after infection. LS indices were significantly reduced in magnitude in iron-supplemented cattle (p less than 0.01). Most ELISA antibody responses were positive 10 to 17 months after infection and preceded the fewer number of CF responses by several months. Neither of the antibody tests was affected by elevated iron intake. Generally, complete or partial resistance to paratuberculosis was associated with sustained positive monthly LS tests (index greater than or equal to 2.0), whereas antibody levels tended to be sustained only in the more severely affected cattle. Although neither test system was affected by pregnancy the ELISA failed to detect a significant proportion of cattle chronically shedding M. paratuberculosis in faeces.

Pharmacological inhibition of interleukin-1 activity on T cells by hydrocortisone, cyclosporine, prostaglandins, and cyclic nucleotides

The effects of a panel of hormones and pharmacological agents on the activation of T cells by a combination of interleukin-1 and phytohemagglutinin (IL-1/PHA) was studied. Pharmacological effects on various stages of IL-1/PHA-induced interleukin-2 (IL-2) production by the cloned murine thymoma cell line LBRM-33-1A5.7 were dissected using a multi-step assay procedure. A 4-h lag phase in the kinetics of IL-2 production allowed the operational definition of an early, IL-1-dependent programming stage, followed by an IL-2-production stage of the assay. A cell-washing procedure between these stages was introduced in order to distinguish IL-1 receptor antagonists from functional IL-1/PHA antagonists. Hydrocortisone and cyclosporine were potent inhibitors (active in the nM range) of both stages of IL-2 production, suggesting that neither is an IL-1 receptor antagonist. The cyclic adenosine monophosphate (cAMP)-elevating agents prostaglandin E2, dibutyryl cAMP, and theophylline inhibited IL-2 production during the early, IL-1-dependent programming stage. By contrast, prostaglandin F2 alpha and dibutyryl cyclic guanosine monophosphate did not appreciably inhibit IL-1/PHA activity. These results are discussed in relationship to the effects of these test agents in thymocyte IL-1 assays or mitogenesis assays and the implications toward understanding the mechanisms underlying IL-1/PHA activation of T cells.

In vitro modulation of macrophage functions by 1,1-dimethylhydrazine (UDMH): Possible mechanism for UDMH-induced immuno-enhancement

The in vitro effects of 1,1-dimethylhydrazine (UDMH) on prostaglandin E(2) (PGE(2)) synthesis, chemiluminescence, phagocytosis, microbicidal activity and chemotaxis in murine enriched-macrophage populations were evaluated. PGE(2) synthesis by resident peritoneal macrophages and chemiluminescence by activated macrophages were markedly suppressed in the presence of UDMH; phagocytosis and microbicidal activity were slightly to moderately suppressed, and chemotaxis was not affected. Two of these functions (PGE(2) synthesis and chemiluminescence) reflect macrophage immunoregulatory properties, and the UDMH-induced abrogation of these functions may be related to the previously reported immuno-enhancing effects of UDMH.

In vitro effects of thymosin and lithium on lymphoproliferative responses of normal donors and HIV seropositive male homosexuals with AIDS-related complex

The in vitro effects of thymosin fraction 5 (TF5) and lithium chloride (LiCl) on the ability of peripheral blood mononuclear cells (PBMC) obtained from 37 normal male donors and 33 male patients with AIDS-related complex (ARC) to respond to alloantigenic stimulation (mixed leukocyte reaction, MLR) and to produce interleukin 2 (IL-2) in response to mitogens were studied. TF5 significantly increased MLR responses in normal donors (P less than 0.01) and in a group of 33 ARC patients with depressed cellular immunity (P less than 0.05). Similar effects were observed when LiCl was added to the MLR assays in both the normal and the ARC patient groups. Furthermore, TF5 and LiCl exhibited additive immunoenhancing properties. In 10 normal donors TF5 enhanced phytohemaggutinin (PHA)-induced IL-2 production as well as IL-2 production in response to pokeweed mitogen (PWM) (P less than 0.02). TF5-mediated enhancement of IL-2 production by PBMC obtained from ARC patients was observed in response to both mitogens, i.e., PHA and PWM. Additionally, LiCl increased PHA-induced IL-2 production in both normal subjects and ARC patients. LiCl and TF5 together had an additive effect in the enhancement of IL-2 production in both groups of subjects. Our data extend previous observations regarding the immunoregulatory activities of TF5 and LiCl and provide evidence that PBMC obtained from ARC patients have the potential to respond in vitro to these agents. The significance of these findings is discussed.

A study on plasma prostaglandin E2 levels in hepatitis B carriers and patients with chronic active hepatitis

Prostaglandin E2 (PGE2), one of the major prostaglandins synthesized in human monocyte and macrophage, is able to modulate T lymphocyte reactivity, such as lymphokine secretion and cytotoxicity. Some immunologic abnormalities such as alteration in the synthesis of PGE2 by monocyte and macrophage or in the response of T lymphocytes to PGE2 can be found in clinical disease.

We measured the plasma PGE2 level in the control group and patients with chronic liver disease.

The results were obtained as follows. The mean plasma PGE2 level was 2.65 ± 0.69 pg/ml in the control group. The mean plasma PGE2 level was 9.07 ± 5.89 pg/ml in 15 patients with chronic active hepatitis and was significantly higher than that of the control group (p<0.01). The plasma mean PGE2 level was 4.65 ± 1.59 pg/ml in 8 patients in the healing stage or stable stage of chronic hepatitis and was tend to decrease. However, this decrease is significantly different from that of the control group. The plasma PGE2 level was 3.5 ± 0.92 pg/ml in 4 hepatitis B carriers and was not significantly different from that of the control group (p<0.05).

This results suggest that plasma PGE2 can be used for the measurement of cell-mediated immunity and follow-up study in patients with chronic active hepatitis and hepatitis B carriers.

The combined effect of prostaglandin E2 and interleukin 1 on interleukin 2 production and lymphocyte proliferation

In this study the combined effect of prostaglandin E2 (PGE2) and interleukin-1 (IL-1) on the proliferation of concanavalin A (Con A) stimulated mouse spleen lymphocytes was studied. IL-1 in concentrations ranging from 0.5 to 5.0 U/ml consistently and significantly enhanced Con A activity. However, to be effective, IL-1 needed to be added at the time of initiation of the culture. If added 24 h later, IL-1 failed to enhance the proliferative response. PGE2 at concentrations ranging from 0.1 to 5.0 ng/ml effectively inhibited or antagonized this enhancing effect of IL-1, with the majority of this IL-1 augmentation abrogated by 5.0 ng/ml PGE2. Unlike IL-1, PGE2 was as effective if added 24 h after initiation of the culture as if added simultaneously with IL-1. PGE2 was also found to markedly suppress the enhanced production of IL-2 resulting from the addition of IL-1 to Con A stimulated lymphocytes, however, the amount of IL-2 produced in the cultures containing both IL-1 and PGE2 was always greater than that produced in the cultures which contained only PGE2. This finding indicates that IL-1 could partially reverse or antagonize the suppressive effect of PGE2 on IL-2 production. In addition, PGE2 at concentrations of 1.0 and 5.0 ng/ml was also found to inhibit the proliferation of IL-2 stimulated cultured T lymphocytes, but by only about 15-20%. The addition of IL-1 to these cultured T cells neither altered the response of the culture T cells to IL-2 nor altered the sensitivity of these cells to PGE2.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppressive effect of thymosin fraction 5 on proliferation of cultured human T lymphocytes

The effects of thymosin fraction 5 (F5), an extract of bovine thymus containing multiple polypeptides, on the proliferation of cultured T cells (CTC), a continuously proliferating subpopulation of peripheral blood T lymphocytes, stimulated by either phytohemagglutinin (PHA) or delectinated interleukin 2 (IL-2) were studied. Addition of F5 to cultures significantly and consistently inhibited CTC responsiveness to PHA, with the degree of inhibition being greater using a suboptimal concentration of mitogen. F5 did not significantly or consistently inhibit CTC proliferation induced by IL-2. These studies suggest that the suppressive effect of F5 may be primarily mediated by decreased IL-2 production instead of effects on IL-2 activity or efficiency in stimulating CTC proliferation. Since prostaglandins inhibit the proliferation of CTC in response to PHA or IL-2 (R.D. Maca (1983) Immunopharmacology 6:267), studies were undertaken to determine if the observed inhibition was mediated by effects of F5 on prostaglandin E2 (PGE2). The inhibitory effect of F5 on PHA responsiveness of CTC was not affected by the addition of indomethacin indicating that suppression by F5 is not mediated by stimulating the production or release of cyclooxygenase-derived prostaglandins, such as PGE2. Furthermore, PGE2 could not be detected in supernatants of F5-treated CTC stimulated by PHA. When PGE2 was added to F5-treated CTC cultures, the PHA response was inhibited indicating that the suppressive effects of F5 and PGE2 were additive and that F5 did not modulate the sensitivity of CTC to PGE2.(ABSTRACT TRUNCATED AT 250 WORDS)

Lymphocyte activation by the Fc region of immunoglobulins

The Fc region of Ig is required for numerous biological effector functions which include: opsonization, anaphylaxis, C fixation, catabolism of the Ig molecule, FcR binding, and immune regulation. To this latter point, the cellular and subcellular events involved in immune regulation by IC and Fc fragments of Ig have been the focus of numerous investigations. Characterization of cyanogen bromide cleavage fragments from a human IgG1 myeloma protein indicates that one biologically-active site is found in residues 335-357 of the CH3 domain of the molecule. Synthesis of the biologically-active region resulted in a peptide, termed p23, which stimulates mouse and human B cells to secrete polyclonal Ig and activates AA metabolic pathways. In contrast to these findings, p23 is unable to induce B cell proliferation or IL-1 secretion from macrophages. Analysis of data obtained with overlapping peptides, based on p23, suggests that the minimal active sequence needed for B cell differentiation is leu-pro-pro-ser-arg (residues 351-355). In contrast, only p23 or p23 minus the carboxyterminal glu356 and glu357 were able to induce PGE release. Release of biologically-active peptides derived from the Fc region of Ig into the cellular microenvironment may form the nucleus of a nonspecific in vivo immunoregulatory network. The specificity of peptide regulatory activities could reside in their effectiveness at high concentrations in the cellular microenvironment. The interaction of Fc region peptides with receptors on B cells, T cells, and macrophages/monocytes could result in a dynamic control of immune reactivity.

The production of prostaglandin and the regulation of cell division in neonate rat primary mixed glial cultures

The production of prostaglandins has been studied in neonate rat primary mixed glial cultures. A correlation was found between inhibition of [3H]thymidine incorporation in the cultures and production of prostaglandin, which was stimulated by the addition of supernatant from Con A-activated rat splenocytes. Inhibition of prostaglandin synthesis in the cultures by indomethacin results in a striking increase in incorporation of [3H]thymidine into the cultures, an effect which was reversed by the addition of exogenous PGE2, but not PGF2 alpha. PGE was the principal prostaglandin detected, with both macrophages/microglia and astrocytes contributing to the output. A possible role for prostaglandins in the modulation of inflammatory responses in the central nervous system is discussed.

Stimulation of arachidonic acid release and eicosanoid biosynthesis in an interleukin 2-dependent T cell line

Previous studies have provided pharmacologic evidence that T lymphocyte function may be regulated in part by the intracellular production of various arachidonic acid (AA) metabolites in response to cellular stimulation. However, the specific AA metabolic capabilities of homogeneous T cell populations have not been clearly defined. In the present studies, we have employed an accessory cell-free T cell line, HT-2, as a model system for the examination of stimulus-induced eicosanoid biosynthesis in T lymphocytes. HT-2 cells were biosynthetically labeled with [3H]-AA and challenged briefly with various agents that stimulate the hydrolytic release of AA from cellular phospholipids. The bee venom peptide melittin stimulated a profound AA release response in the cells and the concomitant synthesis of both cyclooxygenase (PGF2 alpha, PGE2 and PGD2) and lipoxygenase (5-,12-,15-HETE and possibly 5-,12-diHETE) metabolites of AA. The formation of PGs was blocked by 5 microM indomethacin, demonstrating that this cell line contains cyclooxygenase activity functionally similar to that described in macrophages and other cell types. The high activity of melittin in this system was shown to result largely from a synergy between the peptide itself and a persistent bee venom phospholipase A2 contaminant. However, experiments with melittin freed of detectable phospholipase A2 activity by heating, and with synthetic homopolymers of (L)-lysine and (L)-arginine demonstrated that HT-2 cells contain sufficient endogenous, stimulus-responsive phospholipase A2 to provide both the cyclooxygenase and lipoxygenase pathways of AA metabolism ith substrate. In contrast, Ca++ ionophores, which are known to stimulate AA release and metabolism in certain cell types, stimulated only AA release but no detectable eicosanoid biosynthesis in HT-2 cells. Experiments with exogenous bacterial phospholipase C suggested that this cell line can also generate free AA for eicosanoid biosynthesis from membrane-derived 1,2-diacylglycerol. These results indicate that multiple intracellular pathways of AA metabolism are present HT-2 cells, and that the stimulus-induced release of AA and the production of eicosanoid second messengers may result from activation of either phospholipase A2 or phospholipase C.

Mechanism of action of thymosin. II. Effects of aspirin and thymosin on enhancement of IL-2 production

Recent studies have shown that thymosin fraction 5 (TF5) enhances production of interleukin-2 (IL-2) by phytohemagglutinin (PHA)-stimulated normal human peripheral blood mononuclear leukocytes (PBL). In this study we sought to determine whether this effect of TF5 might be mediated via the cyclooxygenase or lipoxygenase pathways. Our studies demonstrate that aspirin, an inhibitor of the cyclooxygenase pathway, given in vivo, or added to cultures in vitro, results in two-fold increased IL-2 production by PHA-stimulated PBL. This increase is comparable to that seen when PBL are cultured in vitro with TF5. When aspirin and TF5 are added simultaneously to PBL in the presence of PHA, an additive response is seen. An inhibitor of the lipoxygenase pathway, 15-hydroxyeicosatetraenoic acid, did not significantly change IL-2 production by PBL or influence the enhancement by TF5. Augmentation of IL-2 production by aspirin and/or TF5 was prevented by monocyte depletion of the PBL population. These results are interpreted as demonstrating (a) that TF5 and aspirin augment, by distinct mechanisms, IL-2 production by normal human PBL, (b) that the effects of both of these agents are mediated directly or indirectly via a monocyte population and (c) that aspirin, in addition to its analgesic and anti-inflammatory properties, may act as a modulator of immunological responsiveness, either alone or in combination with other biological response modifiers such as thymosin.