Human lymphocytic metabolism. Effects of cyclic and noncyclic nucleotides on stimulation by phytohemagglutinin

Prostaglandin E2 in the Tumor Microenvironment, a Convoluted Affair Mediated by EP Receptors 2 and 4

The involvement of the prostaglandin E2 (PGE2) system in cancer progression has long been recognized. PGE2 functions as an autocrine and paracrine signaling molecule with pleiotropic effects in the human body. High levels of intratumoral PGE2 and overexpression of the key metabolic enzymes of PGE2 have been observed and suggested to contribute to tumor progression. This has been claimed for different types of solid tumors, including, but not limited to, lung, breast, and colon cancer. PGE2 has direct effects on tumor cells and angiogenesis that are known to promote tumor development. However, one of the main mechanisms behind PGE2 driving cancerogenesis is currently thought to be anchored in suppressed antitumor immunity, thus providing possible therapeutic targets to be used in cancer immunotherapies. EP2 and EP4, two receptors for PGE2, are emerging as being the most relevant for this purpose. This review aims to summarize the known roles of PGE2 in the immune system and its functions within the tumor microenvironment. SIGNIFICANCE STATEMENT: Prostaglandin E2 (PGE2) has long been known to be a signaling molecule in cancer. Its presence in tumors has been repeatedly associated with disease progression. Elucidation of its effects on immunological components of the tumor microenvironment has highlighted the potential of PGE2 receptor antagonists in cancer treatment, particularly in combination with immune checkpoint inhibitor therapeutics. Adjuvant treatment could increase the response rates and the efficacy of immune-based therapies.

Regulatory role of vitamin E in the immune system and inflammation

Vitamin E, a potent lipid-soluble antioxidant, found in higher concentration in immune cells compared to other cells in blood, is one of the most effective nutrients known to modulate immune function. Vitamin E deficiency has been demonstrated to impair normal functions of the immune system in animals and humans, which can be corrected by vitamin E repletion. Although deficiency is rare, vitamin E supplementation above current dietary recommendations has been shown to enhance the function of the immune system and reduce risk of infection, particularly in older individuals. The mechanisms responsible for the effect of vitamin E on the immune system and inflammation have been explored in cell-based, pre-clinical and clinical intervention studies. Vitamin E modulates T cell function through directly impacting T cell membrane integrity, signal transduction, and cell division, and also indirectly by affecting inflammatory mediators generated from other immune cells. Modulation of immune function by vitamin E has clinical relevance as it affects host susceptibility to infectious diseases such as respiratory infections, in addition to allergic diseases such as asthma. Studies examining the role of vitamin E in the immune system have typically focused on α-tocopherol; however, emerging evidence suggests that other forms of vitamin E, including other tocopherols as well as tocotrienols, may also have potent immunomodulatory functions. Future research should continue to identify and confirm the optimal doses for individuals at different life stage, health condition, nutritional status, and genetic heterogeneity. Future research should also characterize the effects of non-α-alpha-tocopherol vitamin E on immune cell function as well as their potential clinical application. © 2018 IUBMB Life, 71(4):487-494, 2019.

Nutritional Modulation of Immune Function: Analysis of Evidence, Mechanisms, and Clinical Relevance

It is well-established that the nutritional deficiency or inadequacy can impair immune functions. Growing evidence suggests that for certain nutrients increased intake above currently recommended levels may help optimize immune functions including improving defense function and thus resistance to infection, while maintaining tolerance. This review will examine the data representing the research on prominent intervention agents n-3 polyunsaturated fatty acids (PUFA), micronutrients (zinc, vitamins D and E), and functional foods including probiotics and tea components for their immunological effects, working mechanisms, and clinical relevance. Many of these nutritive and non-nutritive food components are related in their functions to maintain or improve immune function including inhibition of pro-inflammatory mediators, promotion of anti-inflammatory functions, modulation of cell-mediated immunity, alteration of antigen-presenting cell functions, and communication between the innate and adaptive immune systems. Both animal and human studies present promising findings suggesting a clinical benefit of vitamin D, n-3 PUFA, and green tea catechin EGCG in autoimmune and inflammatory disorders, and vitamin D, vitamin E, zinc, and probiotics in reduction of infection. However, many studies report divergent and discrepant results/conclusions due to various factors. Chief among them, and thus call for attention, includes more standardized trial designs, better characterized populations, greater consideration for the intervention doses used, and more meaningful outcome measurements chosen.

Autonomic nervous system and immune system interactions

The present review assesses the current state of literature defining integrative autonomic-immune physiological processing, focusing on studies that have employed electrophysiological, pharmacological, molecular biological, and central nervous system experimental approaches. Central autonomic neural networks are informed of peripheral immune status via numerous communicating pathways, including neural and non-neural. Cytokines and other immune factors affect the level of activity and responsivity of discharges in sympathetic and parasympathetic nerves innervating diverse targets. Multiple levels of the neuraxis contribute to cytokine-induced changes in efferent parasympathetic and sympathetic nerve outflows, leading to modulation of peripheral immune responses. The functionality of local sympathoimmune interactions depends on the microenvironment created by diverse signaling mechanisms involving integration between sympathetic nervous system neurotransmitters and neuromodulators; specific adrenergic receptors; and the presence or absence of immune cells, cytokines, and bacteria. Functional mechanisms contributing to the cholinergic anti-inflammatory pathway likely involve novel cholinergic-adrenergic interactions at peripheral sites, including autonomic ganglion and lymphoid targets. Immune cells express adrenergic and nicotinic receptors. Neurotransmitters released by sympathetic and parasympathetic nerve endings bind to their respective receptors located on the surface of immune cells and initiate immune-modulatory responses. Both sympathetic and parasympathetic arms of the autonomic nervous system are instrumental in orchestrating neuroimmune processes, although additional studies are required to understand dynamic and complex adrenergic-cholinergic interactions. Further understanding of regulatory mechanisms linking the sympathetic nervous, parasympathetic nervous, and immune systems is critical for understanding relationships between chronic disease development and immune-associated changes in autonomic nervous system function.

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.

Sympathetic modulation of immunity: relevance to disease

Optimal host defense against pathogens requires cross-talk between the nervous and immune systems. This paper reviews sympathetic-immune interaction, one major communication pathway, and its importance for health and disease. Sympathetic innervation of primary and secondary immune organs is described, as well as evidence for neurotransmission with cells of the immune system as targets. Most research thus far has focused on neural-immune modulation in secondary lymphoid organs, has revealed complex sympathetic modulation resulting in both potentiation and inhibition of immune functions. SNS-immune interaction may enhance immune readiness during disease- or injury-induced 'fight' responses. Research also indicate that dysregulation of the SNS can significantly affect the progression of immune-mediated diseases. However, a better understanding of neural-immune interactions is needed to develop strategies for treatment of immune-mediated diseases that are designed to return homeostasis and restore normal functioning neural-immune networks.

Anti-inflammatory drugs in the 21st century

Historically, anti-inflammatory drugs had their origins in the serendipitous discovery of certain plants and their extracts being applied for the relief of pain, fever and inflammation. When salicylates were discovered in the mid-19th century to be the active components of Willow Spp., this enabled these compounds to be synthesized and from this, acetyl-salicylic acid or Aspirin was developed. Likewise, the chemical advances of the 19th-20th centuries lead to development of the non-steroidal anti-inflammatory drugs (NSAIDs), most of which were initially organic acids, but later non-acidic compounds were discovered. There were two periods of NSAID drug discovery post-World War 2, the period up to the 1970's which was the pre-prostaglandin period and thereafter up to the latter part of the last century in which their effects on prostaglandin production formed part of the screening in the drug-discovery process. Those drugs developed up to the 1980-late 90's were largely discovered empirically following screening for anti-inflammatory, analgesic and antipyretic activities in laboratory animal models. Some were successfully developed that showed low incidence of gastro-intestinal (GI) side effects (the principal adverse reaction seen with NSAIDs) than seen with their predecessors (e.g. aspirin, indomethacin, phenylbutazone); the GI reactions being detected and screened out in animal assays. In the 1990's an important discovery was made from elegant molecular and cellular biological studies that there are two cyclo-oxygenase (COX) enzyme systems controlling the production of prostanoids [prostaglandins (PGs) and thromboxane (TxA2)]; COX-1 that produces PGs and TxA2 that regulate gastrointestinal, renal, vascular and other physiological functions, and COX-2 that regulates production of PGs involved in inflammation, pain and fever. The stage was set in the 1990's for the discovery and development of drugs to selectively control COX-2 and spare the COX-1 that is central to physiological processes whose inhibition was considered a major factor in development of adverse reactions, including those in the GI tract. At the turn of this century, there was enormous commercial development following the introduction of two new highly selective COX-2 inhibitors, known as coxibs (celecoxib and rofecoxib) which were claimed to have low GI side effects. While found to have fulfilled these aims in part, an alarming turn of events took place in the late 2004 period when rofecoxib was withdrawn worldwide because of serious cardiovascular events and other coxibs were subsequently suspected to have this adverse reaction, although to a varying degree. Major efforts are currently underway to discover why cardiovascular reactions took place with coxibs, identify safer coxibs, as well as elucidate the roles of COX-2 and COX-1 in cardiovascular diseases and stroke in the hope that there may be some basis for developing newer agents (e.g. nitric oxide-donating NSAIDs) to control these conditions. The discovery of the COX isoforms led to establishing their importance in many non-arthritic or non-pain states where there is an inflammatory component to pathogenesis, including cancer, Alzheimer's and other neurodegenerative diseases. The applications of NSAIDs and the coxibs in the prevention and treatment of these conditions as well as aspirin and other analogues in the prevention of thrombo-embolic diseases now constitute one of the major therapeutic developments of the this century. Moreover, new anti-inflammatory drugs are being discovered and developed based on their effects on signal transduction and as anti-cytokine agents and these drugs are now being heralded as the new therapies to control those diseases where cytokines and other nonprostaglandin components of chronic inflammatory and neurodegenerative diseases are manifest. To a lesser extent safer application of corticosteroids and the applications of novel drug delivery systems for use with these drugs as well as with NSAIDs also represent newer technological developments of the 21st century. What started out as drugs to control inflammation, pain and fever in the last two centuries now has exploded to reveal an enormous range and type of anti-inflammatory agents and discovery of new therapeutic targets to treat a whole range of conditions that were never hitherto envisaged.

Cyclic nucleotide phosphodiesterases as targets for treatment of haematological malignancies

The cAMP signalling pathway has emerged as a key regulator of haematopoietic cell proliferation, differentiation and apoptosis. In parallel, general understanding of the biology of cyclic nucleotide PDEs (phosphodiesterases) has advanced considerably, revealing the remarkable complexity of this enzyme system that regulates the amplitude, kinetics and location of intracellular cAMP-mediated signalling. The development of therapeutic inhibitors of specific PDE gene families has resulted in a growing appreciation of the potential therapeutic application of PDE inhibitors to the treatment of immune-mediated illnesses and haematopoietic malignancies. This review summarizes the expression and function of PDEs in normal haematopoietic cells and the evidence that family-specific inhibitors will be therapeutically useful in myeloid and lymphoid malignancies.

Fatty acids and immune responses--a new perspective in searching for clues to mechanism

Dietary essential fatty acids are the precursors for eicosanoids. Among the eicosanoids derived from arachidonic acid, prostaglandin (PG) E2 is known to possess immunosuppressive actions. Thus, it has been a prevailing hypothesis that the immuno-modulatory roles of dietary fatty acids are mediated at least in part through the alteration of PG biosynthesis. PGs exert their biological effects through their cognate receptors. There are four subtypes of PGE receptors (EP1, EP2, EP3, and EP4) so far identified. Although the association of EP receptors with G proteins coupled to adenylate cyclase and the mobilization of intracellular calcium are well documented, downstream signaling pathways for these receptors are virtually unknown. Identification of downstream signaling pathways for each subtype of EP receptors and target genes regulated by the activation of the receptor will help with our understanding of the mechanism by which dietary fatty acids affect immune responses through the modulation of PGE2 biosynthesis. Emerging evidence suggests that fatty acids can additionally act as second messengers, regulators of signal transducing molecules or transcription factors. Acylation with long-chain fatty acids can occur on a variety of signaling molecules and can affect their membrane translocation and functions. Dietary fatty acids can alter functional properties of lipid mediators by changing the composition of acyl moieties of these molecules. Evidence accumulated recently indicates that long-chain unsaturated fatty acids and their metabolites bind and activate peroxisome proliferator-activated receptors (PPARs). PPARs are nuclear hormone receptors and transcription factors that regulate the expression of broad arrays of genes involved not only in lipid and glucose metabolism, but also in immune and inflammatory responses. PPARs may therefore be important cellular targets that mediate modulation of immune responses by dietary fatty acids. Together, it becomes clear now that multiple steps in various receptor-mediated signaling pathways can be modulated by dietary fatty acids. It will be a challenging task to quantitatively determine how different fatty acids alter functional properties of multitude of signaling components and final cellular responses. Elucidating the mechanism of actions of fatty acids on receptor-mediated signaling pathways in immuno-competent cells will provide a new insight for understanding the immuno-modulatory roles of dietary fatty acids.

Opposing effects of prostaglandin E(2)and F(2 alpha) on rat liver-associated natural killer cell activity in vitro

Strain differences in cancer incidence are proposed to be due partly to differences in immune function. As potential cancer-associated immunological regulators, the concentrations of hepatic prostaglandins E(2)(PGE(2 alpha)and F(2 alpha)(PGF(2 alpha)) were compared in 9-week-old male and female F344/N and Sprague-Dawley (SD) rats. There were no strain or gender differences in the concentrations of hepatic PGE(2). No strain difference was found in the concentration of hepatic PGF(2 alpha), but the hepatic PGF(2 alpha)concentration in female rats was two-fold that of the male rat (130 vs 60 ng/g). PGE(2)significantly inhibited hepatic natural-killer cell (NK) activity in vitro compared with untreated cells from both genders and strains (P<0.05), 25 ng PGE(2)/ml inhibited NK activity significantly more than did 10 ng PGE(2)/ml (P<0.05). In contrast, 50 ng PGF(2 alpha)/ml and 100 ng PGF(2 alpha)/ml significantly stimulated hepatic NK activity compared with untreated hepatic cells from both F344/N and SD rats. This study suggests that prostaglandins may have a negligible net effect on NK activity associated with rat liver, and may be unlikely to mediate cancer-related immune function.

Effects of some 1,4-dihydropyridine Ca antagonists on the blast transformation of rat spleen lymphocytes

Ca antagonists of different classes (verapamil, nifedipine, nicardipinc, diltiazem) in a concentration of 10(-5) M and higher are known to suppress Ca2+ transport into the lymphocyte cytosol, changing a normal response of lymphocytes to mitogens and antigens and so inhibiting their proliferation, as well as IL-2-induced cell proliferation, and their receptor expression on the surface of lymphocytes without cell cytotoxicity. In the present work we studied the effect of some 1, 4-dihydropyridines (DHP) such as nimodipine, nicardipine, nifedipine, niludipine, cerebrocrast, etaftoron, as well as metabolites of cerebrocrast: compounds 7 and 8, (four of the last were synthesized in the Latvian Institute of Organic Synthesis) on rat spleen isolated lymphocyte activation and proliferation in vitro following stimulation with the mitogens concanavalin A (Con A) and recombinant interleukin-2 (IL-2), insulin and insulin antibodies. Based on the experimental results we conclude that in low concentrations (10(-7) to 10(-9) M) the tested 1, 4-DHP Ca antagonists stimulated the process of rat spleen lymphocyte proliferation and DNA synthesis, especially cerebrocrast. It is proposed that these Ca antagonists, as well as causing a concentration decrease of Ca2+, also activated phosphodiesterase, which in its turn, suppressed cAMP accumulation in the lymphocytes and eventually increased Ca2+ ion transport in the cells. Cerebrocrast among all the studied DHP Ca antagonists was the most potent in studies of activation of the lymphocytes in the presence of Con A, IL-2 and insulin, which indicates the number of suppressor and helper lymphocytes and formation of insulin and interleukin receptors on their membrane surface. The increase in the lymphocytes suppressive activity produced by this compound effect can prevent diabetes mellitus types I and II at the stages of pre-diabetes, early and distant diabetes, from hyperexpression of insulin and its receptor antibodies.

The structure and function of CD26 in the T-cell immune response

CD26 is a widely distributed 110 kD cell-surface glycoprotein with known dipeptidyl-peptidase IV (DPP-IV) activity in its extracellular domain. This ecto-enzyme is capable of cleaving amino terminal dipeptides from polypeptides with either L-proline or L-alanine in the penultimate position. On human T cells, CD26 expression appears late in thymic differentiation and is preferentially restricted to the CD4+ helper/memory population, and CD26 can deliver a potent co-stimulatory T-cell activation signal. The cDNA sequence of CD26 predicts a type II membrane protein with only 6 amino acids in its cytoplasmic region, suggesting that, in addition to DPP-IV enzyme activity, other signal-inducing molecules may be associated with CD26. Considerable evidence exists that CD26 interacts, presumably in its extracellular domain, with both CD45, a protein tyrosine phosphatase, and adenosine deaminase (ADA), each of which is capable of functioning in a signal transduction pathway. In addition, CD26 is the receptor for ADA, and ADA on the cell surface is involved in an important immunoregulatory mechanism by which released ADA binds to the cell-surface ADA. This multifunctional molecule may be involved in cell migration and the HIV-1-associated loss of CD4+ cells through the process of programmed cell death. Thus, CD26 appears to play a key role in a number of aspects of lymphocyte function.

Role of A2a Extracellular Adenosine Receptor-Mediated Signaling in Adenosine-Mediated Inhibition of T-Cell Activation and Expansion

Accumulation of adenosine and of deoxyadenosine in the absence of adenosine deaminase activity (ADA) activity results in lymphocyte depletion and in severe combined immunodeficiency (ADA SCID), which is currently explained by direct cell death-causing effects of intracellular products of adenosine metabolism. We explored the alternative mechanisms of peripheral T-cell depletion as due to inhibition of T-cell expansion by extracellular adenosine-mediated signaling through purinergic receptors. The strong inhibition of the T-cell receptor (TCR)-triggered proliferation and of upregulation of interleukin-2 receptor α chain (CD25) molecules, but not the direct lymphotoxicity, were observed at low concentrations of extracellular adenosine. These effects of extracellular adenosine (Ado) are likely to be mediated by A2a receptor-mediated signaling rather than by intracellular toxicity of adenosine catabolites, because (1) poorly metabolized adenosine analogs cause the accumulation of cAMP and strong inhibition of TCR-triggered CD25 upregulation; (2) the A2a, but not the A1 or A3, receptors are the major expressed and functionally coupled adenosine receptors in mouse peripheral T and B lymphocytes, and the adenosine-induced cAMP accumulation in lymphocytes correlates with the expression of A2a receptors; (3) the specific agonist of A2a receptor, CGS21680, induces increases in [cAMP]i in lymphocytes, whereas the specific antagonist of A2a receptor, CSC, inhibits the effects of Ado and CGS21680; and (4) the increases in [cAMP]i mimic the adenosine-induced inhibition of TCR-triggered CD25 upregulation and splenocyte proliferation. These studies suggest the possible role of adenosine receptors in the regulation of lymphocyte expansion and point to the downregulation of A2a purinergic receptors on T cells as a potentially attractive pharmacologic target.

Role of A2a Extracellular Adenosine Receptor-Mediated Signaling in Adenosine-Mediated Inhibition of T-Cell Activation and Expansion

Accumulation of adenosine and of deoxyadenosine in the absence of adenosine deaminase activity (ADA) activity results in lymphocyte depletion and in severe combined immunodeficiency (ADA SCID), which is currently explained by direct cell death-causing effects of intracellular products of adenosine metabolism. We explored the alternative mechanisms of peripheral T-cell depletion as due to inhibition of T-cell expansion by extracellular adenosine-mediated signaling through purinergic receptors. The strong inhibition of the T-cell receptor (TCR)-triggered proliferation and of upregulation of interleukin-2 receptor α chain (CD25) molecules, but not the direct lymphotoxicity, were observed at low concentrations of extracellular adenosine. These effects of extracellular adenosine (Ado) are likely to be mediated by A2a receptor-mediated signaling rather than by intracellular toxicity of adenosine catabolites, because (1) poorly metabolized adenosine analogs cause the accumulation of cAMP and strong inhibition of TCR-triggered CD25 upregulation; (2) the A2a, but not the A1 or A3, receptors are the major expressed and functionally coupled adenosine receptors in mouse peripheral T and B lymphocytes, and the adenosine-induced cAMP accumulation in lymphocytes correlates with the expression of A2a receptors; (3) the specific agonist of A2a receptor, CGS21680, induces increases in [cAMP]i in lymphocytes, whereas the specific antagonist of A2a receptor, CSC, inhibits the effects of Ado and CGS21680; and (4) the increases in [cAMP]i mimic the adenosine-induced inhibition of TCR-triggered CD25 upregulation and splenocyte proliferation. These studies suggest the possible role of adenosine receptors in the regulation of lymphocyte expansion and point to the downregulation of A2a purinergic receptors on T cells as a potentially attractive pharmacologic target.

VIP modulation of immune cell functions

Neuropeptides have recently been shown to modulate the immune response. Vasoactive intestinal peptide (VIP) released from nerve endings and from immune cells modulates the mobility and adherence of lymphocytes and macrophages, phagocytic cell functions (phagocytosis and free radical production), the lymphocyte proliferative response, lymphokine and immunoglobulin production and the natural killer cell activity, with opposite effects in vitro on these immune cell functions. The VIP receptor heterogeneity and the different action mechanisms of VIP-mediated immunoregulation could explain, at least in part, the different VIP effects observed on lymphoid and phagocytic cells. The evidence supports the theory that VIP acts not as an inhibitor, but as a modulator of immune functions, as previously thought, and that this neuropeptide may play a relevant role in vivo.

The role of adrenoceptor-mediated signals in the modulation of lymphocyte function

Adrenoceptors are heterotrimeric glycoproteins that bind specific endogenous ligands, such as the sympathetic neurotransmitter norepinephrine and the neurohormone epinephrine. Ligand binding to an adrenoceptor expressed on the cell surface initiates a cascade of biochemical and molecular responses inside the cell that lead to a change in cellular activity. Initially, the stimulation of an adrenoceptor directly activates G proteins that stimulate enzymes to induce the production of second messengers. The cascade continues as the second messengers activate serine/threonine protein kinases, resulting in either an inhibition or enhancement of cellular activity. The resulting changes in cellular activity are mediated by changes in gene expression that are induced by the phosphorylation of specific transcription factors. Adrenoceptor subtypes are expressed by both T and B lymphocytes. The aim of this review is to summarize and discuss the results from the many studies that have examined the role of adrenoceptor-mediated intracellular signals in the modulation of lymphocyte function. Another aim of this review is to discuss how these studies have advanced our understanding of the mechanisms by which the sympathetic nervous system transmits information to both T and B lymphocytes to maintain immune homeostasis.

Preclinical studies of antitumor prostaglandins by using human ovarian cancer cells

Pleiotropic actions of antitumor prostaglandins (PGs) on tumor cells are reviewed including our preclinical results focused on human ovarian cancer. Regarding inhibition of cell proliferation, antitumor PGs exerts its action as a G1 blocking agent. The cyclopentenone PGs inhibit myc oncogene expression while inhibiting the cell cycle progression and results in apoptotic cell death and growth inhibition. Cyclopentenone PGs inhibit growth of various tumors transplanted to mice or nude mice and show adjuvant effects to cis-diamminedichloroplatinum(II) (CDDP). In order to elucidate a role of antitumor PGs in immune systems, relevance of effects on tumor growth with those on the immune systems are also discussed with our results.

Characterization of a murine central nervous system-derived cell line: infectability and presentation of viral antigen

The cerebral endothelial cell line, 33-Mse, was characterized for its MHC antigen expression, infectability with viruses and capacity to present antigen to immune spleen cells. The cell line had interferon-gamma inducible MHC antigen expression. Infection by Theiler's murine encephalomyelitis influenced the expression of MHC molecules on the cell surface of this line. These cells could not stimulate T splenocyte proliferation or act as targets for Theiler's murine encephalomyelitis cytolytic immune spleen cells. These cells were able to present viral antigen to vaccinia virus immune spleen cells and act as targets for cytotoxic T cells from vaccinia virus immune mice.

Effect of PGE2 on thymocyte proliferation induced by Con A or IL-4 + PMA

Prostaglandin E2 (PGE2) is known to inhibit peripheral T-lymphocyte and thymocyte proliferation activated by antigens, mitogens or anti-CD3 antibodies. In this study, we have investigated, the effect of PGE2 on thymocyte proliferation induced by the combination of IL-4 plus PMA. PGE2 inhibits the proliferation of thymocytes activated by ConA, whatever the culture period; in contrast PGE2 shifts the kinetics of thymocyte proliferation after stimulation by IL-4 plus PMA, but does not sustain the proliferation beyond day 3. This effect depends upon cell density, IL-4 concentration and on the time that PGE2 is added to the culture. By use of the cAMP inducer, forskolin, or a cAMP analog, db-cAMP, we observed the same results, PGE2 increases the proliferation of CD8+ corticoresistant thymocytes (CRT) activated by IL-4 plus PMA, but inhibits that of CD4+ CRT. These results suggest that PGE2 can regulate thymocyte proliferation differently according to the activation pathway and the thymic subpopulations.

Borage or primrose oil added to standardized diets are equivalent sources for gamma-linolenic acid in rats

The aim of this study was to evaluate the effect of different doses and sources of dietary gamma-linolenic acid (GLA) on the tissue phospholipid fatty acid composition. Rats fed four different levels of GLA (2.3, 4.6, 6.4 and 16.2 g of GLA/kg diet) in the form of either borage oil or evening primrose oil during 6 wk were compared with animals fed corn oil. The levels of dihomo-gamma-linolenic acid (DHLA) and GLA showed a significant dose-related increase in liver, erythrocyte and aorta phospholipids. Moreover, the arachidonic acid/DHLA ratios in tissues decreased with increasing intake of dietary GLA. There was no significant difference in tissue GLA and DHLA levels within groups given equal amounts of dietary GLA either as borage oil or evening primrose oil. The amount of dietary GLA administered did not significantly influence prostaglandin E2 production in stimulated aortic rings and thromboxane B2 levels in serum; however, an increase in prostaglandin E1 derived from DHLA was observed in the supernatants of stimulated aorta.

Cholinergic and adrenergic drugs affect delayed type hypersensitivity in C57BL/6 mice

The present study examined the influence of systemic administration of neuroactive drugs on delayed-type hypersensitivity (DTH) in C57BL/6 mice. The cholinergic agonist nicotine and the acetylcholinesterase inhibitor physostigmine decreased DTH, whereas the alpha-adrenergic agonist clonidine stimulated DTH. In contrast isoprenaline, a specific beta-adrenergic agonist suppressed DTH. It is concluded from these observations that the autonomic nervous system modulates those processes governing DTH. It seems that the alpha-adrenergic subsystem stimulates, whereas the beta-adrenergic subsystem and the parasympathicus inhibit DTH.

Methylxanthine-induced inhibition of the antigen- and superantigen-specific activation of T and B lymphocytes

Methylxanthines have been shown to have a variety of effects on hematopoietic cell activation and function. These compounds inhibit cAMP-specific phosphodiesterase activity resulting in increased levels of intracellular cAMP. In the present study, we examined the effects of two methylxanthines, pentoxifylline (PTX) and caffeine, on the responses of both mouse and human lymphocytes to stimulation with polyclonal T- and B-cell mitogens, antigens, and the microbial superantigen, staphylococcal enterotoxin B (SEB). Both PTX and caffeine significantly inhibited mitogen- and SEB-induced proliferation by murine spleen cells, SEB- and antigen-induced proliferation and lymphokine secretion by murine Th1 and Th2 clones, and the generation of antigen-specific antibody producing murine spleen cells. These compounds also inhibited the proliferative responses of human lymphocytes to phytohemagglutinin, SEB, and tetanus toxoid. Efforts to determine whether these methylxanthine compounds mediated their inhibitory effects through a specific protein kinase pathway revealed a role for cAMP-dependent protein kinase A in methylxanthine-induced immunomodulation. However, it is possible that a protein kinase A-independent pathway may also be involved. These data demonstrate that the methylxanthines, PTX and caffeine, have profound effects on cells of the immune system and may have a potential use as immunotherapeutic agents in the treatment of various inflammatory conditions and autoimmune diseases.

Production of soluble autocrine inhibitory factors by human glioma cell lines

Gliomas in vitro exhibit density-limited growth upon the attainment of confluency, an effect usually attributed to cell-cell contact inhibition. Since gliomas have been demonstrated to secrete an array of soluble factors which can enhance tumor growth, we undertook this study to ascertain whether production of soluble factors by the tumor may also inhibit growth in an autocrine manner, and whether production of such factors is associated with the growth phase of the glioma. We observed that cell-conditioned medium (supernatants) from non-confluent glioma cultures induced growth, while confluent culture supernatants produced pronounced growth suppression. These latter supernatants enhanced proliferation of non-transformed astrocytes. Supernatants derived from all stages of confluency produced inhibition of lymphocyte proliferation. To characterize these factors, dialyzed supernatant was tested and found to continue to produce lymphocyte suppression but no glioma growth limitation. Growth of tumors in indomethacin or in acetylsalicylic acid to abolish prostanoid synthesis abrogated the inhibitory influence on glioma growth but only partially reversed the lymphocyte suppressive capacity. These studies suggest that gliomas do produce a growth phase dependent autocrine inhibitory factor(s), and that the production of these small molecular weight factors is at least partially under control of the cyclooxygenase pathway.

Leukotriene B4 in the immune system

Leukotriene (LT) B4 is a biologically active molecule derived from arachidonic acid via the 5-lipoxygenase pathway. It mediates certain inflammatory and immunological reactions. The role of LTB4 in the immune system has been questioned since lymphocytes have been regarded to lack the enzymes involved in LTB4 formation. This review focuses on the recently described biosynthesis of LTB4 in B-lymphocytes and the effects of this compound on lymphocyte functions.

The inhibition of T-lymphocyte proliferation by fatty acids is via an eicosanoid-independent mechanism

Eicosanoids, in particular prostaglandin E2 (PGE2), are potent inhibitors of a number of immune responses, including lymphocyte proliferation. We have previously shown that fatty acids, especially polyunsaturated fatty acids (PUFA), inhibit mitogen-stimulated proliferation of lymphocytes. One mechanism by which fatty acids could exert their inhibitory effect is via modulation of eicosanoid synthesis. This possibility was investigated in the present study. PGE2 concentrations in the medium taken from lymphocytes cultured in the presence of a range of different fatty acids did not correlate with the inhibitory effects of the fatty acids upon lymphocyte proliferation. Although PGE2 at concentrations above 10 nM caused inhibition of lymphocyte proliferation, PGE2 at the concentration measured in lymphocyte culture medium (0.3-4 nM) was not inhibitory. PGE3 did not inhibit lymphocyte proliferation, except at high concentrations (greater than 250 nM). The maximal inhibition of proliferation caused by PGE2 or PGE3 was less than the inhibition caused by each of the fatty acids except myristic or palmitic acids. Inclusion of inhibitors of phospholipase A2, cyclo-oxygenase or lipoxygenase in the culture medium did not prevent the fatty acids from exerting their inhibitory effect on lymphocyte proliferation. The eicosanoids present in lymph node cell cultures originate from macrophages rather than lymphocytes. Depletion of macrophages from the cell preparation by adherence did not prevent fatty acids from inhibiting proliferation. Proliferation of thoracic duct lymphocytes, which are devoid of macrophages, is inhibited by fatty acids to a similar extent as proliferation of lymph node lymphocytes. These observations provide convincing evidence that the inhibition of lymphocyte proliferation by fatty acids is independent of the production of eicosanoids. Therefore, other mechanisms must be investigated if the effect of fatty acids upon lymphocyte proliferation is to be understood at a biochemical level.

Modulation of human lymphocyte response to phytohemagglutinin by antineoplastic prostaglandins

The effects of antineoplstic prostaglandins (PGs) (PGE1, PGE2, PGA1, PGA2, delta 7-PGA1, PGD2, PGJ2 and delta 12-PGJ2) on human peripheral blood lymphocyte (PBL) responses to phytohemagglutinin (PHA) were studied in vitro. All PGs used in this study alone had no mitogenic effect on the PBL. The PBL response to PHA was significantly stimulated at low concentrations (10(-7) and 10(-8) M) of the PGE series while the high concentration (10(-5) M) markedly inhibited the PHA response. PGA1 and PGA2, metabolites of the PGE series, and also delta 7-PGA1 stimulated the PHA response in a dose-dependent manner between 10(-6) and 10(-8) M, and showed a significant stimulatory effect at 10(-6) M while significantly inhibiting the PHA response at 10(-5) M. Similarly, 10(-6) and 10(-7) M (but not 10(-8) M) of PGD2 stimulated significantly the PHA response. PGJ2 and delta 12-PGJ2, which are metabolites of PGD2, also stimulated the PHA response in a dose-dependent manner between 10(-6) and 10(-8) M, and had a significant stimulatory effect at 10(-6) and 10(-7) M. The degree of the stimulatory effect was most marked with the PGD2 series among the antineoplastic PGs examined in this study. On the other hand, PGs (PGF1 alpha and PGF2 alpha) having no antineoplastic effect did not show such effects on the PHA response. These results suggest that antineoplastic PGs may have immunoregulatory effects through negative and positive feedback.

Cyclic adenosine monophosphate-stimulating agents induce ecto-5'-nucleotidase activity and inhibit DNA synthesis in rat cultured mesangial cells

The ecto-5'-nucleotidase activity of rat glomerular mesangial cells increases after exposure to prostaglandin E2 (PGE2) via cAMP stimulation (Savic et al., 1990, Immunology 70, 321). Therefore we examined whether other cAMP-stimulating agents had a similar effect. Forskolin (1 microM), PGE2 (10 microM), and isoproterenol (10 microM), three products stimulating rat mesangial cell adenylate cyclase activity, enhanced cAMP accumulation within 5 min and 5'-nucleotidase activity after a lag time of at least 24 h, 3-Isobutyl-1-methylxanthine (IBMX) and Ro 20-1724, two drugs inhibiting cAMP degradation, also stimulated cAMP accumulation and 5'-nucleotidase activity. The effects of these agents on 5'-nucleotidase activity were additive with those of the three products stimulating adenylate cyclase activity, except for Ro 20-1724 and forskolin which acted synergistically. Cycloheximide, a blocker of protein synthesis, suppressed the cAMP-dependent increase of 5'-nucleotidase activity. Because ecto-5'-nucleotidase activity is a marker of cell differentiation, the effect of the same cAMP-stimulating agents on cell proliferation was also studied. Forskolin, PGE2, and isoproterenol inhibited [3H]thymidine incorporation into rat mesangial cells in a dose-dependent manner. The same effect was obtained with IBMX (100 microM) and Ro 20-1724 (50 microM). Stimulation of 5'-nucleotidase activity and inhibition of [3H]thymidine incorporation occurred over the same range of concentrations for the various agonists tested. Taken together, these results indicate that expression of ecto-5'-nucleotidase in rat mesangial cells is induced by cAMP whatever the reason for its accumulation. The simultaneous inhibition of DNA synthesis may occur independently or be associated with the stimulation of 5'-nucleotidase expression.

Differential Sensitivity of CD4+ and CD8+ T Lymphocytes to Phorbol Myristate Acetate upon Anti-CD3 Stimulation: Evidence for a Distinct Signaling Pathway

The effects of suboptimal concentrations of Phorbol Myristate Acetate (PMA) in combination with submitogenic concentrations of OKT3 antibody on CD4+ and CD8+ cell activation were investigated. Upon stimulation with OKT3 (25 pg/ml) and PMA (0.25 – 0.75 ng/ml), the majority of CD4+ cells entered the cell cycle whereas most of CD8+ cells remained in G0/G1 phase. Under the same conditions of OKT3 stimulations, both CD4+ and CD8+ cells failed to produce IL2 in the absence of PMA. In the presence of PMA (0,25 ng/ml), CD4+ produced measurable amounts of IL2 (0,5 – 2,3 U/ml) whereas IL2 production by CD8+ cells remained below the detection limit. Expression of TAC antigen (CD25) was found to parallel IL2 production and cell proliferation in both subsets whereas changes in [Ca2+] mobilization following OKT3 stimulation were similar in both subsets.

Interestingly, the elevation of intracellular cyclic adenosine 3':5' monophosphate (cAMP) was not equally distributed between CD4+ and CD8+ subpopulations. Furthermore, the kinetics of protein kinase (PKC) translocation was markedly prolonged in membranes of CD4+ cells compared with CD8+ cells suggesting a differential involvement that may operate under distinct regulatory signaling mechanisms.

Involvement of cyclic adenosine monophosphate in the interleukin 4 inhibitory effect on interleukin 2-induced lymphokine-activated killer generation

In previous studies, IL-4 has been reported to interfere with IL-2-driven generation of lymphokine-activated killer (LAK) activity. In this investigation, we have demonstrated that IL-4 inhibited the IL-2-induced differentiation of large granular lymphocytes (LGL) into LAK effectors by a mechanism involving, at least in part, an increase in LGL intracellular cAMP levels. In contrast, with its capacity to induce cAMP accumulation in resting LGL, IL-4 had a very negligible effect on LAK activity induction, and cAMP levels increase in LGL that had been preincubated with IL-2. Furthermore, the inhibitory effect of IL-4 on LAK activity generation also correlated with a marked decrease in N-CBZ-L-lysine thiobenzylester esterase activity, with an inhibition of tumor necrosis factor (TNF) mRNA expression and TNF production by IL-2-stimulated LGL. These results strongly suggest that complex signaling processes could be ascribed to the dual activities of cytokines and their interplay in LAK promotion.

Influence of PGE2- and cAMP-modulating agents on human glioblastoma cell killing by interleukin-2-activated lymphocytes

Human glioblastoma cells secrete factors, such as prostaglandin E (PGE) and transforming growth factor beta type 2, which are capable of suppressing several immune functions. The present study investigated the effect of PGE2 and agents known to increase intracellular cyclic adenosine monophosphate (cAMP) levels on 1) the induction of lymphokine-activated killer (LAK) cell activity from the peripheral blood lymphocytes (PBL) of both normal and glioma patients and on 2) the cytolytic activities of tumor-infiltrating lymphocytes (TIL's) isolated from malignant gliomas after expansion in vitro with interleukin-2 (IL-2). Cytolytic activity was measured against autologous and allogeneic tumor cells and the natural killer-resistant Daudi cell line. The results demonstrate that PGE2 and agents known to increase intracellular cAMP levels can significantly suppress the IL-2-dependent generation of cytolytic activity from the PBL of normal and glioma patients and from glioblastoma-derived TIL's. The inhibitory effects of these agents could not be reduced by higher concentrations of IL-2 or by cyclic guanosine monophosphate. Although the suppressive effect of PGE2 was most significant during the early stages of LAK cell generation, an inhibitory effect was still evident when PGE2 was added directly to the cytotoxicity assay. Secretion of PGE2 by glioblastoma cells in vivo may regulate both the generation of an immune response and the effectiveness of adoptively transferred immune cells.

Elevation of cyclic adenosine monophosphate levels independently down regulates IL-1, IL-2, and IL-2 receptor (CD25) syntheses

In view of the central involvement of interleukin-1 (IL-1) in T-cell functions and the negative effects exerted by cyclic adenosine monophosphate (cAMP) on T-cell responses, we wondered whether these inhibitions rely on defects in IL-1 generation. We investigated the effect of a known cAMP elevating agent, cholera toxin (CT), on the generation of IL-1 from peripheral blood adherent cells as well as the role of IL-1 whenever IL-2 synthesis and IL-2 receptor (CD25 antigen) expression are inhibited. While augmenting intracellular cAMP concentration, CT inhibits from 20 to 40% the generation of IL-1 activity from E. coli lipopolysaccharide (LPS)-stimulated adherent cells. Theophylline (TH), a cAMP degradation blocking agent, induces the same decrease in IL-1 activity. The B chain of CT, devoid of cAMP activating potency, is not inhibitory. In systems where CT and TH dramatically inhibit the generation of IL-2 activity (80%), addition of exogenous IL-1 does not restore the ability of T-cells to produce or release IL-2. Moreover, CT- and dibutyryl (db)cAMP-induced inhibition of CD25 antigen expression is not overcome by exogenous IL-1, IL-2, nor by both interleukins. It is concluded that inhibition of IL-1 and IL-2 production are independent and that inhibition of CD25 antigen expression is independent of IL-1 and IL-2 modulation. Cholera toxin and cAMP influences on interleukin synthesis are discussed.

Neurotransmitter-lymphocyte interactions: dual receptor modulation of lymphocyte proliferation and cAMP production

Stimulation of the beta-adrenergic receptor on lymphocytes can decrease the proliferative response of these cells to mitogens. We have found that simultaneous stimulation of T cells with the beta-adrenergic agonist isoproterenol and mitogens (phytohemagglutinin (PHA) and OKT3 monoclonal antibody) results in a 2- to 4-fold increase in cAMP production compared to cells exposed to isoproterenol alone. Mitogens alone have little effect on cAMP synthesis, but do activate the phosphatidylinositol (PI) cycle, suggesting that interactions may be occurring between the second messenger systems resulting in a cAMP synergy. Further experiments suggest that calcium may be involved in inducing the cAMP synergy observed in T cells. It is proposed that the synergy between beta-adrenergic and mitogenic stimulation of T cells for cAMP may be involved in the mechanism of catecholamine modulation of lymphocyte function.

The levels and relations of prostaglandins in pregnant and non-pregnant tumor-bearing mice

Tissue levels of prostaglandins PGE1, PGE2, PGF1 alpha and PGF2 alpha were determined in muscle tissues of pregnant, and in tumor tissue of pregnant tumor-bearing female syngeneic Balb/c mice bearing a transplanted methylcholanthrene-induced fibrosarcoma. Tests were done on the 7th, 10th, and 15th days of tumor growth/pregnancy using a thin-layer chromatography method. The results showed significantly increased levels of prostaglandins in tumor-bearing animals as well as in pregnant tumor-bearing hosts when compared to controls. Changes in the levels of PGE1 in pregnant mice were the most prominent among all prostaglandins tested. In these animals, the mutual relations between prostaglandin subclasses were not affected. In tumor-bearing mice, especially those which were pregnant, the inversion of prostaglandins of the E series was observed. Tumor changed the levels of the E series prostaglandins in favour of PGE2. However, it did not change the relation between those of the F series. The levels of PGE2 were more expressed in pregnant tumor-bearing hosts than in their non-pregnant counterparts. This has led us to the conclusion that, besides the malignant tumor, the pregnancy itself also potentiates immunosuppression. Blocking of PGE2 production in tumor-bearing animals might have potential therapeutic implications.

Lipid mediator production by post-implantation rat embryos in vitro

The production of inflammatory lipid mediators by post-implantation rodent embryos was examined in this study. Explanted day 10 rat embryos, either intact or after homogenization, were cultured for 3 hr in vitro and the resulting culture medium and embryonic tissue were assessed for eicosanoids and platelet-activating factor (PAF). The rank order of cyclooxygenase arachidonate products produced by intact embryos was as follows: 6-keto-PGF1 alpha much greater than congruent to PGF2 alpha congruent to TXB2. No lipoxygenase products of arachidonic acid metabolism were detected by either high performance liquid chromatography or radioimmunoassay. PAF production was detectable in embryonic cultures. Homogenization of rat embryos prior to in vitro culture enhanced eicosanoid and PAF production from 2.1-6.9 fold over intact embryos. These findings demonstrate the extent of lipid metabolism by early post-implantation rat embryos and support the concept that potent lipid mediators of inflammation generated by the conceptus may play a role in both the initiation and maintenance of pregnancy.

Antigen presentation in brain: brain endothelial cells are poor stimulators of T-cell proliferation

The capacity of rat brain capillary endothelium to present antigen to primed peripheral lymph node cells or to ovalbumin-specific T-cell lines was examined in vitro. Brain endothelium can present antigen, but it is generally ineffective at stimulating T-cell division. Division is only seen when indomethacin is included in the cultures to suppress eicosanoid production. Even under these conditions an endothelial monolayer is only 1/40 as effective as a thymocyte monolayer in stimulating division. The failure to act as an effective antigen presenting tissue is not due to lack of IL-1 production, nor is it related to the extended time required to induce MHC class II molecules on these cells. In the presence of high levels of antigen-specific T cells, the endothelium appears to be subject to cytotoxic damage, so that T-cell stimulation is lowest with higher numbers of T cells--the opposite of that seen with conventional antigen-presenting cells. These findings support the view that brain endothelial cells are not important in stimulating T-cell division during the development of immune reactions in brain, although these cells may be recognizable by class II-restricted cytotoxic cells.

The functional deficiency of B lymphocytes in patients with lung cancer is due to inadequate T-cell help and excessive suppression by T and non-T cells

The proliferative and plaque-forming cell (PFC) responses of unseparated mononuclear cells (MNC) and B- and T-cell-enriched populations of cells were analyzed in 15 patients with lung cancer to determine the mechanisms involved in the functional abnormality of their B cells. The PFC responses of the MNC of the patient group were significantly lower than those of normal controls. In addition, the enriched B cells of several patients showed a further decrease in their PFC responses after coculture with autologous T cells compared with their respective MNC responses. The proliferative response against phytohemagglutinin (PHA) was also lower in many of the patients after similar cocultures. Cocultures of patients' B cells with T cells from normal controls significantly enhanced the PFC responses in 7 patients. In most of the normal controls, B lymphocytes showed a significant decrease in their PFC responses after coculture with the patients' T cells. Although the percentages of total T cells, T-helper, and B cells were within the normal range, the number of suppressor T cells was significantly higher in the patient group. These results indicate that a combination of insufficient T-cell help, excessive suppression by both T and non-T cells, and a possible intrinsic B-cell abnormality are responsible for the B-cell functional deficiency observed in patients with lung cancer.

Regulation of proliferation in a murine colony-stimulating factor-dependent myeloid cell line: superinduction of c-fos by the growth inhibitor 8-Br-cyclic adenosine 3':5' monophosphate

We have investigated the effect of 8-Br-cyclic adenosine 3':5' monophosphate (cAMP), a pharmacological activator of cAMP-dependent protein kinase, on the proliferation and the nuclear proto-oncogene induction in a murine granulocyte macrophage colony-stimulating factor (GM-CSF)-dependent myeloid cell line. Cells were growth arrested by granulocyte macrophage colony-stimulating factor and serum deprivation and were allowed to proceed in the cell cycle by addition of the lymphokine in the presence or absence of 8-Br-cAMP. 3H-thymidine incorporation assays showed that addition of 8-Br-cAMP inhibited the entry of cells into S phase and the subsequent proliferation. Northern analysis showed that 8-Br-cAMP had opposite effects on c-fos and c-myc mRNA induction. 8-Br-cAMP induced c-fos in the absence of any GM-CSF. In the presence of GM-CSF, c-fos mRNA was superinduced (30-fold induction compared to four- to fivefold by each signal alone). On the contrary, 8-Br-cAMP was not able to induce c-myc in the absence of growth factor and hardly interfered with the induction of c-myc by GM-CSF. Phorbol myristate acetate (PMA), a pharmacological activator of the lipid and CA++-dependent protein kinase C, was shown to induce nuclear proto-oncogene mRNA in the GM-CSF-dependent cell line. We investigated the effect of 8-Br-cAMP on PMA-induced c-fos and c-myc mRNA levels. When both cAMP dependent and lipid-dependent kinase systems were co-stimulated in the absence of GM-CSF, c-fos message was again superinduced (60-fold induction). On the contrary, c-myc message induction by PMA was inhibited by 80% by coactivation of cAMP-dependent protein kinase with 8-Br-cAMP. Our data indicate that an antiproliferative signal induces or even superinduces c-fos message and hardly interferes with c-myc induction, suggesting that the intracellular pathways resulting in c-fos and c-myc induction may be distinct and that two different pathways can lead to c-fos induction, with synergistic effects when both are activated.

C-Reactive Protein (CRP) Modulates Lymphocyte Proliferation VIA Affecting Activation Step

The effect of CRP on lymphocyte activation and proliferation in vitro was estimated on the basis of measurement of 3H-thymidine incorporation, analysis of distribution of subsequent cell divisions and analysis of IL-2 receptor expression. Low doses of CRP (less than 3μg/ml) stimulated and high doses (over 5μg/ml) inhibited lymphocyte activation, with little effect on proliferating lymphoblasts. The presence of foetal bovine serum or autologous serum modified CRP action on lymphocytes. The inhibitory effect of CRP on lymphocyte proliferation was similar in cultures stimulated by PHA or by allogeneic cells. On the basis of results obtained, CRP is considered a possible immunomodulator.

Forskolin effects on the voltage-gated K+ conductance of human T cells

Forskolin, a direct activator of adenylate cyclase, modifies the voltage-dependent K+ conductance of quiescent human peripheral blood T lymphocytes. In the presence of greater than 20 microM forskolin, the average voltage-gated current in whole-cell patch clamp is significantly decreased. The voltage dependence and kinetics of activation are not changed from untreated control cells. However, inactivation becomes biphasic. Much of the current inactivates very quickly (complete in 10 ms), and the remaining outward current inactivates more slowly with a time constant closer to that of control cells. To determine whether this effect is mediated by a rise in intracellular cAMP, cells were preincubated and subsequently voltage-clamped in the presence of other agents that raise the cAMP levels in T cells (isoproterenol plus a phosphodiesterase inhibitor, or dibutyryl cAMP) with no effect on the K+ conductance. Similarly, cells put in whole-cell patch clamp with cAMP, GTP, ATP, and theophylline added to the electrode filling solution showed no change in K+ current. Because other procedures that raise cAMP did not duplicate the effect of forskolin, we investigated the effect of 1,9-dideoxyforskolin, an analogue of forskolin that does not stimulate adenylate cyclase in human lymphocytes. This drug induced changes in the whole-cell K+ conductance identical to those observed with forskolin. Both forskolin and dideoxyforskolin inhibit mitogen-induced proliferation of lymphocytes. Because inhibition of proliferation occurs in the presence of known K+ channel blockers, these results suggest that forskolin has an effect on T cell mitogenesis that is mediated by inhibition of K+ conductance and is independent of cAMP.

Purification and characterisation of an immunosuppressive factor from normal human seminal plasma

We have previously described the presence of a human seminal plasma component which may prevent the immunologic sensitization of females against sperm and seminal plasma antigens. Purification of the immunosuppressive factor (ISF) by saturated ammonium sulphate precipitation, followed by Sepharose 4-B column chromatography and Con-A Sepharose 4-B affinity chromatography is described here. An apparently single-band protein on SDS gel electrophoresis, having a molecular weight of 35,000, has been isolated. Amino acid analysis of this glycoprotein shows that it is rich in isoleucine, glycine, glutamine and proline, while methionine, tyrosine and asparagine are present in traces.

Modulating action of Escherichia coli heat-stable enterotoxin (STa) on the humoral immune response

The effect of Escherichia coli enterotoxin STa on the primary and secondary immune response in F1 (CBA x C57 B1/10) mice immunized against sheep red blood cells (SRBC) was investigated. Modulating action on the IgM and IgG response was found to be dependent on the dose-time administration of the toxin. Immunosuppression of the primary response on the 4th day after immunization was observed when the toxin was injected 15 min before the SRBC, followed by immunostimulation on the 6th day after antigen (Ag) injection. Moreover, toxin administration 48 h before SRBC caused immunosuppression of the primary immune response on the 4th and 6th days. On the other hand, the IgM and IgG secondary immune response, determined 6 days after boosting, was greatly enhanced by toxin administration 15 min before priming (day 0) or boosting (day 26) and 48 h before priming. The same response was suppressed by toxin administration 48 h before booster antigen injection.

Demonstration of the ability of Hofbauer cells to phagocytose exogenous antibodies

We have studied the effects of the anti-human chorionic gonadotropin and anti-human antithrombin III antibodies on Hofbauer cells from human immature placenta, when applied to either intact villi or on cell culture. Trypsin treatment of the villi results in a mixed cell culture mainly composed of isolated Hofbauer cells but which also contains a variable number of mesenchymal cells and a few syncytiotrophoblastic cells. In all samples analysed only 7-8% of the Hofbauer cells and some syncytiotrophoblastic cells exhibited a macrophagic activity 24 h after incubation of the cultures with the antisera. That only certain proportions of Hofbauer and syncytiotrophoblastic cells express macrophagic activity is also seen when intact villi are incubated for 24 h with these antibodies. Indeed, neither all the villi nor all these cells within a single villus are positively stained. The fact that only a fraction of Hofbauer cells and syncytiotrophoblast express a macrophagic activity may suggest that only some cells, amongst both these cell types, are involved in the protection of the fetus against maternal immunological rejection by removing immunological complexes.

Rectal infusion of semen results in transient elevation of blood prostaglandins

Repeated semen deposition in the gut may be linked to the development of viral infections in homosexual men. Other investigators have suggested that rectal insemination may diminish immune responsiveness. We approximated conditions of human insemination by infusing 2 ml of pooled human seminal plasma (SP) into the rectum and/or vagina of rhesus monkeys. This resulted in increased blood plasma concentrations of the bicycloderivative of prostaglandin E (PGEM-II) which reached peak concentrations 2 h after rectal SP instillation in seven of eight test monkeys, but not the controls. The rate of PGE2 diffusion appeared to occur more rapidly across vaginal than rectal mucosa. Suppression of peripheral cellular immune functions was not demonstrated after the single exposure of this study, although persistent and repeat exposures could lead to local or generalized suppression of host defense mechanisms. Absorption of PGE's from the gut may be a cofactor in the development of sexually transmitted viral diseases.