Observations on the Proliferation of Human Leucocytes Cultured with Phytohaemagglutinin

Metabolic optimization of adoptive T cell transfer cancer immunotherapy: A historical overview

After prolonged extracorporeal multiplication in physiological culture media, there can be curative infusions of a cancer patient's own cytotoxic T cells (adoptive T cell transfer; ACT), which must achieve efficient activation in potentially adverse tumour microenvironments. With spectacular, yet irregular, success, improvements are needed. Developing lymphoid cells are biologically selected, not only for 'near-self' reactivity (positive selection), but also to avoid self-reactivity (negative selection). Thus, success requires harnessing near-self cells while avoiding extreme autoimmune phenomena. Abrupt metabolic changes accompanying T cell activation to leave the G₀ stage and enter the G₁ stage of the cell cycle (eg enhanced glycolysis) are accompanied by increased transcription of the G0S9 gene that mediates salvage synthesis of NAD⁺ from nicotinamide; the latter has recently been shown to increase the efficiency of ACT. Despite theoretical and experimental advances, there has not been parallel progress in simulating in vivo conditions with culture media that were initially formulated for their positive benefits for tumour cell lines (cell survival and proliferation). Yet for lymphoid cells, inhibition or death (ie immunological tolerance) is as important as their activation and proliferation (immunological response). Thus, use of media optimized for the latter may mask the former. The resilience of established culture protocols may have been partly politically driven. However, unphysiological conditions have sometimes yielded fortuitous insights. Optimization of culture media for specific tissues must consider the nature of problems addressed in research settings and the need to avoid mishaps in clinical settings.

The immunologic Warburg effect: Evidence and therapeutic opportunities in autoimmunity

Pro‐inflammatory signals induce metabolic reprogramming in innate and adaptive immune cells of both myeloid and lymphoid lineage, characterized by a shift to aerobic glycolysis akin to the Warburg effect first described in cancer. Blocking the switch to aerobic glycolysis impairs the survival, differentiation, and effector functions of pro‐inflammatory cell types while favoring anti‐inflammatory and regulatory phenotypes. Glycolytic reprogramming may therefore represent a selective vulnerability of inflammatory immune cells, providing an opportunity to modulate immune responses in autoimmune disease without broad toxicity in other tissues of the body. The mechanisms by which aerobic glycolysis and the balance between glycolysis and oxidative phosphorylation regulate immune responses have only begun to be understood, with many additional insights expected in the years to come. Immunometabolic therapies targeting aerobic glycolysis include both pharmacologic inhibitors of key enzymes and glucose‐restricted diets, such as the ketogenic diet. Animal studies support a role for these pharmacologic and dietary therapies for the treatment of autoimmune diseases, and in a few cases proof of concept has been demonstrated in human disease. Nonetheless, much more work is needed to establish the clinical safety and efficacy of these treatments.

This article is categorized under:

Biological Mechanisms > Metabolism

Translational, Genomic, and Systems Medicine > Translational Medicine

Biological Mechanisms > Cell Signaling

Lactate dehydrogenase and glycerol-3-phosphate dehydrogenase cooperatively regulate growth and carbohydrate metabolism during Drosophila melanogaster larval development

The dramatic growth that occurs during Drosophila larval development requires rapid conversion of nutrients into biomass. Many larval tissues respond to these biosynthetic demands by increasing carbohydrate metabolism and lactate dehydrogenase (LDH) activity. The resulting metabolic program is ideally suited for synthesis of macromolecules and mimics the manner by which cancer cells rely on aerobic glycolysis. To explore the potential role of Drosophila LDH in promoting biosynthesis, we examined how Ldh mutations influence larval development. Our studies unexpectedly found that Ldh mutants grow at a normal rate, indicating that LDH is dispensable for larval biomass production. However, subsequent metabolomic analyses suggested that Ldh mutants compensate for the inability to produce lactate by generating excess glycerol-3-phosphate (G3P), the production of which also influences larval redox balance. Consistent with this possibility, larvae lacking both LDH and G3P dehydrogenase (GPDH1) exhibit growth defects, synthetic lethality and decreased glycolytic flux. Considering that human cells also generate G3P upon inhibition of lactate dehydrogenase A (LDHA), our findings hint at a conserved mechanism in which the coordinate regulation of lactate and G3P synthesis imparts metabolic robustness to growing animal tissues.

Two signal half-century: From negative selection of self-reactivity to positive selection of near-self-reactivity

With the emergence of clonal selection ideas in the 1950s, the development of immune cell repertoires was seen to require the negative selection of self-reacting cells, with surviving cells exhibiting a broad range of specificities. Thus, confronting a universe of not-self-antigens, a potential host organism spread its resources widely. In the 1960s, the two signal hypothesis showed how this might work. However, in the 1970s an affinity/avidity model further proposed that anticipating a pathogen strategy of exploiting "holes" in the repertoire created by negative selection, hosts should also positively select near-self-reacting cells. A microbe mutating an antigen from a form foreign to its host to a form resembling that host should prevail over host defences with respect to that antigen. By mutating a step towards host self, along the path from non-self to self, it should come to dominate the microbe population. By progressive stepwise mutations, such microbes would become better adapted, to the detriment of their hosts. But they would lose this advantage if, as they mutated closer to host self, they encountered progressively stiffer host defences. Thus, as described in the affinity/avidity model, positive selection of lymphocytes for specificities that were very close to, but not quite, anti-self (ie, "anti-near-self") should be an important host adaptation. While positive selection affects both B and T cells, mechanisms are uncertain. Converging evidence from studies of lymphocyte activation, either polyclonally (with lectins as "antigen-analogs") or monoclonally (by specific antigen), supports the original generic affinity/avidity model for countering mutations towards host self.

Immunometabolism in rheumatoid arthritis

Recent studies have revealed a relationship between cellular metabolism and cell function in immune cells. Cellular metabolism not only provides supplemental ATP, but also supports dynamic changes in cell proliferation and differentiation. For example, T cells exhibit subset-specific metabolic profiles, and require certain types of metabolism for their functions. Determining the metabolic profiles that support inflammatory immune responses may lead to novel treatment strategies for chronic inflammatory diseases such as rheumatoid arthritis (RA). However, the mechanisms by which metabolism modulates cell function have been unclear. Recent studies have begun to unveil unexpected non-metabolic functions for metabolic enzymes in the context of inflammation, including roles in signaling and gene regulation. Here we describe recent findings related to immunometabolism, the metabolome of RA patients, and the metabolically independent functions of glycolytic enzymes. We discuss how metabolic processes impact immune cells, especially T cells and fibroblast like synoviocytes, which are considered the orchestrators of autoimmune arthritis.

Immunometabolic Regulation of Interleukin-17-Producing T Helper Cells: Uncoupling New Targets for Autoimmunity

Interleukin-17-producing T helper (Th17) cells are critical for the host defense of bacterial and fungal pathogens and also play a major role in driving pathogenic autoimmune responses. Recent studies have indicated that the generation of Th17 cells from naïve CD4⁺ T cells is coupled with massive cellular metabolic adaptations, necessary to cope with different energy and metabolite requirements associated with switching from a resting to proliferative state. Furthermore, Th17 cells have to secure these metabolic adaptations when facing nutrient-limiting environments, such as at the sites of inflammation. Accumulating data indicates that this metabolic reprogramming is significantly linked to the differentiation of T helper cells and, particularly, that the metabolic changes of Th17 cells and anti-inflammatory Forkhead box P3⁺ regulatory T cells are tightly and reciprocally regulated. Thus, a better understanding of these processes could offer potential new targets for therapeutic interventions for autoimmune diseases. In this mini-review, we will highlight some of the recent advances and discoveries in the field, with a particular focus on metabolic demands of Th17 cells and their implications for autoimmunity.

Cellular metabolism on T-cell development and function

Cell metabolism is closely related to the host immunity in many respects. We herein briefly summarized the recent progress on the roles of cellular metabolism in T-cell development, homeostasis, differentiation and functions. Relatively quiescent naïve T cells only require energy for survival and migration, and they mainly metabolize glucose to carbon dioxide through oxidative phosphorylation. However, activated T cells engage in robust cell proliferation, produce of a range of effector molecules and migrate through peripheral tissues, so they utilizes glycolysis to convert glucose to lactate (termed aerobic glycolysis) to meet the significantly increased metabolic demands. Importantly, the differentiation of T-cell subsets and memory T cells (Tm) was also significantly shaped by distinct cellular metabolic pathways including glucose, amino acids (AA), fatty acids (FA), and others. Understanding the regulatory metabolic networks on immunity may offer new insights into the immune-related disorders and open novel potential therapies to prevent and treat immune diseases.

Distinct metabolic programs in activated T cells: opportunities for selective immunomodulation

For several decades, it has been known that T-cell activation in vitro leads to increased glycolytic metabolism that fuels proliferation and effector function. Recently, this simple model has been complicated by the observation that different T-cell subsets differentially regulate fundamental metabolic pathways under the control of distinct molecular regulators. Although the majority of these data have been generated in vitro, several recent studies have documented the metabolism of T cells activated in vivo. Here, we review the recent data surrounding the differential regulation of metabolism by distinct T-cell subsets in vitro and in vivo and discuss how differential metabolic regulation might facilitate T-cell function vis-à-vis proliferation, survival, and energy production. We further discuss the important therapeutic implications of differential metabolism across T-cell subsets and review recent successes in exploiting lymphocyte metabolism to treat immune-mediated diseases.

Small molecule inhibition of 6-phosphofructo-2-kinase suppresses t cell activation

Background

T cell activation is associated with a rapid increase in intracellular fructose-2,6-bisphosphate (F2,6BP), an allosteric activator of the glycolytic enzyme, 6-phosphofructo-1-kinase. The steady state concentration of F2,6BP in T cells is dependent on the expression of the bifunctional 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (PFKFB1-4) and the fructose-2,6-bisphosphatase, TIGAR. Of the PFKFB family of enzymes, PFKFB3 has the highest kinase:bisphosphatase ratio and has been demonstrated to be required for T cell proliferation. A small molecule antagonist of PFKFB3, 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3PO), recently has been shown to reduce F2,6BP synthesis, glucose uptake and proliferation in transformed cells. We hypothesized that the induction of PFKFB3 expression may be required for the stimulation of glycolysis in T cells and that exposure to the PFKFB3 antagonist, 3PO, would suppress T cell activation.

Methods

We examined PFKFB1-4 and TIGAR expression and F2,6BP concentration in purified CD3⁺ T cells stimulated with microbead-conjugated agonist antibodies specific for CD3 and the co-stimulatory receptor, CD28. We then determined the effect of 3PO on anti-CD3/anti-CD28-induced T cell activation, F2,6BP synthesis, 2-[1-¹⁴C]-deoxy-d-glucose uptake, lactate secretion, TNF-α secretion and proliferation. Finally, we examined the effect of 3PO administration on the development of delayed type hypersensitivity to methylated BSA and on imiquimod-induced psoriasis in mice.

Results

We found that purified human CD3⁺ T cells express PFKFB2, PFKFB3, PFKFB4 and TIGAR, and that anti-CD3/anti-CD28 conjugated microbeads stimulated a >20-fold increase in F2,6BP with a coincident increase in protein expression of the PFKFB3 family member and a decrease in TIGAR protein expression. We then found that exposure to the PFKFB3 small molecule antagonist, 3PO (1–10 μM), markedly attenuated the stimulation of F2,6BP synthesis, 2-[1-¹⁴C]-deoxy-D-glucose uptake, lactate secretion, TNF-α secretion and T cell aggregation and proliferation. We examined the in vivo effect of 3PO on the development of delayed type hypersensitivity to methylated BSA and on imiquimod-induced psoriasis in mice and found that 3PO suppressed the development of both T cell-dependent models of immunity in vivo.

Conclusions

Our data demonstrate that inhibition of the PFKFB3 kinase activity attenuates the activation of T cells in vitro and suppresses T cell dependent immunity in vivo and indicate that small molecule antagonists of PFKFB3 may prove effective as T cell immunosuppressive agents.

Induction of glucose metabolism in stimulated T lymphocytes is regulated by mitogen-activated protein kinase signaling

T lymphocytes play a critical role in cell-mediated immune responses. During activation, extracellular and intracellular signals alter T cell metabolism in order to meet the energetic and biosynthetic needs of a proliferating, active cell, but control of these phenomena is not well defined. Previous studies have demonstrated that signaling from the costimulatory receptor CD28 enhances glucose utilization via the phosphatidylinositol-3-kinase (PI3K) pathway. However, since CD28 ligation alone does not induce glucose metabolism in resting T cells, contributions from T cell receptor-initiated signaling pathways must also be important. We therefore investigated the role of mitogen-activated protein kinase (MAPK) signaling in the regulation of mouse T cell glucose metabolism. T cell stimulation strongly induces glucose uptake and glycolysis, both of which are severely impaired by inhibition of extracellular signal-regulated kinase (ERK), whereas p38 inhibition had a much smaller effect. Activation also induced hexokinase activity and expression in T cells, and both were similarly dependent on ERK signaling. Thus, the ERK signaling pathway cooperates with PI3K to induce glucose utilization in activated T cells, with hexokinase serving as a potential point for coordinated regulation.

The metabolic life and times of a T-cell

SUMMARY

The regulation of lymphocyte homeostasis is critical for the development and formation of productive immune responses. Cell numbers must be maintained to allow sufficient numbers of lymphocytes to combat foreign pathogens but prevent the accumulation of excess lymphocytes that may increase the risk of developing autoimmunity or neoplasia. Cell extrinsic growth factors are essential to maintain homeostasis and cell survival, and it has become increasingly apparent that a key mechanism of this control is through regulation of cell metabolism. The metabolic state of T cells can have profound influences on cell growth and survival and even differentiation. In particular, resting T cells utilize an energy efficient oxidative metabolism but shift to a highly glycolytic metabolism when stimulated to grow and proliferate by pathogen encounter. After antigen clearance, T cells must return to a more quiescent oxidative metabolism to support T-cell memory. This review highlights how these metabolic changes may be intricately involved with both T-cell growth and death in the control of homeostasis and immunity.

Mycoplasma inhibition of phytohemagglutinin stimulation of lymphocytes

Goat lymphocytes were cultured in vitro with phytohemagglutinin and nonviable mycoplasmas. Addition of the mycoplasmas, even as late as 45 hours after adding phytohemagglutinin, completely inhibited the increase in synthesis of DNA and RNA normally induced in lymphocytes by the mitogen. The suppression of synthesis did not result from killing of the cells by the mycoplasmas, combination of the organisms with phytohemagglutinin, or competition for combining sites on the cell surface, which indicates that some other mechanism of inhibition was operative. A similar depression of response to phytohemagglutinin in lymphocytes in culture has been observed in human diseases associated with an immune defect. The present demonstration that at least certain mycoplasmas can profoundly affect lymphocyte function in vitro suggests that thay may alter the immune response in vivo.

Glutamine metabolism is essential for human cytomegalovirus infection

Human fibroblasts infected with human cytomegalovirus (HCMV) were more viable than uninfected cells during glucose starvation, suggesting that an alternate carbon source was used. We have determined that infected cells require glutamine for ATP production, whereas uninfected cells do not. This suggested that during infection, glutamine is used to fill the tricarboxylic acid (TCA) cycle (anaplerosis). In agreement with this, levels of glutamine uptake and ammonia production increased in infected cells, as did the activities of glutaminase and glutamate dehydrogenase, the enzymes needed to convert glutamine to alpha-ketoglutarate to enter the TCA cycle. Infected cells starved for glutamine beginning 24 h postinfection failed to produce infectious virions. Both ATP and viral production could be rescued in glutamine-starved cells by the TCA intermediates alpha-ketoglutarate, oxaloacetate, and pyruvate, confirming that in infected cells, a program allowing glutamine to be used anaplerotically is induced. Thus, HCMV infection activates the mechanisms needed to switch the anaplerotic substrate from glucose to glutamine to accommodate the biosynthetic and energetic needs of the viral infection and to allow glucose to be used biosynthetically.

Feeding our immune system: impact on metabolism

Endogenous intestinal microflora and environmental factors, such as diet, play a central role in immune homeostasis and reactivity. In addition, microflora and diet both influence body weight and insulin-resistance, notably through an action on adipose cells. Moreover, it is known since a long time that any disturbance in metabolism, like obesity, is associated with immune alteration, for example, inflammation. The purpose of this review is to provide an update on how nutrients-derived factors (mostly focusing on fatty acids and glucose) impact the innate and acquired immune systems, including the gut immune system and its associated bacterial flora. We will try to show the reader how the highly energy-demanding immune cells use glucose as a main source of fuel in a way similar to that of insulin-responsive adipose tissue and how Toll-like receptors (TLRs) of the innate immune system, which are found on immune cells, intestinal cells, and adipocytes, are presently viewed as essential actors in the complex balance ensuring bodily immune and metabolic health. Understanding more about these links will surely help to study and understand in a more fundamental way the common observation that eating healthy will keep you and your immune system healthy.

Beyond aerobic glycolysis: transformed cells can engage in glutamine metabolism that exceeds the requirement for protein and nucleotide synthesis

Tumor cell proliferation requires rapid synthesis of macromolecules including lipids, proteins, and nucleotides. Many tumor cells exhibit rapid glucose consumption, with most of the glucose-derived carbon being secreted as lactate despite abundant oxygen availability (the Warburg effect). Here, we used 13C NMR spectroscopy to examine the metabolism of glioblastoma cells exhibiting aerobic glycolysis. In these cells, the tricarboxylic acid (TCA) cycle was active but was characterized by an efflux of substrates for use in biosynthetic pathways, particularly fatty acid synthesis. The success of this synthetic activity depends on activation of pathways to generate reductive power (NADPH) and to restore oxaloacetate for continued TCA cycle function (anaplerosis). Surprisingly, both these needs were met by a high rate of glutamine metabolism. First, conversion of glutamine to lactate (glutaminolysis) was rapid enough to produce sufficient NADPH to support fatty acid synthesis. Second, despite substantial mitochondrial pyruvate metabolism, pyruvate carboxylation was suppressed, and anaplerotic oxaloacetate was derived from glutamine. Glutamine catabolism was accompanied by secretion of alanine and ammonia, such that most of the amino groups from glutamine were lost from the cell rather than incorporated into other molecules. These data demonstrate that transformed cells exhibit a high rate of glutamine consumption that cannot be explained by the nitrogen demand imposed by nucleotide synthesis or maintenance of nonessential amino acid pools. Rather, glutamine metabolism provides a carbon source that facilitates the cell's ability to use glucose-derived carbon and TCA cycle intermediates as biosynthetic precursors.

Increased Fructose 2,6-bisphosphate in peripheral blood mononuclear cells of patients with diabetes

Fructose 2,6-bisphosphate (F2,6BP) is a powerful allosteric activator of 6-phosphofructo-1-kinase, which is the rate-limiting enzyme for glycolysis. Mitogenic stimulation of lymphocytes is related to an enhanced rate of glucose utilization and F2,6BP mediated activation of glycolysis. To determine the effect of hyperglycemia on intracellular glycolysis of lymphocytes, we measured intracellular F2,6BP content in peripheral blood mononuclear cells obtained from patients with diabetes and normal subjects. A total of 62 subjects participated in the present study. Venous blood samples were collected and peripheral blood mononuclear cells were separated by Ficoll gradients. Intracellular F2,6BP levels in peripheral blood mononuclear cells from normal control subjects were significantly lower than age-matched diabetic subjects. We observed a significant positive correlation between intracellular F2,6BP levels and long term glycemic control, as assessed by HbA1c. These data suggest that hyperglycemia increases intracellular F2,6BP in immune cells. These findings may help to clarify the impaired function in immune cells in patients with diabetes.

Isolated receptor binding domains of HTLV-1 and HTLV-2 envelopes bind Glut-1 on activated CD4+ and CD8+ T cells

BACKGROUND

We previously identified the glucose transporter Glut-1, a member of the multimembrane-spanning facilitative nutrient transporter family, as a receptor for both HTLV-1 and HTLV-2. However, a recent report concluded that Glut-1 cannot serve as a receptor for HTLV-1 on CD4 T cells: This was based mainly on their inability to detect Glut-1 on this lymphocyte subset using the commercial antibody mAb1418. It was therefore of significant interest to thoroughly assess Glut-1 expression on CD4 and CD8 T cells, and its association with HTLV-1 and -2 envelope binding.

RESULTS

As previously reported, ectopic expression of Glut-1 but not Glut-3 resulted in significantly augmented binding of tagged proteins harboring the receptor binding domains of either HTLV-1 or HTLV-2 envelope glycoproteins (H1RBD or H2RBD). Using antibodies raised against the carboxy-terminal peptide of Glut-1, we found that Glut-1 expression was significantly increased in both CD4 and CD8 cells following TCR stimulation. Corresponding increases in the binding of H1RBD as well as H2RBD, not detected on quiescent T cells, were observed following TCR engagement. Furthermore, increased Glut-1 expression was accompanied by a massive augmentation in glucose uptake in TCR-stimulated CD4 and CD8 lymphocytes. Finally, we determined that the apparent contradictory results obtained by Takenouchi et al were due to their monitoring of Glut-1 with a mAb that does not bind cells expressing endogenous Glut-1, including human erythrocytes that harbor 300,000 copies per cell.

CONCLUSION

Transfection of Glut-1 directly correlates with the capacities of HTLV-1 and HTLV-2 envelope-derived ligands to bind cells. Moreover, Glut-1 is induced by TCR engagement, resulting in massive increases in glucose uptake and binding of HTLV-1 and -2 envelopes to both CD4 and CD8 T lymphocytes. Therefore, Glut-1 is a primary binding receptor for HTLV-1 and HTLV-2 envelopes on activated CD4 as well as CD8 lymphocytes.

Phosphatidylinositol 3-kinase-dependent modulation of carnitine palmitoyltransferase 1A expression regulates lipid metabolism during hematopoietic cell growth

An abundant supply of extracellular nutrients is believed to be sufficient to suppress catabolism of cellular macromolecules. Here we show that, despite abundant extracellular nutrients, interleukin-3-deprived hematopoietic cells begin to catabolize intracellular lipids. Constitutive Akt activation blunts the increased beta-oxidation that accompanies growth factor withdrawal, and in growth factor-replete cells, phosphatidylinositol 3-kinase (PI3K) signaling is required to suppress lipid catabolism. Surprisingly, PI3K and Akt exert these effects by suppressing expression of the beta-oxidation enzyme carnitine palmitoyltransferase 1A (CPT1A). Cells expressing a short hairpin RNA against CPT1A fail to induce beta-oxidation in response to growth factor withdrawal and are unable to survive glucose deprivation. When CPT1A is constitutively expressed, growth factor stimulation fails to repress beta-oxidation. As a result, both net lipid synthesis and cell proliferation are diminished. Together, these results demonstrate that modulation of CPT1A expression by PI3K-dependent signaling is the major mechanism by which cells suppress beta-oxidation during anabolic growth.

IL-7-induced proliferation of recent thymic emigrants requires activation of the PI3K pathway

The IL-7 cytokine promotes the survival of a diverse T-cell pool, thereby ensuring an efficient immune response. Moreover, IL-7 induces the proliferation of recent thymic emigrants (RTEs) in neonates. Here, we demonstrate that the survival and proliferative effects of IL-7 on human RTEs can be distinguished on the basis of dose as well as duration of IL-7 administration. A dose of 0.1 ng/mL IL-7 is sufficient to promote viability, whereas cell-cycle entry is observed only at doses higher than 1 ng/mL. Moreover, a short 1-hour exposure to high-dose IL-7 (10 ng/mL) induces long-term survival but continuous IL-7 exposure is necessary for optimal cell-cycle entry and proliferation. We find that distinct signaling intermediates are activated under conditions of IL-7-induced survival and proliferation; STAT5 tyrosine phosphorylation does not correlate with proliferation, whereas up-regulation of the glucose transporter Glut-1 as well as increased glucose uptake are markers of IL-7-induced cell cycle entry. Glut-1 is directly regulated by PI3K and, indeed, inhibiting PI3K activity abrogates IL-7-induced proliferation. Our finding that the survival and proliferation of RTEs are differentially modulated by the dose and kinetics of exogenous IL-7 has important implications for the clinical use of this cytokine.

Antigen receptor-mediated changes in glucose metabolism in B lymphocytes: role of phosphatidylinositol 3-kinase signaling in the glycolytic control of growth

The bioenergetic response of B lymphocytes is subject to rapid changes following antigen encounter in order to provide ATP and anabolic precursors necessary to support growth. However, the pathways involved in glucose acquisition and metabolism are unknown. We find that B lymphocytes rapidly increase glucose uptake and glycolysis following B-cell antigen receptor (BCR) crosslinking. Inhibition of glycolysis blocks BCR-mediated growth. Prior to S-phase entry, glucose metabolism shifts from primarily glycolytic to include the pentose phosphate pathway. BCR-induced glucose utilization is dependent upon phosphatidylinositol 3-kinase (PI-3K) activity as evidenced by inhibition of glucose uptake and glycolysis with LY294002 treatment of normal B cells and impaired glucose utilization in B cells deficient in the PI-3K regulatory subunit p85alpha. Activation of Akt is sufficient to increase glucose utilization in B cells. We find that glucose utilization is inhibited by coengagement of the BCR and FcgammaRIIB, suggesting that limiting glucose metabolism may represent an important mechanism underlying FcgammaRIIB-mediated growth arrest. Taken together, these findings demonstrate that both growth-promoting BCR signaling and growth-inhibitory FcgammaRIIB signaling modulate glucose energy metabolism. Manipulation of these pathways may prove to be useful in the treatment of lymphoproliferative disorders, wherein clonal expansion of B lymphocytes plays a role.

Glucose transporter 1 expression identifies a population of cycling CD4+ CD8+ human thymocytes with high CXCR4-induced chemotaxis

GLUT1, the major glucose transporter in peripheral T lymphocytes, is induced upon T cell receptor activation. However, the role of GLUT1 during human thymocyte differentiation remains to be evaluated. Our identification of GLUT1 as the human T lymphotrophic virus (HTLV) receptor has enabled us to use tagged HTLV-receptor-binding domain fusion proteins to specifically monitor surface GLUT1 expression. Here, we identify a unique subset of CD4+ CD8+ double-positive (DP) thymocytes, based on their GLUT1 surface expression. Whereas these cells express variable levels of CD8, they express uniformly high levels of CD4. Glucose uptake was 7-fold higher in CD4(hi) DP thymocytes than in CD4(lo) DP thymocytes (P = 0.0002). Further analyses indicated that these GLUT1+ thymocytes are early post-beta-selection, as demonstrated by low levels of T cell receptor (TCR)alphabeta and CD3. This population of immature GLUT1+ DP cells is rapidly cycling and can be further distinguished by specific expression of the transferrin receptor. Importantly, the CXCR4 chemokine receptor is expressed at 15-fold higher levels on GLUT1+ DP thymocytes, as compared with the DP GLUT1- subset, and the former cells show enhanced chemotaxis to the CXCR4 ligand CXCL12. Thus, during human thymopoiesis, GLUT1 is up-regulated after beta-selection, and these immature DP cells constitute a population with distinct metabolic and chemotactic properties.

Cytokine stimulation of aerobic glycolysis in hematopoietic cells exceeds proliferative demand

The relationship between growth factor-dependent cell growth and proliferation and the up-regulation of cellular metabolism required to support these processes remains poorly defined. Here, we demonstrate that cell growth, proliferation, and glucose metabolism are coordinately regulated by interleukin-3 (IL-3) in cytokine-dependent cells. Surprisingly, glycolytic activity is stimulated to a greater extent than would be expected based on the rate of cell growth or proliferation. IL-3 signaling exerts a direct effect on glycolytic commitment independent of cell growth control. These results are not restricted to IL-3 as the cytokines IL-7 and IL-2 have similar effects on glucose metabolism when assayed in factor-dependent cell lines or primary lymphocytes, respectively. Growth factor stimulation leads cells to consume less oxygen and produce more lactate per glucose, indicative of conversion from oxidative to glycolytic metabolism. The enforced rate of glucose metabolism is in excess of that required to support cell growth; accordingly, if extracellular glucose is reduced, cells retain the ability to grow and proliferate by derepressing oxidative metabolism. These data suggest that the high rate of glycolysis observed in response to growth factor stimulation is a primary effect rather than a homeostatic response to increased cell growth.

Low proliferation capacity of lymphocytes from alloxan-diabetic rats: involvement of high glucose and tyrosine phosphorylation of Shc and IRS-1

The proliferation capacity of lymphocytes obtained from mesenteric lymph nodes of control and alloxan-diabetic (40 mg/kg) rats in response to concanavalin A (ConA) and lipopolysaccharide (LPS) stimuli was examined. Proliferation response of lymphocytes from diabetic rats was significantly reduced under Con A (43%) and LPS (46%) stimulation as compared with the control group. Insulin (166 microM) promoted a marked increase of lymphocyte proliferation (7.5-fold) in the control group and this response was much lower (2.6-fold) in lymphocyte from diabetic rats. Cells were also cultured in medium containing glucose at 5, 10 or 20 mM. High glucose concentration (20 mM) caused a marked inhibition of lymphocyte proliferation reaching the values of the diabetic group. In lymphocytes from control rats, the degree of Shc tyrosine phosphorylation was gradually increased, whereas that of cells from diabetic rats was much lower in response to insulin. In lymphocytes obtained from control rats, the tyrosine phosphorylation of IRS-1 was time-dependent on insulin. In cells from diabetic rats, the basal tyrosine phosphorylation of IRS-1 was higher than that of control rats, however, there was no further phosphorylation after insulin addition. We conclude that the response of lymphocyte proliferation from diabetic rats to Con A and LPS stimuli is decreased but insulin was able to promote a significant proliferative effect on these cells. Also, high glycemia in addition to the lack of insulin participates in the reduced proliferation capacity of lymphocytes from diabetic rats.

The CD28 signaling pathway regulates glucose metabolism

Lymphocyte activation initiates a program of cell growth, proliferation, and differentiation that increases metabolic demand. Although T cells increase glucose uptake and glycolysis during an immune response, the signaling pathways that regulate these increases remain largely unknown. Here we show that CD28 costimulation, acting through phosphatidylinositol 3'-kinase (PI3K) and Akt, is required for T cells to increase their glycolytic rate in response to activation. Furthermore, CD28 controls a primary response pathway, inducing a level of glucose uptake and glycolysis in excess of that needed to maintain cellular ATP/ADP levels or macromolecular synthesis. These data suggest that CD28 costimulation functions to increase glycolytic flux, allowing T cells to anticipate energetic and biosynthetic needs associated with a sustained response.

THE STIMULATION OF DNA SYNTHESIS IN CULTURES OF RABBIT LYMPH NODE AND SPLEEN CELL SUSPENSIONS BY HOMOLOGOUS CELLS

An early proliferative response follows the mixing of homologous spleen or lymph node suspensions obtained from two unrelated rabbits. The rate of incorporation of radioactive thymidine has been used as a quantitative measure of this response. Thymus cells do not respond to homologous cell suspensions but may on occasion serve to stimulate the response in homologous spleen or lymph node cells. Homologous erythrocytes or autologous tissues do not stimulate a response. No response occurs if the two cell populations are separated by a Millipore membrane. Autoradiographic studies have established that 1 to 2 per cent of the intial cell population is involved in the response and they are large undifferentiated cells by the time they can first be identified as responders. There was no morphological evidence of any cellular interaction and the viability of mixed suspensions was not measurably different from that observed in separate suspension. Simultaneous additive responses could be obtained to homologous cells and to antigen when cell suspensions from immunized rabbits were used. The interaction of the cell populations from the two rabbits did not appear to suppress the response of each to antigen. The speed and magnitude of the response were in everyway comparable with the secondary response of cell suspensions from immunized rabbits exposed to the immunizing antigen. No evidence was obtained of any enhancement of the response to homologous cells by prior immunization with homologous tissues, but the possibility that it had occurred was not rigidly excluded.

Cytokine production after helium-neon laser irradiation in cultures of human peripheral blood mononuclear cells

The effects of laser light on the immune system have not been extensively characterized. Low-power laser sources, such as the helium-neon (He-Ne) laser with a wavelength of 632.8 nm, have been found to produce photobiological effects with evidence of interference with immunological functions. We have investigated the effects of He-Ne laser irradiation on Ficoll-Hypaque-isolated human peripheral blood mononuclear cells (PBMC). Cultured cells were irradiated for various times at two selected intensities and then stimulated with different mitogens. The rate of incorporation of 3H-thymidine into the DNA of stimulated cells decreased with increasing energy density. The levels of interleukin-1 alpha (IL-1 alpha), interleukin-2 (IL-2), tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma) in supernatants of the cultures were determined (irradiated either before or after stimulation). When stimulating cells after irradiation, significantly increased levels of all cytokines were detected after 30 min of irradiation (18.9 J cm-2), whereas after 60 min of irradiation (37.8 J cm-2) cytokine levels were found to be significantly decreased.

Culture kinetics of glycolytic enzyme induction, glucose utilization, and thymidine incorporation of extended-exposure phytohemagglutinin-stimulated human lymphocytes

Glycolytic enzyme activity is significantly (P less than 0.05) induced between 24 and 48 hours of incubation in phytohemagglutinin-stimulated human lymphocytes. Nonstimulated cultured cells do not show this induction although these cells have an approximate daily doubling of thymidine incorporation. Maximal glycolytic enzyme activity is reached between 96 and 120 hours of culture in stimulated cells (3.5-fold increase) and maintained until at least 168 hours. There is no significant induction of the hexosemonophosphate shunt or the TCA cycle during seven-day transformation. Induction of glucose utilization becomes significantly (P less than 0.05) greater in stimulated as compared to nonstimulated cultures between 48 and 72 hours of culture and is significantly elevated for at least an additional 96 hours. There is a 17% increase in total protein in the stimulated cells after 24 hours of culture and higher levels of protein content are then maintained over the control. Thymidine incorporation is significantly greater in stimulated cells from 24-144 hours of culture but is not significantly different from the nonstimulated cells at 168 hours (P = 0.98) although glycolytic enzyme activity remains elevated in the stimulated cells. There is a greater enzyme induction of the latter phase of glycolysis during transformation and this phenomenon continues in extended cultures. Increases in glycolytic enzyme activity during mitogenesis appear to be an intrinsic phenomenon independent of cell proliferation and glucose transport. The mitogen-induced increase in the activity of the glycolytic enzymes accompanies blastogenesis and the sustained elevated activity of these enzymes to be related to the high metabolic rate of transformed cells.

Maximum activities of some enzymes of glycolysis, the tricarboxylic acid cycle and ketone-body and glutamine utilization pathways in lymphocytes of the rat

1. The maximum activity of hexokinase in lymphocytes is similar to that of 6-phosphofructokinase, but considerably greater than that of phosphorylase, suggesting that glucose rather than glycogen is the major carbohydrate fuel for these cells. Starvation increased slightly the activities of some of the glycolytic enzymes. A local immunological challenge in vivo (a graft-versus-host reaction) increased the activities of hexokinase, 6-phosphofructokinase, pyruvate kinase and lactate dehydrogenase, confirming the importance of the glycolytic pathway in cell division. 2. The activities of the ketone-body-utilizing enzymes were lower than those of hexokinase or 6-phosphofructokinase, unlike in muscle and brain, and were not affected by starvation. It is suggested that the ketone bodies will not provide a quantitatively important alternative fuel to glucose in lymphocytes. 3. Of the enzymes of the tricarboxylic acid cycle whose activities were measured, that of oxoglutarate dehydrogenase was the lowest, yet its activity (about 4.0mumol/min per g dry wt. at 37 degrees C) was considerably greater than the flux through the cycle (0.5mumol/min per g calculated from oxygen consumption by incubated lymphocytes). The activity was decreased by starvation, but that of citrate synthase was increased by the local immunological challenge in vivo. It is suggested that the rate of the cycle would increase towards the capacity indicated by oxoglutarate dehydrogenase in proliferating lymphocytes. 4. Enzymes possibly involved in the pathway of glutamine oxidation were measured in lymphocytes, which suggests that an aminotransferase reaction(s) (probably aspartate aminotransferase) is important in the conversion of glutamate into oxoglutarate rather than glutamate dehydrogenase, and that the maximum activity of glutaminase is markedly in excess of the rate of glutamine utilization by incubated lymphocytes. The activity of glutaminase is increased by both starvation and the local immunological challenge in vivo. This last finding suggests that metabolism of glutamine via glutaminase is important in proliferating lymphocytes.

The relationship between lymphocyte nuclear morphology and cell cycle stage in lymphoid neoplasia

A significant percentage of lymphoid cells isolated from three lymphoid neoplasms (nodular lymphoma mixed cell type, mycosis fungoides, and Sézary syndrome) had tetraploid or near-tetraploid DNA content, as determined by flow cytometric analysis. In each case, a morphologically distinct population of cells with large, irregular nuclei was present, the percentage of which corresponded to the percentage of tetraploid cells. In a fourth case (diffuse "histiocytic" lymphoma), cells were sorted on the basis of DNA content from the G0-G1 compartment and compared morphologically to cells sorted from the S-G2(M) compartment. The G0-G1 cells has clumped nuclear chromatin, lacked prominent nucleoli, and had a mean nuclear diameter of 10.18 +/- 1.22 micrometer. The sorted cells with S-G2 (M) DNA content had one to several prominent nucleoli and less clumped nuclear chromatin, and they were significantly larger, with a mean nuclear diameter of 13.76 +/- 1.59 micrometer (p less than 0.00001). These preliminary results suggest that, in lymphoid malignancies, certain morphologic characteristics of individual lymphoid cells are related to their DNA content (level of ploidy) and/or the stage of the cell within its division cycle.

Lectin-induced giant cell formation in the chicken wattle

The fusion of mononuclear cells has been observed in inflammatory reactions and in cell culture experiments. This report describes the in vivo fusion of macrophages and their cytological structures. Thick (1 micrometer) and thin sections of wattle were prepared 6, 12, 24, 48, and 96 hr after a single subcutaneous-wattle injection of phytohemagglutinin (PHA-P; .1 ml; 100 microgram) in saline. The injection of PHA-P induced withn 6 hr a blood borne mononuclear cell infiltration of the chicken's wattle. Giant cells (3 to 8 mononuclear cells) were found by 24 hr, reached a maximum number by 48 hr and declined perceptibly by 96 hr. After 48 hr the mononuclear cells possessed a well-developed Golgi apparatus, ergastroplasmic cisternae, and large amounts of glycogen-like granules which diminished by 96 hr. The influence of lectin on the glycogen content of macrophages is similar to published observatins on small lymphocytes and suggests a similar carbohydrate metabolism between these two cell types.

Changes in the activity and isozyme patterns of glycolytic enzymes during stimulation of normal human lymphocytes with phytohaemagglutinin

A study has been made of the effects of phytohaemagglutinin on the gene expression of the glycolytic enzymes in cultured human lymphocytes. All the enzymes were found to show an average increase in activity of between 160% and 360% in stimulated cells, but the increases were greater for the enzymes comprising the second half of the pathway. The enzyme activities in stimulated cells, cultured for 72 h, were similar to the activities measured in long-term lymphoid lines. Starch-gel electrophoresis was used to examine the isozyme patterns of the enzymes before and after exposure of the lymphocytes to PHA. Six of the enzymes showed isozyme patterns unchanged by stimulation. Four of the enzymes, aldolase, triosephosphate isomerase, enolase and lactate dehydrogenase, showed different isozyme patterns in stimulated cells from those seen in uncultured or unstimulated cells. The electrophoretic results showed a good correlation in isozyme pattern between uncultured lymphocytes and cultured unstimulated lymphocytes, and between PHA-stimulated lymphocytes and long-term lymphoid lines.

A new method of testing for mitogen-induced lymphocyte stimulation: measurement of the percentage of growing cells and of some aspects of their cell kinetics with an electronic particle counter

Human lymphocytes were cultured with or without added PHA for periods not exceeding one day so that none of the cells had entered the first mitotic division. The size distribution of the cells was measured with an electronic particle counter and the results were collected in a multichannel analyser. An iterative stochastic model was developed to estimate the proportion of responding cells and their growth characteristics. This mathematical model was based on a few simple assumptions about the pattern of cell growth and was considered to fulfill basic requirements of plausibility and parsimony. The technique described in this paper makes measurement of the absolute percentage of responding cells and their average growth rate in mitogen-induced lymphocyte stimulation tests possible in routine diagnostic laboratories for the first time.