Agents which block membrane lipid peroxidation enhance mouse spleen cell immune activities in vitro: relationship to the enhancing activity of 2-mercaptoethanol

Potential alteration of tumor microenvironments by β-mercaptoethanol

The therapeutic effectiveness of immune checkpoint inhibitors in cancer patients is quite profound. However, it is generally accepted that further progress is curtailed by accompanying adverse events and by low cure rates linked to the tumor microenvironment. The multitudes of immune processes altered by low-molecular-weight thiols published over the past decades suggest they have potential to alter tumor microenvironment processes which could result in an increase in immune checkpoint inhibitor survival rates. Based on one of the most studied and most potent low-molecular-weight thiols, β-mercaptoethanol (BME), it is proposed that clinical assessment be undertaken to identify any BME benefits with relevance for proliferation/differentiation of immune cells, lymphocyte exhaustion, immunogenicity of tumor antigens and inactivation of suppressor cells/factors. The BME alterations projected to be most effective are: maintenance/replacement of glutathione in lymphocytes via facilitation of cysteine uptake, inhibition of suppressor cells/soluble factors and inactivation of free-radical, reactive oxygen species.

A noticeable phenomenon: thiol terminal PEG enhances the immunogenicity of PEGylated emulsions injected intravenously or subcutaneously into rats

Repeated intravenous injection of long-circulating methoxy-polyethylene glycol (PEG)-liposomes alters the pharmacokinetics and biodistribution of the second administration, regarded as the "accelerated blood clearance (ABC) phenomenon." Nevertheless, the effect of terminal groups of distearoylphosphatidylethanolamine-polyethylene glycol (DSPE-PEG) on the induction of the ABC phenomenon had not been reported previously. In this study, rats were injected intravenously or subcutaneously with PEG coated emulsions (DE) which were prepared using PEG terminated with either the methoxyl (OCH3), hydroxyl (OH), amino (NH2), carboxyl (COOH), or thiol (SH) group. DE-OCH3 demonstrated the longest prolonged half-life in vivo after a single intravenous injection, followed by DE-SH and DE-COOH. In contrast, DE-OH was rapidly removed from the blood circulation, as was DE-NH2. Moreover, we observed a strong positive relationship between the circulation time of initially injected PEGylated emulsions and the extent to which the ABC phenomenon was induced, but a exception of DE-SH increasing the ABC effect. Furthermore, the present study suggested that thiols might stimulate the proliferation and differentiation of B cells to induce the fastest clearance of the second intravenous administration by inducing the synthesis of the cell membrane and cytosolic proteins or reacting with follicular dendritic cells. The results strongly suggested that thiol groups played a stimulatory role in the immune response and provided a considerable implication for multiple drug therapy of thiol groups.

Dietary polyunsaturated fatty acids modulate in vivo, antigen-driven CD4+ T-cell proliferation in mice

Our objective was to determine whether dietary lipids affect in vivo, antigen-driven, proliferation of naïve CD4(+) T lymphocytes. To accomplish this, we adoptively transferred lymphocytes from T-cell receptor (TCR) transgenic DO11.10 (i.e., donor) mice into syngeneic, nontransgenic BALB/c (i.e., recipient) mice. Before adoptive transfer, recipient mice were fed for 4 wk AIN93G-type diets that differed only in fat source: lard, low in PUFA, fish oil, rich in (n-3) PUFA, and soybean oil, rich in (n-6) PUFA. One week after transfer, recipient mice were immunized with antigen (i.e., ovalbumin), and expansion of CD4(+) T(DO11.10) cells in the spleen and draining lymph nodes (LN) was measured by flow cytometry. Five days postimmunization (p.i.), at the peak of expansion, CD4(+) T(DO11.10) cells in the draining LN and spleen were 5- to 10-fold higher than in unimmunized mice, then quickly declined during the contraction phase (i.e., 7 and 10 d p.i.). Recipients fed the (n-6) PUFA rich diet had approximately 25% greater in vivo expansion of CD4(+) T(DO11.10) cells than lard- and fish oil-fed recipient mice at 5 d p.i. (P < 0.05). However, at 7 and 10 d p.i., CD4(+) T(DO11.10) cells in the draining lymph nodes did not differ between groups, nor in the spleen at 5, 7, and 10 d p.i. In summary, we are the first to demonstrate that dietary PUFAs affect antigen-driven expansion of naïve CD4(+) T cells in vivo. Surprisingly, (n-3) PUFA consumption did not reduce CD4(+) T-cell expansion.

Antigen-driven murine CD4+ T lymphocyte proliferation and interleukin-2 production are diminished by dietary (n-3) polyunsaturated fatty acids

This study is the first to describe the impact of consuming a diet rich in (n-3) polyunsaturated fatty acids (PUFA) from fish oil on antigen-driven activation of naive CD4+ T lymphocytes. To accomplish this, we used lymphocytes isolated from T cell receptor (TCR) transgenic mice (i.e., DO11.10). A large portion of the T lymphocytes from these mice expresses a TCR specific for a peptide within the ovalbumin (OVA) molecule (OVA(323-339)). When this antigen is presented in the context of major histocompatibility complex I-A(d) with costimulation, these naive CD4+ T cells become activated, produce interleukin (IL)-2 and clonally expand. (n-3) PUFA enrichment was accomplished by feeding DO11.10 mice one of two nutritionally complete experimental diets that differed only in the source of fat: lard or menhaden fish oil [high in (n-3) PUFA]. After 2 wk of consuming the experimental diets, lymphocytes were isolated from the spleen of each mouse, then cultured in the presence of antigen (i.e., OVA(323-339)) or concanavalin A (Con A), a nonspecific, polyclonal T cell stimulus. IL-2 production and lymphocyte proliferation were determined after 48 and 72 h, respectively. Naive CD4+ T lymphocytes from fish oil-fed mice stimulated with antigen produced less IL-2 ( approximately 33%; P < 0.001) and proliferated to a lesser extent ( approximately 50%; P < 0.0001) than the same cells from lard-fed DO11.10 mice. When stimulated with Con A, (n-3) PUFA did not affect either proliferation or IL-2 production. In summary, we report for the first time that feeding mice a diet enriched with (n-3) PUFA reduces in vitro antigen-stimulated production of IL-2 and subsequent proliferation of naive CD4+ T lymphocytes.

Elevation of glutathione induced by low-dose gamma rays and its involvement in increased natural killer activity

We examined the relationship between the induction of an increase in the level of glutathione and the elevation of natural killer (NK) activity in mouse splenocytes by a low dose of gamma rays. The glutathione levels in mouse splenocytes increased significantly between 2 h and 6 h after whole-body gamma irradiation at 0.5 Gy, peaked at 4 h, and then decreased almost to the level before irradiation by 12 h postirradiation. A significant enhancement of NK activity was found in the splenocytes obtained from whole-body-irradiated mice between 4 and 6 h postirradiation. Reduced glutathione (GSH) added exogenously to splenocytes obtained from normal mice enhanced both the total cellular glutathione content and the NK activity in a dose-dependent manner. Other precursors of de novo GSH synthesis, such as cysteine, N-acetylcysteine and oxidized glutathione, also increased the activity. These enhancements were completely blocked by buthionine sulfoximine, an inhibitor of de novo GSH synthesis. We conclude that the induction of endogenous glutathione in living cells immediately after low-dose gamma irradiation is at least partially responsible for the appearance of enhanced NK activity.

Vitamin E supplementation improves cell-mediated immunity and oxidative stress of Asian men and women

Vitamin E is an efficient antioxidant and a modulator of the immune system. Although racial differences in both baseline vitamin E level and immunologic subsets are known, no reliable data exist for the Asian population. Furthermore, the extent of the effect of alpha-tocopherol in protecting lymphocyte cells against oxidative stress and its association with cell-mediated immunity have not been elucidated. This study was undertaken to investigate the immunologic and antioxidant effects of vitamin E in healthy ethnic Chinese men and women. Volunteers < 35 y old (n = 26) were supplemented with 233 mg/d dl-alpha-tocopherol for 28 d. The in vitro proliferative response to phytohemagglutinin (PHA) or lipopolysaccharide (LPS) of T-lymphocytes was determined in the study group before and after vitamin E supplementation. Cell-mediated immunity subsets and hydrogen peroxide production in T-lymphocytes were investigated by flow cytometry. The oxidant-antioxidant balance in plasma and urine was studied by spectrophotometric and gas chromatography-mass selective detection methods. The antioxidant properties of vitamin E were established (P: < 0.01) by the elevation of plasma vitamin E, together with depression in both plasma malondialdehyde and urinary DNA adduct 8-hydroxy-2'-deoxyguanosine after supplementation. Our data suggest a specific requirement for vitamin E in total-T and T-helper cell proliferation. We present the first evidence of the beneficial effects of supplemental vitamin E in healthy Chinese individuals on cell-mediated immunity and oxidative stress.

Abeta25-35 induces rapid lysis of red blood cells: contrast with Abeta1-42 and examination of underlying mechanisms

Amyloid beta-peptide (A beta) is produced by many different cell types and circulates in blood and cerebrospinal fluid in a soluble form. In Alzheimer's disease (AD), A beta forms insoluble fibrillar aggregates that accumulate in association with cells of the brain parenchyma and vasculature. Both full-length A beta (A beta1-40/42) and the A beta25-35 fragment can damage and kill neurons by a mechanism that may involve oxidative stress and disruption of calcium homeostasis. Circulating blood cells are exposed to soluble A beta1-40/42 and may also be exposed to A beta aggregates associated with the luminal surfaces of cerebral microvessels. We therefore examined the effects of A beta25-35 and A beta1-42 on human red blood cells (RBCs) and report that A beta25-35, in contrast to A beta1-42, induces rapid (10-60 min) lysis of RBCs. The mechanism of RBC lysis by A beta25-35 involved ion channel formation and calcium influx, but did not involve oxidative stress because antioxidants did not prevent cell lysis. In contrast, A beta1-42 induced a delayed (4-24 h) damage to RBCs which was attenuated by antioxidants. The damaging effects of both A beta25-35 and A beta1-42 towards RBCs were completely prevented by Congo red indicating a requirement for peptide fibril formation. A beta1-42 induced membrane lipid peroxidation in RBC, and basal levels of lipid peroxidation in RBCs from AD patients were significantly greater than in age-matched controls, suggesting a possible role for A beta1-42 in previously reported alterations in RBCs from AD patients.

Follicular dendritic cells and presentation of antigen and costimulatory signals to B cells

This review focuses on how immunogens trapped by FDC in the form of Ag-Ab complexes productively signal B cells. In vitro. Ag-Ab complexes are poorly immunogenic but in vivo immune complexes elicit potent recall responses. FDC trap Ag-Ab complexes and make immune complex coated bodies or "iccosomes". B cells endocytose iccosomes, the Ag is processed, and T-cell help is elicited. In vitro, addition of FDC bearing appropriate Ag-Ab complex to memory T and B cells provoke potent recall responses (IgG and IgE). FDC also provide nonspecific costimulatory signals which augment B-cell proliferation and Ab production. B cell-FDC contact is important and interference with ICAM-1-LFA-1 interactions reduces FDC-mediated costimulation. Preliminary data suggest that a costimulatory signal may be delivered via CR2L on FDC binding CR2 on B cells. FDC can also stimulate B cells to become chemotactically active and can protect lymphocytes from apoptosis. FDC also appear to be rich in thiol groups and may replace reducing compounds such as 2 mercaptoethanol in cultures. In short, FDC-Ag specifically signals B cells through BCR, and FDC provide B cells with iccosomal-Ag necessary for processing to elicit T-cell help. In addition, FDC provide nonspecific signals that are important to promote B-cell proliferation, maintain viability, and induce chemotactic responsiveness.

Down-regulation of canine airway mast cell function following exposure to ozone in vivo

The influence of ozone on the function of airway cells involved in allergic responses is of particular interest due to the increasing prevalence of this environmental oxidant pollutant. In the present studies, the peripheral airways of Ascaris-sensitive dogs were expose to ozone (1 ppm, 5 min) or air (control) and the exposed segments were lavaged 30 min later. The kinetics and magnitude of release of PGD2 and histamine from canine peripheral airway mast cells (PAMC) was determined following in vitro challenge with Ascaris antigen or calcium ionophore approximately 4 h from the time of the in vivo exposures. Histamine content was significantly lower in PAMC retrieved from ozone- versus air-exposed segments (3.0 +/- 0.1 vs. 5.2 +/- 0.5 pg/cell). Absolute release of histamine at 20 min was decreased by 47 and 43% in ozone-exposed cells stimulated with antigen or ionophore, respectively. Maximal synthesis and release of PGD2 in response to antigen (345 +/- 22 pg/10(3) PAMC) or ionophore (1055 +/- 104 pg/10(3) PAMC) was inhibited by 32 and 55%, respectively, in cells from ozone-exposed segments. Inhibition of prostanoid synthesis was not observed in alveolar macrophages in the lavage samples, nor could decreased PGD2 be attributed to enhanced catabolism. These data indicate a differential down-regulatory influence of ozone on subsequent release of granular mediators and newly synthesized PGD2 from PAMC following brief in vivo exposure that lasts for several hours.

Redox regulation of programmed cell death in lymphocytes

A redox imbalance caused by an over-production of prooxidants or a decrease in antioxidants seems to play a role in the programmed cell death that occurs in various developmental programs. Such a physiological function for oxidative stress is particularly applicable to the immune system, wherein individual lymphocytes undergo continuous scrutiny to determine if they should be preserved or programmed to die. Following activation, lymphocytes produced increased levels of reactive oxygen species (ROS) which may serve as intracellular signaling molecules. The ultimate outcome of this increased ROS formation, i.e., lymphocyte proliferation versus programmed cell death, may be dictated by macrophage-derived costimulatory molecules that bolster or diminish lymphocyte antioxidant defenses. HIV-1-infected individuals display multiple symptoms of redox imbalance consistent with their being in oxidative stress, and lymphocytes from such individuals are more prone to undergo apoptosis in vitro. It is suggested that oxidative stress, and lymphocytes from such individuals are more prone to undergo apoptosis in vitro. It is suggested that oxidative stress is a physiological mediator of programmed cell death in lymphoid cells, and that HIV disease represents an extreme case of what can happen when regulatory safeguards are compromised.

2-Mercaptoethanol influences the in vitro function of bovine peripheral blood mononuclear cells

The effects of 2-mercaptoethanol (2-ME) on some in vitro functions of bovine peripheral blood mononuclear cells (PBMC) were examined. It was shown that 2-ME enhanced, in a dose-dependent manner, the production of antibodies to bovine coronavirus. In this test the optimal concentration of 2-ME was 50 microM. This molarity of 2-ME was also optimal for the pokeweed mitogen (PWM)-induced proliferation of PBMC obtained from the 7 cattle tested. Similarly, the spontaneous proliferation of PBMC from 4 out of these cattle was enhanced. Thus, 2-ME evoked an increase (up to 2.5 times) or a decrease (at most 10 times) of the quota between the PWM-induced and the spontaneous proliferation (stimulation index). In general, the presence of 50 microM 2-ME enhanced the in vitro production of interferon by bovine PBMC. On the contrary, the highest proliferative response of PBMC to stimulation with bovine virus diarrhoea virus was achieved in cultures without 2-ME or in cultures with 0.5 or 5 microM 2-ME. Since the effects of 2-ME varied, for different tests as well as for cattle tested, attention should be paid to the use of 2-ME in cultures of bovine PBMC.

Suppressive effect of hyperbaric oxygenation on immune responses of normal and autoimmune mice

We studied the effect of hyperbaric oxygenation (HBO) on immune responses in normal and autoimmune mice. Mice were exposed to HBO in an animal chamber at a pressure of 252.5 kPa for 1 h and once a day for 5 days. The immunization of C3H/He mice with sheep erythrocytes induced marked anti-sheep erythrocyte antibody response on day 7. However, this response was markedly suppressed in HBO-treated mice. The suppression is dependent on the duration of HBO and it works on the early and the late stage of antibody responses. HBO suppresses the development of both sheep erythrocyte-specific B cells and helper T cells after the immunization. Then, we tried to expose autoimmune mice to HBO. Spontaneous immunoglobulin production of NZB and MRL/lpr spleen cells was also significantly suppressed by HBO. Furthermore, long term HBO exposure results in the suppression of the development of autoimmune symptoms such as proteinuria, facial erythema and lymphadenopathy in MRL/lpr mice. All these results suggest that HBO is applicable for the treatment of autoimmune diseases.

Increased monocyte-dependent suppression of polyclonal activation of B lymphocytes from cystinotic children

In infantile cystinosis the amino acid cystine preferentially accumulates in phagocytic cells, polymorphonuclear leucocytes (PMN) and monocytes, rather than in lymphocytes. We previously described functional abnormalities in the oxidative metabolism and locomotion of cystinotic PMN and monocytes. The present study shows an abnormal lymphocyte polyclonal activation as evidenced by a decreased immunoglobulin (Ig) production and generation of Ig-containing cells (ICC) in cultures of peripheral blood mononuclear cells (PBMC) from cystinotic children upon stimulation with pokeweed mitogen and Staphylococcus aureus Cowan I. However, monocyte depletion from cystinotic PBMC fully reconstituted Ig production and ICC generation, indicating: (1) the presence of an increased monocyte-dependent suppression on lymphocyte polyclonal activation, and (2) that the intrinsic ability of cystinotic lymphocytes to respond to polyclonal stimulation was preserved. The increased cystinotic monocyte-dependent suppressive effect was not mediated by prostaglandin E2 (PGE2) since its production by cystinotic PBMC upon polyclonal activation was not different from that of controls. In addition, the sensitivity of cystinotic lymphocytes to the immunosuppressive effect of varying concentrations of exogenous PGE2 was similar to that of controls. Finally, indomethacin and 2-mercaptoethanol, two agents able to scavenge hydroxyl (.OH) radicals, restored Ig production by cystinotic PBMC, suggesting a role for reactive oxygen species in the increased cystinotic monocyte-dependent suppression.

Production of hydrogen peroxide by cutaneous T-cell lymphoma following photopheresis with psoralens and ultraviolet light

Treatment of peripheral blood mononuclear cells with 8-methoxypsoralen (8-MOP) and ultraviolet light, a procedure known as PUVA, has been found to be useful in the management of systemically disseminated cutaneous T-cell lymphoma (CTCL). In the present study we used a highly sensitive flow cytometric assay in conjunction with the hydroperoxide-sensitive dye 2',7'-dichlorofluorescein diacetate to measure intracellular hydrogen peroxide in normal lymphocytes and CTCL following PUVA treatment. Based on their laser light-scattering properties, lymphocytes were separated into three major subpopulations. We found that ultraviolet light alone caused an increase in the hydrogen peroxide content of each of the subpopulations, a response that was augmented when the cells were pretreated with 8-MOP (50 ng/ml). Cells from CTCL patients were more sensitive to the effects of 8-MOP than were normal lymphocytes. In both cell types, the production of hydrogen peroxide was found to be inhibitable by catalase. We noted an increase in hydrogen peroxide production following photopheresis; however, this was observed only 24 h after treatment. In addition, a further increase in hydrogen peroxide production was observed in lymphocytes isolated from peripheral blood that had been obtained from patients at 15 min after a second photopheresis treatment. Hydrogen peroxide is known to modulate the action of cytokines as well as the immunological responses of leukocytes. Our data suggest that the production of hydrogen peroxide by lymphocytes may be important in the action of PUVA in CTCL.

Antioxidant nutrients and immune functions--introduction

This short introduction encompasses only a small portion of the literature linking free radical production and consequent effects on immune functions. The role of essential dietary components in modulating these effects is an area of intense and expanding investigation. Each of the nutrients examined in the following chapters has distinct functions, but in this volume we concentrate on their shared capacity to act as antioxidants.

Involvement and relative importance of at least two distinct mechanisms in the effects of 2-mercaptoethanol on murine lymphocytes in culture

2-Mercaptoethanol (2-ME) exerts several effects on murine lymphocytes in culture that might explain its ability to enhance survival and growth of these cells. The uptake of the essential amino acid cystine and consequently the maintenance of intracellular glutathione levels are enhanced by 2-ME. Furthermore, 2-ME (even in the disulfide form) causes lymphocytes to release thiols into the culture medium. These effects might protect the cells from oxidative damage. The additional cystine provided by treatment of lymphocyte cultures with 2-ME might also allow adequate protein synthesis to support survival and/or growth. This study was conducted to assess the relative importance of the antioxidant and protein synthesis effects of 2-ME. As expected, 2-ME increased cystine uptake at all concentrations that enhanced growth and survival, but four nonthiol antioxidants that enhanced growth and/or survival either did not substantially affect cystine uptake or decreased it and did not affect the release of cystine or its products. The results presented here demonstrate that antioxidant protection is necessary and sufficient for lymphocyte survival and that cystine uptake in untreated lymphocytes is sufficient to support the protein synthesis needed for survival and limited growth. However, we also noted that concentrations of 2-ME that stimulated maximal growth more than doubled protein synthesis as measured at 8 hr. Thus the portion of the effects of 2-ME not accounted for by antioxidant action could be accounted for by enhanced protein synthesis.

Quantitative aspects of the feeder cell phenomenon: mechanistic implications

It has been proposed that feeder cells function by supplying lymphocytes with the amino acid cysteine (a thiol compound). The results presented here indicate that thiols are the critical element of the feeder cell phenomenon. Specifically, we noted that the rank of thiol production by four different feeder cell lines corresponds to their relative abilities to support a lymphocyte cell line, CTLL-2. In addition, increasing thiol production by the feeder cells with lipopolysaccharide increased their support of CTLL-2 cells and decreasing it with homocysteate decreased support of CTLL-2 cells. However, it was also noted that substantial (up to 79% maximal) support of CTLL-2 growth was provided by feeder cell concentrations which could not produce detectable levels of free thiols. This prompted us to propose an alternative mechanism for the feeder effect which would explain these apparently paradoxical findings.

Macrolidic antibiotics: effects on primary in vitro antibody responses

The effect of two macrolidic antibiotics, josamycin and erythromycin, on the primary immune response in cultures of human peripheral blood mononuclear cells (PBMC), were studied using a soft agar hemolytic plaque assay. Both compounds induced an appreciable reduction in the primary antibody response in total PBMC cultures. The removal of plastic-adherent cells, however, profoundly modified the effect of macrolides on the immune response. Both josamycin and, to a lesser extent, erythromycin enhanced, rather than suppressed, the antibody response. Furthermore, the macrolide-induced immunodepression in cultures of total PBMC was completely reversed by the addition of catalase (8000 U/ml). Taken together, these findings suggest that the macrolide-induced depression of the antibody response depends upon the presence of adherent monocytic cells and is mediated by the production of hydrogen peroxide.

Mercaptoethanol protects glutathione depleted cells

Buthionine sulfoximine depleted the glutathione (GSH) level of mouse lymphoma L1210A cells in culture to 6% of control and killed the cells within 48 hours in medium supplemented with fetal calf serum or bovine serum albumin. Mercaptoethanol or alpha-thioglycerol but not GSH or cysteine added to the medium protected the cells from the effect of GSH depletion. Horse serum was also protective, and this effect was removed by dialysis over 65 hours and could not be restored by adding GSH. Mercaptoethanol alone had a protective action in the dialyzed sera. The results suggest that mercaptoethanol may act independently and perform the functions of GSH.

Glutathione status of rat thymocytes and splenocytes during the early events of their ConA proliferative responses

Glutathione plays an important role in the lymphocyte mitogenic response. We have demonstrated that 2-ME increases the ConA proliferative response of rat splenocytes and in parallel, causes an enhancement of glutathione synthesis in these cells. On the other hand, 2-ME had the same action on the glutathione level of thymocytes during the late phase of their mitogenic response, but it had no effect on the [3H]thymidine uptake of these cells. To clarify this discrepancy and the role of glutathione during the mitogenic response, we studied the glutathione status of thymus cells during the early phase of the ConA-induced proliferative response in the presence or the absence of 2-ME in parallel with that of whole spleen cells and the T cell fraction of splenocytes. During the early events of the mitogenic response, i.e., during the 24th h, we observed a normal 2 GSSG/GSH + 2 GSSG ratio in cultured cells, indicating a normal redox state, and that ConA involved an increased glutathione level in thymocytes but not in whole splenocytes and in splenic T cells. 2-ME had no effect on the glutathione level of stimulated thymocytes during the early phase of the mitogenic response. This phenomenon could be related to an absence of its effect on [3H]thymidine uptake. On the other hand, 2-ME induced an enhancement of the glutathione level and [3H]thymidine uptake in the two types of stimulated splenocytes. This study suggest that thymocytes do not have the same mechanism of glutathione synthesis induction as that which occurs in splenocytes during the ConA proliferative response. This mechanism could be related to the maturation state of the T cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered metabolism and cell surface expression of glycosphingolipids caused by vitamin E in cultured murine (K3T3) reticulum sarcoma cells

Vitamin E caused a generalized reduction in the metabolism and cell surface expression of glycosphingolipids (GSL) in cultured Kirsten murine sarcoma virus-transformed nonproducer (K3T3) cells. Metabolism of gangliosides was decreased two- to fourfold in cells treated for 72 hr with 1 and 2 micrograms/ml but not with 12 micrograms/ml vitamin E compared to control cultures. This was demonstrated by a quantitative reduction in precursor 3H-galactose label incorporated in ganglioside fraction and further substantiated by thin layer chromatography of colorimetrically and radiochemically detected GSL homologues. The composition of neutral GSL homologues was only slightly changed. The cell surface expressions of sialoglycoconjugates, analyzed by selective periodate-borotritide labeling, were also diminished quantitatively. These results are discussed in light of a previously demonstrated increase in antigenicity of K3T3 cells treated with vitamin E and the reduced tumorigenicity of these cells when transplanted into mice fed vitamin E-supplemented diets.

Glutathione status during the mitogenic response of rat splenocytes. Effects of oxygen concentration: FO2 21% versus FO2 7%

Glutathione is known to be an important parameter for ConA proliferative response of murine splenocytes. We studied the glutathione status of ConA-stimulated rat splenocytes during the early and late phase of the mitogenic response under low (FO2 7%) and standard (FO2 21%) oxygen concentrations. We determined the intracellular total, oxidized and reduced glutathione levels after 6, 12, 24 and 48 h of culture with or without ConA and/or 2-ME, under FO2 7% and 21%. Our results showed that: The 2 GSSG/GSH + 2 GSSG ratio, which indicated the redox state of the cells, remained normal during the early period of culture (0-24 h), irrespective of culture conditions. After 48 h of culture, this ratio increased dramatically under FO2 21% and less under FO2 7%. The maintenance of the redox state seems to be an oxygen concentration-dependent phenomenon. ConA stimulation involved a glutathione consumption during the early stages of culture; under these conditions 2-ME increased the glutathione synthesis, which was higher under FO2 7% than under FO2 21%. On the other hand, the presence of 2-ME involved an increase of tritiated thymidine uptake in stimulated splenocytes, which was significantly higher under FO2 21% than under FO2 7%. Low oxygen tension (FO2 7%) can induce a higher increase of glutathione synthesis, whereas the respective ConA proliferative response is lower than that observed under standard O2 conditions.

Effects of antigens on mononuclear leukocyte chemiluminescence

Influenza virus and Candida albicans allergenic extract elicit alterations in the oxidative metabolic activity of human mononuclear leukocytes (MNL). MNL preparations (greater than 96% lymphocytes, less than 4% monocytes) exposed in vitro to inactivated influenza virus displayed significantly enhanced oxidative activity, as demonstrated by luminol-amplified chemiluminescence (CL). MNL from donors who had received influenza vaccine and unimmunized donors showed similar levels of virus-stimulated CL. In contrast, MNL exposed to Candida (a macrophage dependent lymphocyte stimulator) displayed significant suppression in oxidative activity. Our findings support the hypothesis that oxidative activity holds an important role in the early events of the immune response.

Lymphocyte glutathione status in relation to their Con A proliferative response

We studied the intracellular total, oxidized and reduced glutathione levels in thymus and spleen rat lymphocytes cultured with or without Con A and 2-mercaptoethanol (2-ME). After 48 h culture, the total glutathione level decreased and the oxidized glutathione level increased in the two types of unstimulated and stimulated cells. In the presence of 2-ME, the tritiated thymidine incorporation increased in splenocytes but not in thymocytes; on the other hand, the two types of stimulated cells increased their total and oxidized glutathione content. The enhancement of the GSSG/GSH + GSSG ratio, irrespective of culture conditions, indicates a severely disturbed redox state of the cells. 2-ME acts on the glutathione synthesis of stimulated lymphocytes but is unable to maintain a normal redox state of these cells.

T cell triggering by lectins. I. Requirements for interleukin 2 production; lectin concentration determines the accessory cell dependency

The requirements for lectin-induced interleukin 2 (IL2) production by human T cells have been investigated. With two different types of T cells, the Jurkat T cell lymphoma and highly purified HLA class II- peripheral T cells, the amount of IL2 produced was strongly dependent on the lectin concentration used. Addition of accessory cells caused a shift in the dose-response curve, resulting in strongly enhanced IL2 production at low concentrations. Thus, the (absolute) accessory cell dependency for T cells to produce IL2 is defined by experimental conditions. Only at lectin concentrations that were found to be optimal in the presence of accessory cells, removal of these cells abrogates IL2 production. Furthermore, after depletion of monocytes IL 2 production by peripheral T cells became almost completely dependent on the presence of thiols in the culture medium. In contrast, the IL2 production by the Jurkat line was not influenced by addition of thiols. The Jurkat model was used to study the nature of accessory cell because this cell line does not show any reactivity to allogeneic cells. Various myeloid and B lymphoid cell lines were tested as accessory cells. The capacity to function as accessory cell was not related to the monocytic origin of the cell. B cell lines were far more effective than monocytes, as two HLA class II- monocytic cell lines were not active. Even after HLA class II determinants were induced on these cells by incubation with an interferon-gamma-containing conditioned medium, they failed to act as as accessory cells. These experiments question the importance of HLA class II molecules and monokines, such as IL1, for lectin-induced IL2 production.

Augmentation of in vitro antibody response by disulfide compounds. I. Comparison between intermolecular and intramolecular disulfides

The following disulfide compounds: 2-hydroxyethyldisulfide (2-MEox), 2-aminoethyldisulfide (cystamine) and oxidized dithiothreitol (DTTox) were found to augment the in vitro antibody response to sheep erythrocytes in murine lymphocytes as effectively as their reduced forms when they were added to the culture medium. We, however, found out that the mode of action of DTTox was greatly different from that of 2-MEox or cystamine. 2-MEox and cystamine showed augmenting effects on the proliferative response to lipopolysaccharide and on the uptake of (35S)-cystine by the lymphocytes. In contrast to these intermolecular disulfides, DTTox, an intramolecular disulfide compound, was found to be inactive in these systems. 2-MEox and cystamine, but not DTTox, were reduced to thiol forms by the intact lymphocytes or by the cell homogenate. Thus, it is likely that DTTox did not behave as the reduced form in the lymphocyte culture in contrast to 2-MEox and cystamine, suggesting that the disulfide form itself plays an important role in augmenting effects of DTTox.

Depression of Con A proliferative response of immune cells by in vitro hyperoxic exposure--protective effects of thiol compounds

Time dependent response for hyperoxic exposure was determined in vitro on ConA proliferative response of rat splenocytes, peripheral blood mononuclear cells and thymocytes. The proliferative responses were evaluated after different lengths of hyperoxic exposure (12-72 h, FiO2 = 0.95). After 24 h oxygen exposure, the spleen cell viability assessed by dye exclusion was normal but DNA synthesis was markedly suppressed in the above three types of cells. Total or partial protection of the mitogenic response to ConA was obtained by 2-mercaptoethanol, reduced glutathione or L-cysteine addition in culture medium; only selenomethionine had no protective effect. Thymic cells showed a different response-curve: after 6 h exposure to normobaric oxygen DNA synthesis was decreased and was not restored by any of the thiol compounds tested. In this respect, these cells demonstrated different susceptibility to an oxidant injury, i.e. exposure to high oxygen concentration. From a pharmacological point of view O2 exposure and altered immune response could be proposed as a useful model for screening the antioxidant drug activity.

Effect of dietary 2-mercaptoethanol on the life span, immune system, tumor incidence and lipid peroxidation damage in spleen lymphocytes of aging BC3F1 mice

The age-related decline in immune function, which is thought to be responsible for the increased incidence with age of certain diseases, including cancer, has been attributed primarily to a loss of T-lymphocyte function. As free radical reactions may contribute to cellular deterioration and loss of cell function with age, we investigated the effect of adding an immunopotentiating antioxidant, 2-mercaptoethanol (2-ME), to the diet of BC3F1 mice in a longitudinal study. For the study, young mice were divided into two groups, one of which received the 2-ME-supplemented diet. Approximately every 3 months for 2.5 years, mice from each group were sacrificed and the spleen lymphocytes assessed for immune function (proliferative response to concanavalin A, phytohemagglutinin, and lipopolysaccharide and the humoral response to sheep red blood cells). The accumulation of fluorescent products indicative of free radical damage was measured in the spleen lymphocytes and the cytochrome P-450 content and activity assessed in the liver. The effect of the 2-ME-supplemented diet on the mean and maximum life span and tumor incidence was also determined. The results showed that the animals fed the 2-ME diet had an increased mean and maximum life span and a postponed onset and decreased incidence of tumors. In general the T-cell-dependent immune responses were higher in the 2-ME-fed mice compared to the controls when the animals were young. No difference was observed between the two groups during mid-life. The responses declined in both groups during the latter half of the life span, but the responses of the 2-ME-fed animals declined to a lesser extent. The accumulation of fluorescent products of lipid peroxidation damage was also delayed in the lymphocytes of the 2-ME-fed mice. Cytochrome P-450 content and activity in the liver was not different in the two groups. The results suggest that the antioxidant activity of 2-ME delayed the accumulation of free radical damage in spleen lymphocytes, which resulted in a delay in the decline of immune function and was associated with the decreased tumor incidence and increased life span.

Macrophage support and suppression in rabbit T cell mitogenesis

The role of macrophages in mitogen-induced rabbit T cell proliferation has been investigated. The blastogenic response to the 3 mitogens, PHA, ConA and oxidative treatment by neuraminidase and galactose oxidase (NaGo) was tested. T cell proliferation was reduced by removal of low density or plastic adherent cells, including macrophages, and could be enhanced by the addition of peritoneal resident macrophages, indicating a macrophage requirement for rabbit T cell proliferation. However, PHA-induced proliferation could not be raised to the level expected. It was found that catalase and especially 2-ME could considerably enhance macrophage dependent proliferation, even at low macrophage concentrations. It is concluded therefore, that macrophages not only support but also suppress lymphocyte proliferation, namely by non-specific damage to lymphocytes through release of radicals and hydrogen peroxide. In addition, peritoneal, but not lymph node macrophages were found to suppress lymphocyte proliferation by prostaglandin production, although to a lesser extent. Experiments, done in the presence of blockers of macrophage-mediated suppression, showed that macrophages were able to magnify the PHA-induced T cell proliferation to the expected values. The experiments thus show that unactivated macrophages support and suppress lymphocyte proliferation at the same time.

Analysis of the effects of erythrocytes on mitogen-dependent clonal proliferation of murine B lymphocytes

Addition of intact erythrocytes to semisolid agar cultures of murine B cells dramatically improves cloning efficiency and affects colony morphology. In this study, we investigated possible mechanisms through which this might occur. Specific modification of sheep erythrocyte (SRBC) membranes by treatment with trypsin but not other enzymes improved colony potentiation and erythrocytes from rats, mice, and humans were also effective after trypsin treatment. In addition, autoantibody-coated murine erythrocytes were superior to normal cells in this regard. These observations suggest that erythrocytes enhance lymphocyte survival and/or proliferation by means of particular membrane-mediated processes. The possible importance of erythrocytes as scavengers of toxic hydroxyl radicals was also investigated. Deliberately generated radicals formed by addition of dihydroxyfumaric acid and iron were effectively countered by addition of SRBC. More detailed analyses revealed that of several endogenously produced toxic species, hydrogen peroxide may be the most important under ordinary culture conditions. That is, addition of catalase but not superoxide dismutase or mannitol improved cloning efficiency in cultures lacking SRBC. These studies suggest that erythrocytes have a beneficial effect on lymphocyte survival and function in culture through at least two mechanisms.

Antigen-dependent colonies of human peripheral blood lymphocytes: an immunomorphologic study

Human peripheral blood mononuclear cells (PBMC), stimulated by sheep red blood cells (SRBC), focally proliferate in agar and form colonies of anti-SRBC antibody-secreting cells surrounded by hemolytic areas. Two types of colonies develop: type I (diffuse type), which grows deeply into the agar, and type II (compact type), which grows above the former. Immunochemical and ultrastructural studies show that diffuse colonies contain differentiating lymphoid cells, from small lymphocytes to mature plasma cells. About 50% of cells stain positively in their cytoplasm for IgM and only 1-2% for IgG. Most colonies produce light chains of one class, whereas only a few produce both classes. Many cells resemble monocytes or T lymphocytes in their general morphology and lie in close contact with immunoglobulin-positive cells. Compact colonies contain cells not engaged in antibody production. The culture system described here is the first available antigen-dependent colony assay for human PBMC and may be useful for in vitro studies on the mechanism of human B-cell activation.

Antibody production in cultured blood lymphocytes from breast cancer patients

Peripheral blood lymphocytes from female patients with early breast cancer were examined before surgery for their ability to develop a primary antibody response in vitro against sheep red blood cells in soft agar cultures containing autologous plasma. After 6 days incubation, foci of proliferating hemolysin-forming cells surrounded by a lytic area were detected on the surface of the plates and counted with a dissection microscope; this response was antigen-dependent and antigen-specific. We applied this assay to a group of women suffering from early breast cancer and devoid of distant metastases. From our data, it appears that if all the patients are grouped together, cancer-bearing women produce somewhat fewer (P less than 0.05) haemolytic foci than healthy controls. However, division of the cancer patients into two subgroups, according to the TNM pretreatment clinical classification of regional lymph nodes, generated an interesting finding: N1 patients (N1b or N1a) produced definitely fewer foci than N0 patients, and the difference was highly statistically significant (P less than 0.001). The depression of anti sheep red blood cell antibody production observed in N1 patients was unrelated to the presence or absence of metastatic growth in their regional lymph nodes.

The stimulation of rat bone marrow fibroblast colony formation by 2-mercaptoethanol

The definition of the function of bone marrow stromal cells in the regulation of hematopoiesis has been complicated by the limited growth of these cells in vitro. We have demonstrated that the addition of 2-mercaptoethanol to rat bone marrow cultures enhances bone marrow fibroblast proliferation as evidenced by a 2-fold increase in the total number of fibroblast colonies and a 5-fold increase in the number of these colonies which contain more than 80 cells. We also present evidence suggesting that enhancement of fibroblast growth may not be due to direct action of 2-mercaptoethanol, but may result from the activation of a serum component. The results from this study should facilitate further research into the function of bone marrow fibroblasts in the regulation of hematopoietic cell differentiation.

Mechanism of augmentation of the antibody response in vitro by 2-mercaptoethanol in murine lymphocytes. II. A major role of the mixed disulfide between 2-mercaptoethanol and cysteine

Five thiol compounds including 2-mercaptoethanol (2-ME) were examined for their augmenting effects on in vitro antibody response to sheep erythrocytes. Three compounds were effective with the following order of activity; 2-ME greater than dithiothreitol greater than cysteamine. Glutathione and thioglycollate failed to enhance the response. The same order or effectiveness was seen in the stimulation of [35S]cystine uptake by murine lymphocytes by these thiols. Murine lymphocytes took up cysteine five to six times more rapidly than cystine. It is, however, unlikely that 2-ME stimulation of cystine uptake is solely due to the reduction of cystine into cysteine, because 2-ME was still stimulatory after free thiol groups had disappeared in the medium containing 2-ME and [35S]cystine. The mixed disulfide of cysteine with 2-ME (Cys-2-ME) was found to be an only product after free thiols had been oxidized. [35S]Cys-2-ME was taken up by the lymphocytes with a comparable rate to cysteine via a transport system common to that of leucine and phenylalanine. Cysteine was, however, transported via a different route. It was observed that Cys-2-ME was readily metabolized to cysteine and glutathione after the uptake. Cys-2-ME added to cystine-free RPMI 1640 medium could support the antibody response as efficiently as cystine plus 2-ME. These observations strongly suggest that 2-Me stimulates cystine uptake and, therefore, enhances the antibody response through the formation of the mixed disulfide with cysteine.

Inhibition of lymphocyte proliferation and antibody production in vitro by silica, talc, bentonite or Corynebacterium parvum: involvement of peroxidative processes

This study was undertaken to determine whether and by what means particles which induce granulomata in vivo can affect murine spleen lymphoproliferative and antibody responses in vitro. Particles of silica, talc, Bentonite or C. parvum cells inhibited lipopolysaccharide- or concanavalin A-stimulated proliferation and sheep red blood cell-induced antibody response in vitro. The inhibition required at least 48 hours exposure of the cells to the particles. The late onset of inhibition and its reproducibility at different cell or mitogen concentrations implicated particle-induced injury to both phagocytes and lymphocytes. Either alpha-tocopherol or 2-mercaptoethanol prevented the particle-induced inhibition of spleen cell responses. alpha-Tocopherol and 2-mercaptoethanol have in common the capacity to protect cells against membrane lipid peroxidation. The inhibitory peroxidative process(es) implicated by these studies are most likely attributable to: (a) stimulation of oxidative metabolism of phagocytic cells by particles; and (b) iron-catalyzed peroxidation directly by the particles. These data may be relevant in understanding the pathogenesis of and devising therapeutic approaches toward various granulomatous conditions.

Mechanism of augmentation of the antibody response in vitro by 2-mercaptoethanol in murine lymphocytes. I. 2-Mercaptoethanol-induced stimulation of the uptake of cystine, an essential amino acid

The mechanism of augmentation of the primary antibody response in vitro by 2-mercaptoethanol (2-ME) was investigated. By using cystine-free RPMI 1640 medium, it was demonstrated that cyst(e)ine was absolutely required for eliciting the following murine lymphocyte reactions: antibody response to sheep erythrocytes, proliferative response to concanavalin A or lipopolysaccharide (LPS), and polyclonal antibody response induced by LPS. The maximal antibody response was attained with 2.5-5 mM cysteine or half-cystine. The serial feeding of fresh cysteine markedly amplified its capacity to support antibody response particularly when cysteine concentration was suboptimal. Such an effect was not observed in the serial addition of cystine. On the other hand, the dose-response curve of cystine was dramatically shifted to lower concentrations by the addition of 2-ME (1 x 10(-5) M), which alone could not elicit the antibody response in the absence of cystine, nor could it augment furthermore the maximal response induced by 2.5 mM half-cystine. Commercially available RPMI 1640 medium contains 0.41 mM half-cystine, which proved to be a suboptimal concentration for eliciting the maximal response. 35S-cystine was incorporated into murine lymphocytes five to six times more slowly than 35S-cysteine. The rate of cystine uptake, however, was accelerated by 2.5-fold in the presence of 1 x 10(-5) M 2-ME. A close correlation was observed between dose-response profiles of 2-ME in augmenting the antibody response and the stimulation of cystine uptake. These results strongly suggest that one of the roles of 2-ME in augmenting the antibody response in vitro is to facilitate the use of cystine contained in RPMI 1640 medium only at a suboptimal concentration.