Effect of macrophage activation on killing of Listeria monocytogenes. Roles of reactive oxygen or nitrogen intermediates, rate of phagocytosis, and retention of bacteria in endosomes

The role of macrophage activation in the killing of L. monocytogenes is unclear. Some studies suggest that activation for enhanced production of reactive oxygen and nitrogen intermediates may not be of central importance. Recent data have indicated an important role for interferon-gamma (IFN-gamma) induced retention of L. monocytogenes in endosomes. Data from the present study indicate that proteose peptone-elicited macrophages from DBA2/J, CD-1, and C3H/HeN mice are listericidal. Activation of these cells in vitro for 20 h by IFN-gamma (20 or 500 U/ml) increased H2O2 or nitrite production, but did not increase the number of L. monocytogenes killed during a subsequent 6-h or 7-h culture. Incubation of macrophages with IFN-gamma plus lipopolysaccharide (LPS) caused greater activation and increased the number of Listeria killed during a 6-h or 7-h culture. However, this seems primarily attributable to enhanced phagocytosis. Proteose peptone-elicited macrophages were significantly more effective than resident macrophages in preventing the escape of L. monocytogenes from endosomes into the cytoplasm. This capability was not significantly enhanced by IFN-gamma in vitro, but was enhanced by IFN-gamma plus LPS. This correlates well with the effects of these activation stimuli on killing of L. monocytogenes by proteose peptone-elicited macrophages. These results indicate that enhanced retention of L. monocytogenes in endosomes is induced by proteose peptone elicitation and that further macrophage activation in vitro by IFN-gamma does not improve listericidal activity.

Immunotoxicological characteristics of sodium methyldithiocarbamate

This study was conducted to assess immunotoxicological effects and selected general toxicological effects of sodium methyldithiocarbamate (SMD). Initially, the compound was administered orally to female B6C3F1 mice at 300 mg/kg/day for 3, 5, 10, or 14 days. Body, liver, kidney, spleen, and thymus weights were measured. Selected hematological and bone marrow parameters were examined. Flow cytometric analysis was used to assess changes in lymphocyte subpopulations in the thymus and spleen, and production of antibody-forming cells in vitro was measured. Major effects included decreased thymus weight at all time points; increased spleen weight after 10 or 14 days of exposure, increased bone marrow cellularity after 10 or 14 days of exposure, significant decreases in mature lymphocyte subpopulations which were greater in the thymus than in the spleen, relatively selective depletion of the major subpopulation of thymocytes (CD4+CD8+), and decreased body weight. Overall patterns of changes were consistent with the conclusion that SMD rapidly depletes most CD4+CD8+ thymocytes, more slowly depletes a smaller number of mature lymphocytes in the thymus and spleen, and induces compensatory and/or detoxication mechanisms after 10-14 days of exposure. Subsequent experiments were done to assess selected immune function parameters. SMD at 50-300 mg/kg/day for 7 days caused substantial, dose-dependent suppression of NK cell activity. No suppression of antibody production in vivo or splenocyte responses to mitogens or allogeneic lymphocytes in vitro was detected. NK cell activity, thymus weight, and CD4+CD8+ thymocyte numbers were suppressed by dermal administration of SMD.(ABSTRACT TRUNCATED AT 250 WORDS)

Levamisole meets sulfhydryl requirements of CTLL-2 cells and mediates enhanced proliferative response to mitogen stimulation without increasing interleukin-2 production

We examined the effect of levamisole (LMS) on the proliferative response and interleukin-2 (IL-2) concentration in OKT3-, phytohemagglutinin-, and concanavalin-A-stimulated lymphocyte cultures. Although proliferative response was enhanced in lymphocyte cultures stimulated in the presence of LMS, similar levels of IL-2 were observed in stimulated and unstimulated cultures. The mechanism of the enhancement effect of LMS on proliferative response was further characterized by studying its effects on the growth of IL-2-dependent CTLL-2 cells in culture. Since this cell line has been shown to require 2-mercaptoethanol (2-ME) for normal growth in recombinant IL-2, the effect of LMS on several parameters of its growth was compared with that of 2-ME. Unlike 2-ME, LMS did not enhance 35S-cystine uptake. Both compounds increased thiol concentration in the cell culture, but (oxidized) 2-ME induced a greater increase. Generally, the effects of LMS on CTLL-2 growth were quite similar to those of structurally unrelated compounds known to have antioxidant properties, and the demonstrated thiol requirement of this cell line for growth in recombinant IL-2 was met by substituting LMS for 2-ME. When the effect of LMS on IL-2 receptor (IL-2R) expression in CTLL-2 cells was examined by a receptor-ligand binding assay involving low levels (10-80 pM) of 125IL-2, a modest increase in the level of IL-2R expression was observed. The biologically active high-affinity IL-2R complex is believed to be preferentially bound at the low levels of 125IL-2 used here, suggesting a functional relevance for this effect of LMS. These observations should be useful in minimizing the cost and duration of in vitro expansion of lymphocytes for use in adoptive immunotherapy and should be applicable in improving the response of immunologically impaired patients to immunotherapy.

Characteristics of MTT as an indicator of viability and respiratory burst activity of human neutrophils

In the present study, we have examined the suitability of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) for assessing the viability and respiratory burst activity of human neutrophils. MTT is a good indicator of the relative viability of neutrophils which have been in culture up to 24 h, if sufficient serum (10% fetal calf serum) is present in the medium and the cells being compared have been in culture for a similar period of time. However, it is not suitable for exact assessment of percent viable cells in a cell population with low viability. The effectiveness of MTT as an indicator of respiratory burst activity is demonstrated by the sharp increase in MTT reduction induced by respiratory burst stimuli and by the ability of superoxide dismutase to inhibit 75% of MTT reduction by stimulated neutrophils. Unlike nitroblue tetrazolium (which is reduced primarily intracellularly) and cytochrome c (which is reduced extracellularly), MTT is apparently reduced both intracellulary and extracellulary by activated neutrophils.

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: direct assessment of enhanced cystine uptake by lymphocytes

It has been suggested that feeder cells and 2-mercaptoethanol enhance the survival and growth of murine lymphocytes in culture by increasing cysteine availability. We previously reported that although feeder cells produce thiols, they support lymphocyte growth at densities too low for measurable thiol production. This suggested that increasing the availability of cysteine might not be the major mechanism of feeder cell action. In the present study, [35S] cystine was used to directly monitor cyst(e)ine uptake in lymphocyte-feeder cell co-cultures. The results demonstrate that feeder cells substantially increase cyst(e)ine uptake by lymphocytes, even in the absence of detectable free thiols. Data are presented which suggest an explanation for this unexpected observation.

Circadian variations of human lymphocytes are not responsible for contradictory or variable results in studies of IL-2 production

Efforts to correlate various immunological disorders with alterations in IL-2 production in vitro have led to highly variable and often contradictory results. One possible contributing factor to these results could be the existence of circadian variations in the capacity of lymphocytes to produce IL-2 in culture. Although there were reasons to suspect that such variations might exist, the present study revealed no significant variations in 6 of 10 normal subjects in three experiments or in the mean values for all subjects at each of three sample acquisition times. In addition, no subject exhibited circadian variations in all three experiments. Since it was possible that failure to detect variations was due to selection of an inappropriate mitogen or inappropriate culture conditions, 2 mitogens and various culture conditions were used. Circadian variation was noted for only one subject out of eight under only one set of conditions. This suggests that circadian variations are not responsible for variable or contradictory results which have been reported. Therefore, the recently reported circadian variations in T helper to T suppressor ratios do not seem to significantly affect mitogen-induced IL-2 production.

Potential immunomodulatory activity of phenylphosphonothioates

In the course of immunotoxicological studies of several organophosphorous compounds, it was noted that some phenylphosphonothioates enhanced the activation of rat splenocytes by concanavalin A. In the present study some of these compounds were compared to the well-characterized immunomodulatory thiol, 2-mercaptoethanol (2-ME). Two of the compounds are able to substitute for 2-ME and allow near maximal growth of a strictly 2-ME-dependent lymphocyte cell line (CTLL-2). These compounds exhibit essentially additive effects with 2-ME on CTLL-2 cells and rat splenocytes. In agreement with previous results with 2-ME, the phosphonothioates have essentially no effect on interleukin-2 production in mitogen-stimulated splenocyte cultures. One phosphonothioate, as well as its possible thiol hydrolysis product, supports cell survival and enhanced cystine incorporation by CTLL-2 cells. However, 2-ME was more effective in stimulation of enhanced generation of extracellular thiols than were the other agents. These results suggest very similar modes of action for phosphonothionates and 2-ME. Finally, a phosphonothioate selected for low neurotoxic potential was examined and found to effectively support lymphocyte growth in vitro and to exhibit relatively low acute toxicity in mice.

The role of thiols in lymphocyte responses: effect of 2-mercaptoethanol on interleukin 2 production

The effects of 2-ME on the production of IL2 in mitogen-stimulated mouse splenocyte cultures were examined. Since 2-ME could conceivably affect IL2 production and utilization equally, resulting in no apparent change in the IL2 concentration of treated cultures, 12-h cultures were used to minimize any effects of IL2 utilization on the IL2 concentrations observed. Utilization of IL2 in 12h splenocyte cultures was estimated by means of simulations in which IL2 from 12h culture supernates was utilized by CTLL-2 cells comparable in number to the lymphoblasts present in splenocyte cultures. These stimulations indicate that IL2 utilization is insignificant during the first 12h of culture under a variety of conditions. Thus, the IL2 concentration at 12h reflects predominantly the rate of production. No effect was observed on IL2 concentrations at 12h when cultures were treated with 2-ME under conditions in which the 2-ME enhanced cellular activation/proliferation. These results indicate that 2-ME does not enhance proliferation in Con A-stimulated splenocyte cultures by increasing IL2 production, but by some other mechanism(s).

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.

Effects of paraoxon, p-nitrophenol, phenyl saligenin cyclic phosphate, and phenol on the rat interleukin 2 system

Two organophosphorus compounds, paraoxon and phenyl saligenin cyclic phosphate, as well as p-nitrophenol and phenol which are structurally related to paraoxon, were tested for their effects on interleukin 2 (IL2) production and responsiveness by rat splenocytes in vitro. Three of the four compounds inhibited mitogen-induced lymphocyte proliferation as well as IL2 production and responsiveness. However, phenyl saligenin cyclic phosphate produced maximal inhibition at a much lower concentration (0.5 microM) than p-nitrophenol (200 microM) or paraoxon (200 microM). Phenol was not inhibitory at any concentration tested (up to 250 microM). Since the production of and response to IL2 are key events in immune responses, compounds which suppress these events can be identified as potential suppressors of host resistance to disease.

Apparent interleukin 2 (IL-2) inhibitory activity of human serum is due to rapid killing of IL-2-dependent mouse cells

A number of investigators have reported that human serum inhibits the proliferation of IL-2-dependent mouse cells in IL-2 bioassays, but the mechanism of inhibition has not been carefully examined. We noticed that IL-2-dependent mouse cells (CTLL-2) are killed within 30 min in the presence of a 1/10 dilution of human serum. However, CTLL-2 cells totally deprived of IL-2 did not begin to die until at least 6 h in culture. Thus, even complete inhibition of IL-2 by human serum could not account for the rapid cytotoxicity caused by human serum. Since humans have 'natural' antibodies which react with mouse cells, it seemed possible that the cytotoxicity was due to antibody/complement-mediated cell lysis. This was supported by the observation that EDTA (at a concentration sufficient to inhibit complement) protected CTLL-2 cells from the cytotoxic effects of human sera from four normal donors. In addition, preincubation of CTLL-2 cells with heat-inactivated human sera at 4 degrees C rendered them much more susceptible to lysis with rabbit complement than cells which were preincubated with complete culture medium. The cytotoxicity of human serum is not limited to IL-2-dependent mouse cells but was also observed with EL4 and Ag8.653 cells as well as normal splenocytes. The cytotoxic effect of human serum was lost upon removal of IgM, but not upon removal of IgG. These results strongly suggest that the inhibition of proliferation of IL-2-dependent mouse cells by human serum is due to antibody/complement-mediated lysis of those cells. In addition, non-heat-inactivated human serum did not inhibit the IL-2-mediated proliferation of human PHA blasts, indicating that there is no inherent inhibitory activity in human serum apart from the cytotoxic effect on xenogeneic cells. Thus the reported IL-2 inhibitory activity of whole human serum is probably not biologically relevant.

Suppression of interleukin 2 activity by natural products: effects of serum lipoproteins

The results presented here demonstrate that mouse serum lipoproteins inhibit Interleukin 2 (IL2)-mediated proliferation of CTLL-2 cells. Lipoproteins account for a variable portion (29-83%) of the total inhibitory activity of whole serum and are not specific inhibitors of IL2-mediated cell proliferation, as evidenced by their inhibitory activity for non-IL2-dependent MPC 11 cells. Lipoproteins did not accelerate the death of CTLL-2 cells deprived of IL2, indicating that their inhibition of proliferation is not due to toxic effects. Finally, the inhibitory activity of serum and isolated lipoproteins was increased when the donor mice were maintained on a diet high in polyunsaturated fats for 16 days prior to bleeding. These findings provide a basis for future investigations of the relationship between dietary fats, lipoprotein quantity and composition, and alteration of immune responses.

A quantitative, non-isotopic bioassay for interleukin 2

A quantitative bioassay for IL2 is described in which an electronic particle counter is used to measure IL2-mediated proliferation of an IL2-dependent cell line. The assay requires no radioisotopes, is comparable to tritiated thymidine incorporation and can be completely performed in about 28 hours. It can also be used to measure inhibition of IL2-mediated proliferation.

Biochemical characteristics of the heterophile transplantation antigen (HT-A)

The Heterophile Transplantation Antigen (HT-A) is a clinically important antigen which is found in some human kidneys and on the erythrocytes and in the serum of rats and some other mammals. Recent reports suggest the possibility that the anti-HT-A antibodies responsible for graft rejection may cross react with one or more HL-A specificities. The ideal way to investigate this possibility would be to perform careful serological and biochemical comparisons of purified HT-A and HL-A. We report here the first stage of these investigations, the examination of the biochemical properties of HT-A. The HT-A molecule of rat plasma is apparently a glycoprotein with a molecular weight greater than 1,000,000. The HT-A antigenic determinant site seems to reside in the carbohydrate portion of the glycoprotein. The native HT-A molecule is apparently susceptible to proteolytic enzymes of rat plasma and serum and is cleaved by these enzymes to produce a fragment with a lower apparent molecular weight and a larger fragment which coelutes with lipoproteins during Sepharose CL-4B chromatography. The data presented here should allow development of a rational purification scheme for the HT-A glycoprotein of rat plasma to be used in further studies in the relationship between HT-A and HL-A.

The heterophile transplantation antigen (HT-A) system: a unique heterophile system exhibiting multiple specificities

Although many characteristics of the heterophile transplantation antigen (HT-A) system have been determined, definitive information regarding certain aspects of the system is still lacking. In an effort to obtain such information concerning the number of HT-antigen and antibody specificities (i.e. single or multiple) and the distribution of HT-A among selected mammalian and avian species, the present study was conducted. In this study, the ability of erythrocytes from several species to absorb the anti-HT-A activity from 6 anti-HT-A sera was determined with a quantitative inhibition of hemagglutination assay utilizing an electronic particle counter. Careful analysis of the results of these experiments indicated the existence of multiple (i.e. 5 or more) HT-antigen and antibody specificities. The distribution of these HT-antigens among selected mammalian and avian species was not identical to the distribution of any well-characterized heterophile antigen of which we are aware. Therefore, none of the HT-A specificities defined in this study are identical to previously described heterophile antigens. These findings confirm and expand previous knowledge of the HT-A system and have facilitated formulation of hypotheses regarding the role of multiple specificities in acute renal allograft rejection and the genetics of HT-A expression in humans.

Quantitation of proteins in the femtomole range by hemagglutination using an electronic particle counter

By using an electronic particle counter equipped with two counting channels, it is possible to simultaneously count total particles and agglutinated particles in an erythrocyte population. Using these two parameters, an empirically useful measure of the degree of agglutination in a sample (the agglutination index) can be generated. This method has been used to accurately and precisely determine human serum IgG concentrations in an inhibition of hemagglutination assay. As little as 1 microgram/ml of IgG could be measured in this way. Agglutination and inhibition of agglutination assays with other systems indicate that this method will be widely applicable.