Regulation of lymphocyte responses in vitro. V. Suppressor activity of adherent and nonadherent rat lymphoid cells

Characterization of Novel Lactobacillus fermentum from Curd Samples of Indigenous Cows from Malnad Region, Karnataka, for their Aflatoxin B1 Binding and Probiotic Properties

Thirty-four isolates of Lactobacillus spp. (LAB) from 34 curd samples were evaluated for their aflatoxin B₁ (AFB₁) binding and probiotic properties. Upon characterization, four LAB isolates (LC3/a, LC4/c, LC/5a, and LM13/b) were found to be effective in removing AFB₁ from culture media with a capacity of above 75%. Staining reaction, biochemical tests, pattern of sugar utilization, and 16s rRNA gene sequence analysis revealed the identity of all the four isolates as L. fermentum. All of them could tolerate acidic pH, salt, and bile, which promise the use of these probiotic bacterial isolates for human applications. These isolates showed poor hydrophobicity and higher auto-aggregation properties. All L. fermentum isolates were found susceptible to gentamycin, chloramphenicol, cefoperazone, ampicillin, and resistant to ciprofloxacin and vancomycin. Results of hemolytic and DNase activity indicated their nonpathogenic nature. Though all L. fermentum isolates found inhibiting the growth of Salmonella ebony, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa, maximum inhibition was obtained with isolate LC5/a. Kinetic studies revealed that all four bacteria required a minimum of 2 h to reach stationary phase of AFB₁ binding. AFB₁ binding ability varied from 66 to 85.2% among these four isolates. Bile (0.4%) was significant (P ≤ 0.05) in reducing the AFB₁ binding property of isolates LC3/a, LC4/c, and LM13/b, while increased AFB₁ binding ability was recorded at acidic pH (2.0). AFB₁ binding properties of isolate LC5/a were found least affected by acidic pH and bile. The findings of our study revealed the higher efficiency of L. fermentum isolate LC5/a in reducing the bioavailability of AFB1 in gut, and additionally, it improves the consumers' health by its various probiotic characters. These beneficial characters, L. fermentum isolates, promise them to use as probiotic formulations alone or in combinations with other beneficial probiotic-bacterial isolates.

Glucocorticoids enhance concanavalin A-induced mitogenic response through the inhibition of nitric oxide production

Glucocorticoids (GC) are known to inhibit mitogen-induced proliferation of T cells. In this study we show two experimental situations where the addition of GC increases lymphocyte proliferation. It has been reported by different authors that rat spleen (SPL) cells proliferate poorly after concanavalin A (Con A) activation. These poor responses have been related to the suppressor activity of macrophages. Similarly, it is known that T-cell proliferation is depressed in the presence of an excess of macrophages in the culture. Here we show that in both experimental situations, the inclusion of dexamethasone (DEX), a synthetic glucocorticoid, in the culture medium enhances the Con A-stimulated proliferation. We provide evidence that this effect is a consequence of the inhibition of nitric oxide (NO) synthesis by the hormone. Furthermore, we also demonstrate that rat SPL cells are inefficient antigen-presenting cells (APC) because of their spontaneous high production of NO. Taken together our results suggest that the effects of GC on T-cell activation may be to promote or inhibit proliferation depending on the level of endogenous NO synthesis. The possible significance of these results is briefly discussed.

Evidence for the involvement of macrophage-derived nitric oxide in the modulation of immune status by a conditioned aversive stimulus

Prior work in our laboratory has demonstrated that exposure to a conditioned aversive stimulus developed through pairings with electric shock results in pronounced alterations of immune status. These conditioned alterations of immune status include a decreased in natural killer cell activity, decreased production of interleukin-2 and gamma-interferon by concanavalin A (ConA)-stimulated splenocytes and a profound suppression of the mitogenic responsiveness of T and B lymphocytes to mitogens. The present study examines the role of macrophage-derived nitric oxide in the conditioned stimulus-induced suppression of lymphocyte proliferation by measuring the level of nitrite accumulation in culture, determining the effect of macrophage depletion, and assessing the effect of NG-monomethyl-L-arginine (L-NMMA), a specific inhibitor of the L-arginine-dependent nitric-oxide synthesizing pathway, alone and in combination with L- or D-arginine. The results show that the conditioned suppression of the mitogenic responsiveness of splenocytes to ConA is accompanied by a marked increase in nitrite accumulation. Both the depletion of macrophages and the addition of L-NMMA attenuates the conditioned suppression of ConA-stimulated lymphocyte proliferation. Furthermore, the addition of excess L-arginine, but not D-arginine, counteracts the effect of L-NMMA. The present findings show that the neuroendocrine alterations induced by a conditioned aversive stimulus suppress lymphocyte proliferation through alteration of the production of nitric oxide by macrophages.

Inhibition of chronic relapsing experimental allergic encephalomyelitis in the Biozzi AB/H mouse

Chronic relapsing experimental allergic encephalomyelitis (CREAE) can be reproducibly induced in Biozzi AB/H mice following injection of spinal cord homogenate (SCH) emulsified in complete Freund's adjuvant (CFA). Active clinical disease is associated with mononuclear cell infiltration of the central nervous system (CNS), mainly the spinal cord. Whole brain homogenate (BH), however, failed to induce clinical or histological disease. In contrast, substituting sciatic nerve homogenate in the inoculum induced experimental allergic neuritis (EAN). Clinical disease was manifest earlier (13.1 +/- 0.3 days) than CREAE (16.2 +/- 1.4) and was accompanied by mononuclear infiltration of the peripheral nervous system (PNS). In comparison to CREAE induction, pretreating mice with SCH or BH in incomplete Freund's adjuvant (IFA) suppressed the development of SCH-induced disease. The BH was more tolerogenic than the SCH and this hyporesponsiveness was CNS antigen-specific as PNS tissue failed to inhibit the course of CREAE. Tolerance induced by pretreatment with SCH or BH in IFA was reversed by a single injection of 200 mg/kg cyclophosphamide, 2 days prior to CREAE induction. This suggests that IFA-induced hyporesponsiveness is actively regulated, possibly via the action of suppressor cells. In addition, treatment with neuroantigens in IFA appears to be mainly afferent acting as it serves to prevent initial disease induction. This treatment after immunization for CREAE, however, fails to prevent disease progression. Furthermore, treatment with CNS antigens emulsified in IFA during the post-acute remission stage appeared to synchronize and induce (32 +/- 1 days) the onset of clinical relapse, compared with untreated controls (41 +/- 5 days). This indicates that such IFA treatment has minimal value in controlling an ongoing immune disease of the CNS.

Cell-mediated inhibition of proliferation and activation of alloreactive cytotoxic lymphocytes: maintenance of response potential of precursors and dissociation between proliferation and effector function of activated cytotoxic lymphocytes

Adherent layers of macrophages (M phi-c) generated in vitro from splenic precursors inhibit lymphoproliferative responses to mitogen and to alloantigen without inhibiting the production of interleukin-2 (IL-2). Analysis of spleen cells stimulated for 48 hr in the presence of M phi-c indicated that both blastogenesis (increased cell mass) and expression of IL-2 receptors (7D4 determinants) were reduced. Analysis of BrdU incorporation (frequency of S-phase cells) and total cellular DNA revealed that the M phi-c inhibited the progression from G1 to S phase of cell cycle. The M phi-c not only inhibited the proliferative response to alloantigen but also prevented the generation of alloreactive cytotoxic T cells. The M phi-c were shown not to inhibit CTL responses by eliminating the stimulators or by inactivating precursors or inducing suppressors. The M phi-c were affecting the induction of CTL activity since the M phi-c did not affect the expression of cytolytic activity by activated CTL. The M phi-c did inhibit the proliferation of the activated CTL, suggesting that although cytolytic activity can be expressed in G1 phase of cell cycle, the activation of cytolytic activity in CTL-P may require a G1 to S phase transition. The cells recovered from 5-day MLC incubated in the presence of M phi-c were fully capable of generating a subsequent CTL response. This is in contrast to cells recovered from unstimulated cultures (no M phi-c) which have lost the ability to generate CTL responses. The M phi-c therefore prevent the generation of CTL responses in a totally reversible fashion, so as to allow activation and proliferation of CTL-P which have been removed from the influence of the M phi-c. These observations are discussed in the context of the currently hypothesized role of tissue macrophages in microenvironmental regulation.

An intrinsic suppressor cell-controlling formation of autologous rosettes in peripheral mouse lymphocytes

The existence of intrinsic suppressor cell-controlling autologous rosette formation in mouse peripheral blood lymphocytes was demonstrated. This cell is glass adherent, Thy 1,2 positive, and loses its activity after treatment with monoclonal anti-Lyt 2 antibodies plus complement. Suppression of the autologous rosette formation also involves a factor released by these cells directed against autologous erythrocytes. The suppressive phenomenon is strain specific.

Differences in the effect of indomethacin and preincubation on the lymphoproliferative response to concanavalin A of spleen cells from low responder C57BL/6 and high responder BALB/c mice

In vivo treatment with 100 micrograms of indomethacin each 48 h for 2 weeks enhanced the proliferative response to concanavalin A (Con A) of spleen cells from mice of the C57BL/6 (B6) strain, low responder to T cell mitogens, but did not modify the response of spleen cells from mice of the high responder strain BALB/c (C). The enhancing effect of in vivo indomethacin treatment was more marked in cultures of B6 splenocytes stimulated with high, moderately supraoptimal doses of Con A than in cultures stimulated with optimal mitogen doses. Addition of indomethacin to cultures of spleen cells from untreated donors induced greater increase of the lymphoproliferative response of cells from low responder B6 than from high responder C mice. The enhancing effect of indomethacin added in vitro was observed in cultures stimulated by optimal but not by supraoptimal doses of Con A. The addition of indomethacin did not enhance the response of B6 spleen lymphocytes depleted of adherent cells. Preincubation for 24 h prior to mitogen stimulation increased the response to high Con A doses of spleen cells from low responder B6 mice whereas this procedure did not enhance lymphocyte proliferation in cultures of spleen cells from high responder C mice. Supplementation with indomethacin in vitro combined with preincubation induced additive enhancing effects on DNA synthesis by B6 spleen lymphocytes, suggesting that each treatment acts through different mechanism(s). The results indicated that spleen cells from low responder B6 strain mice are more sensitive than cells from high responder C mice to the potentiating effect of indomethacin and preincubation on the proliferative response to Con A. These observations suggest that mechanisms sensitive to indomethacin and to preincubation contribute to the depression of mitogen induced DNA synthesis in low responder B6 mice.

Modulatory effect of zinc on the proliferative response of murine spleen cells to polyclonal T cell mitogens

To study the effect of zinc on the proliferative response to polyclonal T cell mitogens, spleen cells from C57BL/6 mice were cultured with or without ZnCl2 and stimulated with graded doses of concanavalin A or phytohemagglutinin. Addition of 10(-4) M ZnCl2 inhibited proliferation whereas 10(-5) to 10(-6) M ZnCl2 did not modify the response to suboptimal doses of mitogen but increased DNA synthesis in cultures stimulated with high doses of mitogen (10 or 20 micrograms/ml of concanavalin A and 10 or 25 microliters/ml of phytohemagglutinin) which are supraoptimal for C57BL/6 mice, and inhibited proliferation in cultures of spleen cells from animals of this strain, low responder to T cell mitogens. In contrast, supplementation with ZnCl2 did not enhance the response to mitogen of spleen cells from high responder BALB/c mice. The enhancing effects of ZnCl2 on the proliferative response of C57BL/6 cells were not observed following depletion of adherent cells or in cultures supplemented with 5 X 10(-5) M 2-mercaptoethanol, both conditions capable of abrogating the inhibitory effect of high mitogen doses on the response of C57BL/6 cells.

Ontogeny of T-cell mitogen response in Lewis rats. III. Juvenile adherent suppressor cells block adult mitogen responses

Spleen cells from suckling female Lewis rats (4 to 20 days old) were able to suppress mitogenic responses to concanavalin A (Con A) and phytohemagglutinin (PHA) of spleen or thymus cells from adult female Lewis rats and thymus cells from suckling Lewis rats. Thymus cells from suckling rats were unable to suppress adult spleen cell mitogenic responses to Con A. Removal of carbonyl iron (cFe)-, plastic-, or nylon-wool-adherent cells removed the suppressive action of juvenile spleen cells, but irradiation did not. Separated plastic-adherent spleen cells from suckling animals suppressed adult mitogenic responses to Con A. at optimal Con A doses 2-mercaptoethanol (2-ME, 2 X 10(-5) M) abolished the suppressive effect of juvenile cells, however, at the hyperoptimal dose of Con A (125 micrograms/ml) even higher doses of 2-ME did not relieve suppression by juvenile cells. These suppressor cells in suckling pups were affected by early weaning which decreased suppression, resulting in enhanced mitogenic responses of juvenile cells and removal of the ability to suppress adult mitogenic response.

Ontogeny of T-cell mitogen response in Lewis rats: II. Early appearance and loss of suppressor activity

Spleen cells from rats 2 to 132 days old were cultured with 1-125 micrograms/ml Concanavalin A (Con A). At high doses of Con A, the high spontaneous thymidine uptake of spleen cells from rats 15 to 21 days old was suppressed, whereas spleen cells from younger rats showed no suppression of spontaneous mitogenesis at equally high Con A doses. Removal of either plastic-, nylon wool-, or carbonyl iron (cFe) adherent cells not only removed suppression of background by high Con A doses, but also allowed mitogenic responses at adult levels in normally unresponsive 15 to 21 day old pups. Low doses of X-irradiation did not cause a similar loss of suppression. We suggest that although there is an influx of ConA responsive cells into the rat spleens at 15 to 16 days, the mitogen responses of these cells are suppressed by an adherent cell population which is activated by high doses of Con A.

Growth of rat-mouse hybridomas in nude mice and nude rats

Athymic (nude) mice and rats were inoculated intraperitoneally with rat-mouse hybridoma cells secreting monoclonal antibodies to rat MHC class I antigens in order to improve the yield of antibodies. Pristane priming and subsequent intraperitoneal injection of the hybridoma cells in to nude mice yielded ascites which contained antibody in high concentration (10-15 mg/ml). Complete Freund's adjuvant, mineral oil, pristane or antibody-antigen complexes were used to induce ascites in nude rats, but only pristane priming did so consistently. The hybridoma cells in the ascitic fluid failed to secrete antibody, although they contained intracellular antibody. However, when the pristane-primed nude rats received 250-500 rads of total body radiation prior to injection with the hybridoma cells, they produced large amounts of antibody. When the nude rats were splenectomized and injected with the hybridoma cells, they also produced antibody in high titers. There was no in vitro inhibition of antibody formation by the hybridoma cells cultured in medium containing 15% serum from nude rats, but co-culture of the hybridoma cells with splenic lymphocytes from normal or nude rats markedly inhibited antibody production. These results indicate that the defect in antibody secretion by the hybridoma cells in the ascites of nude rats is due to the presence of radiation-sensitive suppressor cells in the spleen.

Antigen-specific suppressor T lymphocytes in human lymphatic filariasis

Immune responses to parasite antigens are much lower in patients with microfilaremia than in persons with other manifestations of brugian filariasis. To determine whether hyporeactivity is associated with changes in populations of lymphocytes that regulate immune responses, we quantitated helper and suppressor T cells in the blood of patients infected with Brugia malayi. Increased numbers of suppressor T cells were present in 15 of 17 patients with microfilaremia and in six of 11 patients with elephantiasis. This increase correlated with hyporeactivity to filarial antigens but not to nonparasite antigens. Removal of suppressor T cells activated in vivo or in vitro improved reactivity to filarial antigens. These results suggest that immunosuppression induced by filarial parasites is a possible mechanism of survival of these organisms in an immunocompetent host.

A comparison of cell-mediated immunity and suppressor T-cell function in asthmatic and normal children

The role of general and suppressor T-cell function was investigated in a group of twelve children with atopic asthma and ten non-atopic control children. Studies of active E rosettes, lymphocyte stimulation, and delayed type skin responsiveness revealed no statistically significant group differences. Data obtained employing a concanavalin A-induced, suppressor T-cell assay revealed that the asthmatics generated significantly less suppressor cell activity than did the normal control group. There was no correlation between lack of suppressor cell function and serum IgE levels. The results of this study support the concept of suppressor T-cell dysfunction in atopic disease.

In vitro suppression of T-cell mitogenic response and tumor cell proliferation by spleen macrophages from normal chickens

Adherent cells isolated from spleen of normal specific pathogen-free chickens inhibited mitogen-induced blastogenesis of autochthonous, syngeneic, or allogeneic lymphocytes. The adherent cells were also inhibitory to in vitro proliferation of cells of a rapidly dividing tumor line, MDCC-MSB-1, derived from a lymphoma induced by Marek's disease virus. The effector cell of suppression of both lymphoprolifrative functions appeared to be a macrophage because the suppressive activity of adherent cells could be abrogated by pretreatment with carrageenan but not with antisera specific to chicken T or B cells. The proportion of macrophages needed for effective suppression was substantially higher than the proportion of macrophages ordinarily present in spleen of normal, unstimulated chickens. This heretofore unrecognized suppressive capability of normal, presumably resting macrophages have been detected in certain infections.

Influence of route of Mycobacterium lepraemurium injection on susceptibility to mouse leprosy and on lymphoblastic transformation

Groups of female C57BL/6 and C3H/St mice were inoculated intraperitoneally (i.p.) with 10(9), 10(7), and 10(5) bacilli and into the right hind footpad with 10(7) and 10(5) bacilli of Mycobacterium lepraemurium. The incidence of death from leprosy and the mean survival time of leprous mice were recorded. In addition, the blastogenic responses to the T-cell mitogens phytohemagglutinin and concanavalin A and to the B-cell mitogens lipopolysaccharide and dextran sulfate were evaluated at various times during the course of infection in the spleen and peripheral lymph nodes of mice infected with 10(7) bacilli. When M. lepraemurium was administered i.p., the two strains of mice succumbed to the disease at about the same time, except for the C57BL/6 mice infected with 10(9) bacilli, which died earlier than the C3H/St mice. Moreover, in both strains of mice, a progressive depression of blastogenesis, first to the T-cell mitogens and then to the B-cell mitogens in the spleen, and to the T-cell mitogens in the peripheral lymph nodes, occurred during the course of the infection, whereas the response to the B-cell mitogens in the nodes increased slowly during the advanced stage of the disease. When 10(7) and 10(5) bacilli were injected into the footpad, the C3H/St mice succumbed to the disease at 298 and 344 days, respectively, and the modifications of blastogenesis were similar to those observed in i.p.-infected C3H/St mice. In contrast, the C57BL/6 mice appeared resistant to footpad inoculation of M. lepraemurium, since they lived until the end of the observation period (466 days postinfection) and the depression of blastogenesis was not detectable until 1 year after the infection. Thus, it is concluded that for the C57BL/6 mice (but not for the C3H/St mice), the route of administration of M. lepraemurium can markedly influence the susceptibility or resistance to leprosy.

Regulatory influences on the response of rabbit T cells to concanavalin A and phytohaemagglutinin

The proliferative response, induced in rabbit spleen cells by concanavalin A (Con A) and phytohaemagglutinin (PHA), is abolished when T cells are killed with antibody against rabbit thymus lymphocyte antigen (RTLA) in the presence of complement. The response was examined with purified spleen T cells, to which various helper cell fractions were added; it could be shown that B cells help the responding T cells. The helper effect in the response to PHA is abolished and the response to Con A is reduced by any manoeuvre which destroys or removes B cells. Help by B cells is given when helper cells have lost proliferative capacity as a consequence of mitomycin-C treatment. Spleen cells adhering to the walls of culture tubes help suspended T spleen cells in their response to Con A. This help could be abolished by complement mediated cell kill with antibody to rabbit bursal equivalent lymphocyte antigen (RABELA). On the other hand, the helper effect in Con A response was increased when T cells were removed. Thus the response of T cells to Con A is regulated by helper B cells and suppressor T cells.