Suppression Of Lymphocyte Responses Research Articles

The Yin and Yang of the Bone Marrow Microenvironment: Pros and Cons of Mesenchymal Stromal Cells in Acute Myeloid Leukemia.

Mesenchymal stromal cells (MSCs) have, for a long time, been recognized as pivotal contributors in the set up and maintenance of the hematopoietic stem cell (HSC) niche, as well as in the development and differentiation of the lympho-hematopoietic system. MSCs also have a unique immunomodulatory capacity, which makes them able to affect, both in vitro and in vivo, the function of immune cells. These features, namely the facilitation of stem cell engraftment and the inhibition of lymphocyte responses, have both proven essential for successful allogeneic stem cell transplantation (allo-SCT), which remains the only curative option for several hematologic malignancies. For example, in steroid-refractory acute graft-vs. host disease developing after allo-SCT, MSCs have produced significant results and are now considered a treatment option. However, more recently, the other side of the MSC coin has been unveiled, because of their emerging role in creating a protective and immune-tolerant microenvironment able to support the survival of leukemic cells and affect the response to therapies. In this light, it has been proposed that the failure of current treatments to efficiently override the stroma-mediated protection of leukemic cells accounts for the high rate of relapse in acute myeloid leukemia, at least in part. In this review, we will focus on emerging microenvironment-driven mechanisms conferring a survival advantage to leukemic cells overt physiological HSCs. This body of evidence increasingly highlights the opportunity to consider tumor-microenvironment interactions when designing new therapeutic strategies.

Selective roles for toll-like receptors 2, 4, and 9 in systemic inflammation and immune dysfunction following peripheral tissue injury

Toll-like receptors (TLRs) detect endogenous ligands released after trauma and contribute to the proinflammatory response to injury. Posttraumatic mortality correlates with the extent of the immunoinflammatory response to injury that is composed of a complex regulation of innate and adaptive immune responses. Although TLRs are known to modulate innate immune responses, their role in the suppression of lymphocyte responses following traumatic tissue injury is unclear. This study used a murine model of severe peripheral tissue injury, involving muscle crush injury and injection of fracture components, to evaluate the roles of TLR2, TLR4, and TLR9 in the early and delayed immunoinflammatory phenotype. Posttraumatic immune dysfunction was measured in our trauma model using the following parameters: ex vivo splenocyte proliferation, TH1 cytokine release, and iNOS (inducible nitric oxide synthase) induction within splenic myeloid-derived suppressor cells. Systemic inflammation and liver damage were determined by circulating interleukin 6 levels and hepatocellular injury. Suppression of splenocyte responses after injury was dependent on TLR4 and TLR9 signaling as was posttraumatic iNOS upregulation in splenic myeloid-derived suppressor cells. TLR2 was found to have only a partial role through contribution to inhibition of splenocyte proliferation. This study also reveals the involvement of TLR2 and TLR4 in the initial systemic inflammatory response to traumatic tissue injury; however, this response was found to be TLR9 independent. These findings demonstrate the previously unidentified role of TLR2, TLR4, and TLR9 in the T cell-associated immune dysfunction following traumatic tissue injury. Importantly, this study also illustrates that TLRs play differing and selective roles in both the initial proinflammatory response and adaptive immune response after trauma. Furthermore, results in TLR9-deficient mice establish that the upregulation of early proinflammatory markers do not always correlate with the extent of sustained immune dysfunction. This suggests potential for targeted therapies that could limit immune dysfunction through selective inhibition of receptor function following injury.

Enhanced Susceptibility of the Immune System to Stress in Morphine-Tolerant Rats

The purpose of the present study was to determine the potential consequences to the immune system of the combined exposure of rats to stressor and morphine. Within 30 min following either morphine (5 mg/kg) injection or restraint stress (30 min) maximal analgesic responses as measured by tail-flick assay were observed. However, only morphine treatment was accompanied by a significant suppression (50%) in mitogen-stimulated lymphocyte proliferative responses. Restraint stress for either a 30-min or 2-h duration had no effect on lymphocyte responses. Exposure to a combination of restraint stress and acute morphine (5 mg/kg) resulted in a 50% suppression of lymphocyte responses which was similar in magnitude to that observed with morphine administration alone. When rats were injected twice daily for 4 days with increasing doses of morphine ranging from 10 mg/kg to 40 mg/kg, morphine (10 mg/kg) administration on Day 5 was not accompanied by either analgesia or depressed blood lymphocyte proliferative responses. These results indicated that tolerance had developed to both the analgesic and the immunosuppressive effects of morphine. However, upon exposure of morphine-tolerant animals to restraint stress, significant analgesic responses were retained. Furthermore, in contrast to the lack of suppression following restraint stress on lymphocyte responses in saline-injected animals, restraint for 30 min produced greater than a 70% suppression in morphine-tolerant animals. These data suggest that morphine tolerance may be accompanied by an enhanced susceptibility to the immunosuppressive effects of stress.

Mycoplasma bovis suppression of bovine lymphocyte response to phytohemagglutinin

The effect of viable Mycoplasma bovis on the in vitro bovine peripheral blood lymphocyte response to phytohemagglutinin (PHA) was studied. Results showed that M. bovis did not act as a mitogen for bovine lymphocytes. Viable M. bovis produced a dose and time dependent suppression of the PHA stimulated lymphocyte response. Suppression was not a result of differences in the viability of infected or control lymphocyte cultures. The suppressive effect of M. bovis was found to be independent of the concentration of PHA used in the test and the lymphocyte response could not be restored by supplementation of the culture medium with arginine. Delay for 48 h after PHA stimulation before adding M. bovis to the lymphocyte cultures diminished, but did not prevent, the suppression of the lymphocyte response. These results show that suppression of the lymphocyte response does not require the presence of M. bovis during the period of PHA stimulation, and that M. bovis was capable of interrupting [ 3H]-thymidine incorporation in lymphocytes which were actively synthesizing DNA.

Inhibition of lymphocyte responsiveness by a glial tumor cell-derived suppressive factor.

The results of this study demonstrate the presence of suppressive factor(s) in the tissue culture supernatants of cloned and freshly explanted malignant glioma cells. Culture supernatants obtained from these glial cell lines were demonstrated to have potent suppressive activity as evidenced by their ability to inhibit the proliferative response of normal human peripheral blood lymphocytes induced by phytohemagglutinin and anti-OKT3 monoclonal antibodies. The results further demonstrate the existence of a dose-response relationship between these supernatants and inhibition of mitogen-induced lymphocyte activation. Maximum production of suppressive activity by glial tumor cells was dependent on: 1) the number of tumor cells seeded in culture, 2) whether fetal calf serum was present, and 3) the duration of culture. The production of the suppressive factor(s) was not inhibited by the addition of inhibitors of prostaglandin E synthesis. Experiments designed to determine at what time during lymphocyte activation the suppressive factor was most effective demonstrated that the culture supernatants must be added during the first 24 hours of culture to exhibit inhibitory properties. Finally, proliferation of both the T-helper and T-suppressor/cytotoxic subsets was equally well inhibited by the glial tumor cell culture supernatants.

Role of CD2 and IL 1 beta in T cell responsiveness to IL 2.

We have evaluated the effects of an anti-CD2 monoclonal antibody (moAb), Leu-5b, on inhibition of lymphocyte responsiveness. Given previous reports that anti-CD2 moAb prevent production of interleukin 2 (IL 2), as well as up-regulation of IL 2 receptor, we chose a test system in which lymphocytes were activated by exogenously added recombinant IL 2 (rIL 2). Our studies thus allowed us to evaluate other possible mechanisms by which anti-CD2 moAb could act. We found that Leu-5b not only blocked the proliferative response of human peripheral blood leukocytes (PBL) to IL 2, but also the development of cytotoxicity as assayed in lectin-dependent cytotoxicity (LDCC). Addition of recombinant interleukin 1 beta (rIL 1 beta) reconstituted the proliferative response in the presence of Leu-5b but did not allow development of cytotoxicity. Our findings are consistent with the concept that Leu-5b delivers a signal to IL 2-responsive cells that prevents their subsequent proliferation and development of cytotoxicity, but that only the former event, i.e., proliferation, is reconstituted by the addition of IL 1 beta.

A linkage between the hemostatic and immune systems embodied in the fibrinolytic release of lymphocyte suppressive peptides.

Some cellular immune responses initiate the coagulation protease cascade and promote the formation of fibrin. Local fibrin deposition is requisite for the induration associated with delayed hypersensitivity reactions. The deposited fibrin also is catabolized. In the present study we demonstrate that plasmic cleavage of fibrinogen results in the generation of immunosuppressive activity in vitro that is not expressed by the intact molecule. This property is associated with small dialyzable peptides recovered from advanced plasmic digests of fibrinogen. The peptides inhibit phytohemagglutinin-, pokeweed mitogen-, and allogeneic cell-stimulated blastogenesis as well as proliferation in a dose-dependent fashion. The suppression of lymphocyte responses does not result from loss of cells or their viability. Suppression requires the presence of the peptides at the time of, or immediately after, the exposure of cells to the appropriate stimulus, and is manifest as both a delay and an absolute inhibition of [3H]thymidine uptake. Human peptides inhibit the response of murine spleen cells to mitogens, and B and T lymphocyte classes appear to be equally sensitive to suppression. Thymidine uptake by two continuous lymphoblastoid cell lines also is inhibited by the peptides, indicating a direct effect of the fibrinogen-derived peptides on lymphocytes. In contrast, the peptides stimulate thymidine uptake by a diploid fibroblast line, suggesting selectivity in the biologic effects of the peptides. These observations indicate that in addition to its primary role in hemostasis, the participation of fibrinogen and its derivative fibrin in inflammatory lesions includes the release of lymphocyte-suppressive peptides. This may play a role in regulation of the evolution of immunologic lesions in vivo.

Inhibition of lymphocyte response by prostaglandin-producing suppressor cells in patients with melanoma.

Peripheral blood mononuclear cells (PBMC) from 11 patients with metastatic melanoma (group II) had a significant decrease in blastogenesis to concanavalin A (Con A) (38.7 +/- 7.7 cpm X 10(3); mean +/- SE) compared to 21 patients who were disease free (70.6 +/- 6.7) or 16 healthy controls (83.6 +/- 10.3). If PBMC from patients were preincubated for 72 hr prior to exposure to mitogen, blastogenesis was restored to normal. In group II patients a similar improvement in reactivity of fresh PBMC occurred with indomethacin addition or following rigorous depletion of adherent monocytes. Supernatants from cells cultured with and without Con A in several group II patients contained very high levels of endogenous PGE2. Patients had a greater percentage of T lymphocytes bearing Fc receptors for ox erythrocytes (T gamma) than controls, which appeared to correlate with the increased sensitivity to suppression by exogenously added PGE2. These data suggest that the decreased blastogenesis in certain melanoma patients is due to an increase in PGE2 production by monocytes, along with an increase in lymphocyte sensitivity to its effects.

Suppression of lymphocyte responses by Actinobacillus actinomycetemcomitans.

Suppression of lymphocyte responses by Actinobacillus actinomycetemcomitans.

Suppression of Lymphocyte Responses by Monocytes With Untreated and Treated Multiple Myeloma

Abstract Studies were performed on 15 untreated and 14 treated patients with multiple myeloma. The monocyte content was normal in blood but elevated in mononuclear leukocytes (MNL) from treated but not untreated patients (p less than 0.001). This correlated with the severity of lymphopenia in blood (p less than 0.01). Three patterns of immunoglobulin(Ig) synthesis emerged. (1) Most untreated patients showed normal polyclonal responses to pokeweek mitogen. (2) Of 12 treated patients, the 8 whose MNL included greater than 30% monocytes had subnormal Ig responses to pokeweek mitogen. Ig synthesis increased when adherent cells that suppressed Ig synthesis were depleted. Suppression in vitro bore no relationship to polyclonal immunoglobulin levels in serum. (3) Three patients had early blood invasion by plasmacytoid cells. Their MNL spontaneously released large amounts of the Ig class of their serum gammopathies. Proliferative responses to phytohemagglutinin by MNL from all patients were reduced, in part due to monocytoid cell suppression and in part to intrinsic T-cell hyporesponsiveness. B- and T-cell responses in vitro are sometimes suppressed with myeloma. This is related to elevated monocyte percentages in MNL preparations. This excess of monocytes is a function of lymphopenia secondary to therapy, rather than the primary malignant process itself. No evidence was found that suppression by monocytes is qualitatively altered by myeloma or its treatment.

Suppression of lymphocyte responses by monocytes with untreated and treated multiple myeloma

Studies were performed on 15 untreated and 14 treated patients with multiple myeloma. The monocyte content was normal in blood but elevated in mononuclear leukocytes (MNL) from treated but not untreated patients (p less than 0.001). This correlated with the severity of lymphopenia in blood (p less than 0.01). Three patterns of immunoglobulin(Ig) synthesis emerged. (1) Most untreated patients showed normal polyclonal responses to pokeweek mitogen. (2) Of 12 treated patients, the 8 whose MNL included greater than 30% monocytes had subnormal Ig responses to pokeweek mitogen. Ig synthesis increased when adherent cells that suppressed Ig synthesis were depleted. Suppression in vitro bore no relationship to polyclonal immunoglobulin levels in serum. (3) Three patients had early blood invasion by plasmacytoid cells. Their MNL spontaneously released large amounts of the Ig class of their serum gammopathies. Proliferative responses to phytohemagglutinin by MNL from all patients were reduced, in part due to monocytoid cell suppression and in part to intrinsic T-cell hyporesponsiveness. B- and T-cell responses in vitro are sometimes suppressed with myeloma. This is related to elevated monocyte percentages in MNL preparations. This excess of monocytes is a function of lymphopenia secondary to therapy, rather than the primary malignant process itself. No evidence was found that suppression by monocytes is qualitatively altered by myeloma or its treatment.

Inhibition of mitogen-induced human lymphocyte responsiveness by polymixin antibiotics.

Polymixin antibiotics, polymixin B and polymixin E (colistin) inhibited the mitogen-induced lymphoproliferative response of human lymphocytes. Inhibition of the lymphocyte response to PHA, PWM and Con A was evident at a low concentration of 1 U/ml of antibiotics. Lymphocytes in which the signals for proliferation had occurred were similarly prevented from proliferating. The effects were not due to cell death (toxicity). Since polymixin concentrations at which inhibition of lymphocyte proliferation was observed are employed in tissue culture medium and are also attained in plasma of patients, the results suggest that the use of the antibiotics in lymphocyte cultures limits lymphocyte responsiveness and that patients receiving polymixin antibiotics may experience a state of immunosuppression.

Suppression of lymphocyte responses by monocytoid cells does not require cell-cell contact

High numbers of mononuclear leukocytes (MNL) in one compartment of a diffusion chamber profoundly suppressed lymphocyte responses in the other compartment. Suppression was expressed by decreased incorporation of labeled thymidine, uridine, and leucine and lowered blastogenesis in T-lymphoproliferative cultures as well as reduced Ig synthesis. The inhibitory effect, which was reversible, was experienced predominantly during the later stages of the culture period. Suppression of both autologous and allogeneic effector cells was associated with a radioresistant, moderately adherent non-T-cell subpopulation that did not require activation. Cell contact was not required suggesting that suppression was related to release of a mediator. This mediator was of low molecular weight and was remarkably labile. Only a portion of this modulation could be ascribed to prostaglandins and none to products of the lipoxygenase pathway, hydrogen peroxide, or the accumulation of thymidine.

Suppression of lymphocyte responses by cephalosporins

Human peripheral blood lymphocytes were cultured in several concentrations of each of several cephalosporins. Responses to phytohemagglutinin were compared with that of duplicate cultures containing penicillin-streptomycin, chloramphenicol, or no antibiotics. Possible effects of cephalosporins on responses of lymphocytes to concanavalin A and pokeweed mitogen were similarly determined. Significant suppression of responses to phytohemagglutinin and concanavalin A were seen in cultures containing 50 microgram each of cephalothin, cephalexin, or cephradine per ml. Lymphocyte responses to pokeweed mitogen were suppressed by 50 microgram of cephalexin, cephradine, or cefoxitin per ml. A higher concentration (100 microgram/ml) of all cephalosporins except cefoxitin and cefazolin suppressed the phytohemagglutinin response to less than 20% that of controls. Chloramphenicol (50 microgram/ml) did not inhibit the response to any mitogen used. These findings suggest that cephalosporins should not be used for prevention of bacterial overgrowth in certain cell cultures. Since many of the cephalosporins were suppressive in therapeutically attainable concentrations, these results may have potential clinical significance.

Clinical drug dfficacy and in vitro inhibition of lymphocyte responses in rheumatoid arthritis

Clinical drug dfficacy and in vitro inhibition of lymphocyte responses in rheumatoid arthritis