Immunoregulatory Potential Research Articles

Serum interleukin-2 receptor as a possible mediator of immunosuppression after burn injury.

Concentrations of the interleukin-2 receptor are significantly elevated in serum after burn injury. To examine the immunoregulatory potential of this molecule, suppressive activity of sera from patients with major burns (n = 16; 40% to 80% total body surface area) was assessed before and after immunoaffinity adsorption with interleukin-2. The preadsorption level of interleukin-2 receptor in the pooled serum after burn injury was 6250 U/ml. This serum demonstrated a strong suppressive activity, inhibiting expression of cellular interleukin-2 receptor and proliferative responses of normal human lymphocytes to alloantigen and exogenous interleukin-2 by 60% to 90%. Adsorption of pooled serum after burn injury with interleukin-2 lowered the level of interleukin-2 receptor to 1800 U/ml and reduced its immunosuppressive activity. The percentage of interleukin-2 receptor-bearing cells, and cell proliferative responses, increased by 50% to 70% compared with sham adsorbed pooled serum after burn injury. Thus serum interleukin-2 receptor after burn injury may represent a specific mediator for downregulation of interleukin-2-dependent responses.

Systemic uptake and intestinal inflammatory effects of luminal bacterial cell wall polymers in rats with acute colonic injury.

The systemic uptake and local intestinal inflammatory potential of luminal bacterial cell wall polymers in rats with normal and acutely inflamed colons were measured. Rats were injected intracecally with either 125I-labeled group A streptococcal peptidoglycan-polysaccharide complexes or equal amounts of Na125I, after either nonspecific colonic injury with 4% acetic acid or injection with buffer. The colons of rats injected with peptidoglycan-polysaccharide had higher inflammatory scores than Na125I-injected rats, a greater incidence of mucosal ulceration and transmural inflammation after acetic acid injury, and an increased frequency of focal accumulations of inflammatory cells in the lamina propria and submucosa after buffer injection. Radioactivity in the liver, spleen, and mesenteric lymph nodes was higher in the colon-injured rats that received peptidoglycan-polysaccharide 48 h before tissue collection than in the noninjured rats (P less than 0.002). Group A streptococcal polysaccharide antigen concentration within the liver, spleen, and mesenteric lymph nodes, measured by enzyme-linked immunosorbent assay, was significantly higher in the colon-injured rats that received cell wall polymers than in noninjured rats. These results indicate that luminal bacterial cell wall polymers with well-described inflammatory and immunoregulatory potential can cross injured colonic epithelia and are capable of initiating and potentiating intestinal inflammation.

Human milk-derived lactoferrin inhibits mitogen and alloantigen induced human lymphocyte proliferation

Purified lactoferrin (LF), isolated from human milk, was tested for its effect on human T-lymphocyte proliferative responses to phytohemagglutinin (PHA) and to alloantigens in mixed lymphocyte culture. LF inhibited proliferation in both assays in a dose-dependent manner. The suppressive effect was not due to LF mediated cytotoxicity since washing cells that had been pre-incubated with LF restored their proliferative activity. LF was most effective in suppressing the PHA response when added within 24 h of culture initiation. Iron saturated LF failed to inhibit PHA-induced proliferation, suggesting that the mechanisms of suppression involve the chelating property of LF. The suppressive effect of LF on T-lymphocyte proliferative response in vitro supports the notion that LF has significant immunoregulatory potential in vivo.

An autoreactive T cell clone that can be activated to provide both helper and suppressor function.

To understand further the biologic significance of the autologous mixed lymphocyte reaction, we determined the functional properties of autoreactive T cell lines and clones. Initially, we found that cells in an uncloned autoreactive Leu-3+ T cell line helped immunoglobulin production when added to cultures containing fresh T and non-T cells in the absence of pokeweed mitogen (PWM) but suppressed immunoglobulin production in the same cultures in the presence of PWM. To explain this phenomenon, we studied the immunoregulatory potential of an autoreactive T cell clone termed MTC-4. This clone bore the phenotype Leu-3+, 2-, 8-, 11-, DR+ and underwent proliferation when co-cultured with autologous, but not allogeneic non-T cells. Of interest, the immunoregulatory potential of the MTC-4 cells varied according to how the cells were activated. When MTC-4 cells were cultured with autologous non-T cells in the absence of antigen or mitogen (unactivated non-T cells), polyclonal immunoglobulin production (detected by reverse PFC assay) was observed. This helper activity was MHC-restricted in that it was elicited only by autologous non-T cells or MHC-matched allogeneic non-T cells; however, once activated by autologous non-T cells, it could also help allogeneic non-T cells. In contrast, when MTC-4 cells were cultured with autologous non-T cells in the presence of PWM (activated non-T cells), immunoglobulin production was greatly suppressed. This suppression was also observed when MTC-4 cells were added to cultures containing exogenous T cell help (such as that provided by autologous fresh T cells) and was not due to a direct effect of PWM on the T cell clone, because preincubation of MTC-4 cells with PWM before culture with non-T cells did not result in suppression. On the basis of these data, we conclude that autoreactive T cells can have dual immunoregulatory function that is manifest, at least in part, at the single cell level. Moreover, these regulatory functions are differentially elicited depending on the state of activation of the stimulating autologous non-T cells: when stimulated by MHC antigens present on unactivated B cells, they provide helper activity; and when stimulated by MHC antigens present on activated B cells, they act as suppressor cells. Autoreactive T cells with dual regulatory potential appear to make up a substantial proportion of all autoreactive T cells and are cells that are uniquely adapted to maintain immunologic homeostasis.

Macrophage activation: priming activity from a T-cell hybridoma is attributable to interferon-gamma.

Antiviral and macrophage-priming activities in the supernatant medium of a subclone of a concanavalin A-stimulated mouse T-cell hybridoma were investigated. The two activities were associated with a molecular weight of approximately 50,000 and could not be separated by various approaches. Both activities were eliminated by a highly specific neutralizing antibody against mouse interferon-gamma, but not by antibody against interferon-alpha and -beta. The ratio of priming to antiviral activity in the hybridoma culture supernate was indistinguishable from the ratio obtained with mouse interferon-gamma prepared by recombinant DNA technology. It was concluded from these data that the priming activity in hybridoma culture supernates was attributable to interferon-gamma and that this mediator is one form of the lymphokine macrophage-activating factor. Interferon-gamma was greater than 800 times more efficient at priming mouse macrophages for tumor cell killing than was a mixture of interferon-alpha and -beta. This finding contributes to growing awareness that type II interferon may have greater immunoregulatory potential than type I interferons.

Immunoglobulin secretion in the human autologous mixed leukocyte reaction. Definition of a suppressor-amplifier circuit using monoclonal antibodies.

The induction of immunoglobulin (Ig) synthesis in the autologous MLR has an absolute requirement for helper/inducer (Leu-3) T cells, whereas an excess of suppressor/cytotoxic (leu-2) cells suppresses the response. The current study was an effort to assess the immunoregulatory potential to T cells activated in the autologous mixed-leukocyte response (MLR). T cells were cultured with autologous non-T cells for 8-9 d, after which the activated T cells were fractionated into subsets with monoclonal antibodies to T cell markers and HLA-DR antigen. Each population was co-cultured in fresh autologous MLR, and on the 8th day of culture, Ig-secreting cells were measured in a reverse hemolytic plaque assay. The results show that activated Leu-2, DR+ T cells, but neither Leu-2, DR- nor Leu-3 T cells, were at least 50 times more potent as suppressors of IgM and IgG synthesis than fresh Leu-2 cells alone. The activation of this Leu-2, DR+ subpopulation required Leu-3 cells in the primary culture. Furthermore, in the absence of Leu-2 cells in the second culture, little or no suppression was observed, suggesting that the Leu-2, DR+ cells act to amplify or induce suppressor effects of fresh Leu-2 cells. This indicates that at least two distinct subpopulations of Leu-2 cells are required for maximal suppression of an immune response, and that immunoregulatory circuits analogous to those described in the mouse exist in man.

Heterogeneity of tumorigenicity phenotype in murine tumors. I. Characterization of regressor and progressor clones isolated from a nonmutagenized ultraviolet regressor tumor

We have shown that both regressor and progressor clones can be isolated from a UV regressor tumor, RD-1024. Although the daughter clones are characterized by differences in tumorigenic potential in normal transplant hosts, they nevertheless seem to express the same major tumor rejection antigens, because immunization with either the regressor parent tumor, RD-1024, or with regressor Cl 8 protects against subsequent challenge with progressor C1 4 or Cl 9. Consistent with the in vivo-generated data is the evidence that draining lymph node cells with functional specificity for regressor Cl 8 are capable of cross-reactive cytotoxicity in an in vitro chromium release assay. We have demonstrated an indirect interaction occurring in vivo between regressor and progressor cells, in that Cl 8 cells have the ability to influence the outcome of simultaneous or sequential challenge with Cl 4 or Cl 9 cells. Because 500 rad of gamma irradiation has been shown to compromise the ability of mice to respond to a primary challenge with tumor, an immunological mechanism is implicated in the ultimate rejection of progressor tumor in a doubly challenged host. The importance of these results lies in the knowledge that these interacting subpopulations have been isolated directly from a tumor growing in vivo and that no selection pressure has been exerted on the cells greater than the short in vitro culture period necessary for the isolation and expansion of individual clones. The apparent immunoregulatory potential in a tumor-bearing animal is thus seen to be modified in accordance with the phenotypic heterogeneity of the cells within that tumor.

Suppressor cell regulation of cell-mediated immune responses in renal infection in vitro modulation of suppressor cell activity.

Infection-induced anergy is a frequent complication of bacterial, viral, and parsitic infection. A marked suppression of the thymus-derived (T) lymphocyte response to concanavalin A has been demonstrated in vitro during renal infection and the mechanisms by which suppression occurs have been investigated. In particular we have considered the possibility that suppression might result from the inhibitory effect of prostaglandins, secreted by activated macrophages with immunoregulatory potential. The experiments have shown that the T-lymphocyte effector status in experimentally-induced renal infection is determined by two suppressor cells, one infection-induced and the other naturally occurring. The inability to respond to mitogenic stimulation was reversible and restoration of immune responsiveness to splenic lymphocytes from infected animals could be achieved in two stepwise manipulations; differential centrifugation removed the infection-induced suppressor cells, and the suppressor activity of the naturally occurring suppressor cells could then be inhibited by indomethacin. Thus the two suppressor cells were distinguishable on the basis of their physical characteristics and their response to indomethacin. The dominant factor determining the immune responsiveness of splenic lymphocytes from the pyelonephritic animals was, however, the infection-induced suppressor cell. This cell has been characterized as a sedimentable cell (30 g) with suppressor activity demonstrable in co-culture experiments. Plastic-adherent cells from the sedimentable fraction of pyelonephritic animals' splenic cells were shown to have suppressor activity that was not inhibited by indomethacin. The infection-induced and naturally occurring suppressor cells can be viewed as prototypes for the equivalent cells in man and may be useful models for studying the role of these cells as determinants in the pathogenesis of infectious disease.

Modification of in vitro and in vivo immune function by acute inflammatory cells.

The ability of adoptively transferred, syngeneic polymorphonuclear leukocyte-rich (PMNLr) inflammatory cells to influence lymphocyte-mediated cytotoxicity (LMC), complement-dependent cytotoxicity (CDC), and skin allograft survival was studied in a murine model. BALB/c mouse PMNLr, stimulated by i.p. injection of either glycogen (G/PMNLr) or thioglycollate (T/PMNLr), were transferred to other BALB/c mice at the time of primary or secondary immunization with a cellular alloantigen (C57BL/6 spleen cells) or after skin allografting (C57BL/6 tailskin). The metabolic activity of each PMNLr population was determined by measuring glucose utilization in the hexose monophosphate shunt. It appeared that metabolic activity of the T/PMNLr was significantly greater than that of the G/PMNLr. Our results indicate that, while the infusion of G/PMNLr tended to suppress the primary cell-mediated immune response and the secondary humoral immune response, the infusion of T/PMNLr stimulated both of these responses. Furthermore, i.p. infusion of mice with G/PMNLr at a time approximating grafting resulted in prolonged graft survival, but neither T/PMNLr nor syngeneic thymocytes effect graft survival. Our data demonstrate that both cellular and humoral immunity can be modified by acute inflammatory cells. The metabolic status of the acute inflammatory cells seems to be critical in determining their immunoregulatory potential.