How do immunomodulators affect host defense in the burn patient?

In vitro induction of anti-type 2 T cells by glycyrrhizin

Glycyrrhizin (GR), an active component of licorice roots, has been previously shown to induce the generation of anti-type 2 T cells (anti-BI2T cells), which are able to counteract the activity of burn-induced CD8+ type 2 T cells (BI2T cells), in thermally injured and normal mice. In the present study, anti-BI2T cells were generated in vitro in cultures of spleen cells stimulated with GR. Anti-BI2T cells were induced in vitro when splenic mononuclear cells (SMNC) were stimulated in vitro for 24 to 72 h with 0.1-10 micrograms/ml of GR. Anti-BI2T cell activity was detected when suppressor macrophages (M phi) were depleted from SMNC after stimulation with GR. However, the GR-stimulated generation of anti-BI2T cells required the participation of M phi or their sonicated fractions. Anti-BI2T cells induced in vitro by GR were identified as Vicia villosa lectin adherent IFN7 producing-CD4+ T cells lacking the ability to produce IL-2, IL-4 or IL-10. These results indicate that anti-BI2T cells are generated by GR in vitro. M phi are not only necessary for the generation of anti-BI2T cells induced by GR but also inhibit their activity.

Inhibition of burn-associated suppressor cell generation by glycyrrhizin through the induction of contrasuppressor T cells

The inhibitory effect of glycyrrhizin (GR), an anti-inflammatory Chinese herbal drug extracted from licorice roots, on the generation of suppressor T cells in thermally injured mice (TI-mice) was investigated. The burn-associated suppressor T cell (BTs cell) activity was demonstrated in splenic mononuclear cells (SMNC) from mice 2 to 8 days after thermal injury when suppressor cell activity was assayed in a one-way mixed lymphocyte reaction. However, when TI-mice were treated with GR, SMNC harvested 6 days after thermal injury showed no suppressor cell activity. This activity of GR demonstrated a dose-response effect, with a dose of 10 mg/kg exhibiting peak levels of the activity. Since GR had no direct inactivating activities against BTs cells in vitro, the inhibitory effect of SMNC, derived from TI-mice treated with GR, on the activity of BTs cells was examined in the same mixed lymphocyte reaction system, and the results showed that the SMNC from GR-treated mice 6 days after thermal injury counteracted the activity of BTs cells. The type of cell responsible for this inhibition of BTs cell activities was a CD3+, L3T4+, Vicia villosa lectin-adherent T cell with the same phenotypic properties previously exhibited by contrasuppressor cells. These results suggest that GR may regulate the generation of BTs cells through the induction of contrasuppressor cells. Since there are many reports describing septic infections due to the appearance of BTs cells in postburn patients, it may be possible to apply GR or blood preparations containing contrasuppressor cell populations induced by GR in healthy volunteers into immunosuppressed burn patients to avoid infections.

Splenocyte blastogenesis suppressed in rats implanted with an osmotic pump

Rats implanted subcutaneously with an empty osmotic pump connected by a polyethylene catheter to a jugular vein for 5 to 10 days evinced a decreased splenocyte responsiveness to blastogenic stimulation in vitro to bacterial lipopolysaccharide, a known B cell stimulator, as well as to the plant mitogens pokeweed mitogen (PWM), a known stimulator of T and B cells, and Concanavilan A, a known T cell stimulator. The surface of the implanted pumps became infiltrated with lymphoid cells, especially macrophages. Suppression of blastogenic responsiveness after implantation for 10 days with an empty pump or even a pump dispensing pyrogen free saline only in a continuous manner was nearly as marked as that which occurred at 2-5 days after continuous infusion with endotoxin. These depressed blastogenic responses, although less, were also evident when rats were implanted with a catheter into a jugular vein connected by means of a swivel to either an empty pump or one dispensing pyrogen free saline. Suppression of blastogenic responsiveness was not related to alteration in serum complement or corticosteroid levels. Since administration of immunomodulatory substances systemically to individuals often involves implantation of an osmotic pump, investigation into the mechanisms of lymphoid cell suppression associated with an implanted pump itself has potential significance.

Effect of an immunomodulating agent, RU 414740, on polymorphonuclear responsiveness after burn injury

An impairment of polymorphonuclear leukocyte (PMN) functions has been described following burn trauma. It was thus of interest to investigate the effect of RU 41740, an agent known to stimulate these cells, on rat PMN functions after burn injury. In the present study the responsiveness to classical stimuli of PMN from untreated burned rats was approximately 40% lower than healthy control values. In vitro treatment with RU 41740 increased oxidative metabolism of PMNs from burned and healthy rats. The effect was dose-related but was most striking in the case of PMNs from healthy rats. Significant differences were obtained with concentrations higher than 1 micrograms/ml for healthy rats but only 10 micrograms/ml for burned rats. In vivo treatment with RU 41740 also led to an enhancement of PMN oxidative metabolism on both burned and healthy rats. The maximal effective dose was 10 mg/kg/day in both cases. In contrast, 25 and 50 mg/kg/day doses inhibited PMN oxidative metabolism.

Kinetics of interleukin-2 and interleukin-6 synthesis following major mechanical trauma

Although it is known that mitogen-induced lymphocyte proliferation and interleukin-2 (IL-2) synthesis are depressed following mechanical trauma, it is not known whether these defects are due to high levels of circulating prostaglandin E2 released by macrophages, suppressor T-lymphocytes, and serum suppressive factors or due to intracellular defects in T-lymphocytes. Moreover, the kinetic of interleukin-6 (IL-6), a new multifunctional cytokine, following trauma is not known. To study this, highly purified T-cell cultures were prepared from 21 patients with major mechanical trauma on Days 3, 7, 10, 14, and 21 post-trauma and assayed for proliferative response to phytohemagglutinin, IL-2, and IL-6 synthesis. T-lymphocyte proliferation of patients was unaltered on all days post-trauma compared to that of healthy controls. Interleukin-2 synthesis of patients showed a significant (P less than 0.01) reduction ranging from 23% of control values on Day 3 to 40% on Day 21. Interleukin-6 synthesis in contrast was markedly increased (P less than 0.05) in the patient group on all days up to sixfold (Day 3) with a tendency toward normalization on Day 21. High levels of IL-6 correlated with the appearance of infectious complications in the post-traumatic course. These data indicate that the alterations in T-cell proliferation and IL-2 synthesis following major injury found in earlier studies are caused by different suppressor mechanisms. While T-cell proliferation is only decreased by extracellular components, IL-2 synthesis is suppressed mainly by an intracellular defect. The role of highly increased IL-6 levels and its effect on the immune response are so far unknown.

Alterations of the host defense mechanism in burned patients

The host defense mechanism against microbial infection is seriously suppressed following a major thermal injury. In this article the specific and nonspecific systems are dissected, demonstrating known sites of alteration, and laying out a rational groundwork for future intervention.