Recombinant interleukin-2 (rIL-2) improves immune response and host resistance to septic challenge in thermally injured mice.

Impaired immune competence leading to decreased resistance to sepsis is a major cause of death in burn patients. We have previously shown that increased mortality from a septic challenge correlated with impaired splenocyte interleukin-2 (IL-2) production and response to T cell mitogens in mice subjected to a 25% surface area scald burn. We report now that the addition of recombinant (r) IL-2 (100 U/ml) in vitro to splenocytes from burned animals restored mitogen responses to normal. Burned mice intraperitoneally received 16,000 U of rIL-2 (selected on the basis of dose-response experiments) once daily in 0.5 ml 5% dextrose (5% D) on days 1 through 6 after thermal injury and were compared with burned mice treated with only 5% D. Both groups were subjected to cecal ligation and puncture 10 days after burn; 4 days later, there were no survivors in the 5% D group, whereas 45% of the rIL-2 group remained alive (p = 0.001; Gehan statistic). We found that rIL-2 treatment at the dose selected resulted in no apparent toxicity in burned mice. Finally, splenocytes from rIL-2-treated burned mice showed improved responses to T cell mitogens in vitro compared with 5% D-treated controls. We conclude that rIL-2 therapy may have a role in the restoration of immune competence after thermal injury.

Temporal correlation of impaired immune response after thermal injury with susceptibility to infection in a murine model.

Suppression of cellular immunity and increased susceptibility to sepsis frequently accompany thermal injury. However, a convincing association between the two has been difficult to establish in human beings. Therefore we chose to investigate the relationship of impaired cell-mediated immunity with susceptibility to sepsis in an animal model. We studied the response to phytohemagglutinin (PHA) and interleukin-2 (IL-2) production by splenocytes from mice subjected to a standard 25% scald burn and killed at intervals of 3, 5, 7, 10, 14, and 25 days after thermal injury. Burned mice were compared in all instances to sham-burn animals (i.e., animals that had been anesthetized and shaved but not burned). We also studied mortality after cecal ligation and puncture (CLP), as a septic challenge, in burned and control animals at the same postburn intervals. We found maximal suppression (50% to 55%) of the PHA response at 10 to 14 days after injury and maximum suppression (68%) of IL-2 production at 7 days. Both of these parameters returned to normal by postinjury day 28. Mortality after CLP increased gradually from control levels after thermal injury up to a maximum of 88% on postburn day 10 and also returned to control levels after 28 days after burn. Significant correlations were found between mortality after CLP in the postburn period and suppression of the PHA response, on the one hand, and the suppression of IL-2 production, on the other (r = 0.89 and 0.91, respectively; p less than 0.05). This result implies a causal relationship between impaired cell-mediated immunity and susceptibility to sepsis after burn injury.

Mechanisms of immunosuppression associated with severe nonthermal traumatic injuries in man: production of interleukin 1 and 2.

Depression of cell-mediated immunity in patients following severe traumatic injury has been well documented in vitro and in vivo. However, the exact mechanism of this defect is still controversial. In this study, we have investigated the ability of injured patients' peripheral blood mononuclear cells (PBMC) to produce two important immunoregulatory molecules, interleukin 1 (IL 1) and interleukin 2 (IL 2). Eighteen traumatic injury patients were studied during the course of their hospital stay and their results compared with a group of 18 normal age- and sex-matched controls. The results showed the following. (1) Production of IL 2 by normal PBMC in response to optimal doses of mitogen may vary with sex as well as age. (2) Adherent mononuclear cells from trauma patients produced at least as much IL 1 as normals. (3) IL 2 production, however, was markedly suppressed (normals, 1.6 +/- 0.2 U; traumatic injury, 0.6 +/- 0.1 U; P = 0.001) and persisted for as long as 50 days postinjury. OKT4+ cells were not significantly decreased at any time, nor were OKT8+ suppressor/cytotoxic cells increased at any time. Decreased IL 2 production in patients treated with steroids or those who were septic was not different from that in those patients who were not treated with steroids or were not septic. These results suggest that the cause of the defect in IL 2 production in traumatic injury patients is not related to a lack of the IL 1 signal, producer T cells, or Ia+ monocytes or to increased suppressor T cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of in vivo endotoxin infusions on in vitro cellular immune responses in humans.

Studies of the immune response of patients following major injury have identified significant abnormalities, some of which may be due to the effects of endotoxin. To evaluate the effect of endotoxin on the immune system without conflicting variables, we studied 18 normal, healthy male volunteers each on two occasions. In one study, Escherichia coli endotoxin was administered intravenously at a dose of 4 ng/kg. In the other, saline was given. Blood for immune function studies was obtained at either 0, 4, or 24 hr (seven volunteers), 0, 1, and 4 hr (five volunteers), or 0, 4, and 6 hr (six volunteers) postinfusion. Peripheral blood mononuclear cells (PBMC) were isolated and adjusted to the same concentration. Measurements following endotoxin infusion were compared with those of the same volunteers following saline infusion and with those from normal ambulatory laboratory volunteers. Interleukin 1 (IL-1) production by adherent cells was significantly reduced at 1 hr post endotoxin infusion. Significant decreases in number of mononuclear cells, response to phytohemagglutinin (PHA), and production of IL-2 and IL-1 were observed by 4 hr after endotoxin infusion. No significant changes in percentages of monocytes, lymphocytes, or CD3, CD4, or CD8 lymphocytes were observed at any time. By 24 hr postinfusion all values had returned to normal or, in some cases, supranormal levels. Response to PHA by PBMC from volunteers 4 hr following endotoxin was completely restored by in vitro addition of recombinant human IL-2 but was only marginally improved by IL-1. In vitro addition of indomethacin to PBMC cultures responding to PHA reduced the suppression observed after in vivo endotoxin but also was not as effective as IL-2. In a fourth study, seven volunteers were treated as above either with two doses (800 mg each) of the cyclooxygenase inhibitor ibuprofen before endotoxin infusion or with ibuprofen alone. Ibuprofen pretreatment completely restored the PBMC response to PHA to normal and caused a significant decrease in the endotoxin-induced suppression of IL-2 production. However, the decrease in circulating PBMC number and adherent cell secretion of IL-1 was not affected by inhibition of the cyclooxygenase pathway. These results suggest that endotoxin has immunomodulatory effects on both adherent mononuclear-cell and T-lymphocyte function and that more than one mechanism is involved.