Influence of burn-induced lipid-protein complex on IL2 secretion by PBMC in vitro

Burn injury induces a change in T cell homeostasis affecting preferentially CD4+T cells

Burn injuries are known to be associated with altered immune functions, resulting in decreased resistance to subsequent infection. In the present study, we determined the in vivo changes in T cell homeostasis following burn injury. Two groups of mice were used: a sham-burn group receiving buprenorphine as an analgesic and a burn group receiving buprenorphine and subjected to burn injury on 20% of the total body surface area. Results showed an important decrease in splenocytes following burn injury. This decrease persisted for 5 days and was followed, at day 10, by a 63% increase in number of cells. In vivo cell proliferation, as determined by the incorporation of 5-bromo-2'-dexoxyuridine, showed a significant increase of cycling splenocytes between days 2 and 10 after burn injury. The percentage of CD4+ and CD8+ T cells in the spleen was altered for 10 days after thermal injury. Analysis of naive (CD62Lhigh CD44low) and effector/memory (CD62Llow CD44high) T cells showed a percent decrease, independent of the expression of CD4 or CD8 molecules. However, early activation markers, such as CD69+, were expressed only on CD4+ T cells after a number of days following injury. Even with an activated phenotype, 10 days post-burn injury, CD4+ naive T cells significantly increased spontaneous apoptosis, detected by using a fluorescent DNA-binding agent 7-amino-actinomycin D. CD8+ T lymphocytes did not express early activation markers and were more resistant to apoptosis. Using purified T cells, we have shown unresponsiveness at day 10. Overall, these results demonstrate that mechanisms of T cell homeostasis were perturbed following burn injury. However, after 10 days, this perturbation persisted only in CD4+ T cells.

Skin toxicity induced by wet heat

Pieces of human skin from the skin bank were heated in an autoclave for 1 or 5 min at temperatures 80, 90, 100, 110 and 135 degrees C. The pieces were then homogenized and the homogenates were injected intraperitoneally into groups of mice. The amount injected was either a quantity equivalent to 50 or 75% of the mouse body surface area. Fourteen separate experiments were carried out, each one with a variety of temperatures. Mortality in the groups of mice was recorded by the 8th day. Control mice received homogenates of skin heated to no more that 38 degrees C and out of a total of 104 control mice there were only 4 deaths. In contrast homogenates of skin heated to 135 degrees C killed from 80 to 100% of the mice in different groups, averaging 92%. Skin heated to 110 degrees C killed from 33 to 90% of the mice in different groups, averaging 63%. Skin heated to 100 degrees C killed from 0 to 80% of the mice in different groups, averaging 33%. Temperatures of 80 and 90 degrees C killed no more than 10% of the mice in any group, averaging less than 3%. One minute of heating seemed to be sufficient to induce the toxic effect in the skin. These findings indicated that wet heat application to skin was capable of inducing toxicity in a fashion similar to that demonstrated many years ago with hotter dry temperatures applied to skin for 15s. That application was shown to induce polymerization of skin cell membrane lipid proteins rendering them toxic. In this study, increasing toxicity appeared similarly to depend on the quantity of wet heat input as illustrated by the range of increasing temperatures. The relatively lower temperatures of scalding versus flame burns can accomplish similar dangerous effects; it is simply a quantitative matter of heat input.

Dermal cellular inflammation in burns. an insight into the function of dermal microvascular anatomy

The damage caused by thermal trauma is augmented by the subsequent inflammatory response in a similar fashion to reperfusion injury. Animal studies have demonstrated a significant role for neutrophils in this delayed damage, but little is known about the numbers of neutrophils or other leucocytes that enter human skin following burns. We have longitudinally examined profiles of leucocyte migration into five cases of human partial thickness burns in relation to continued dermal microvascular destruction during the acute post-burn period. All burn wounds had a rapid influx of neutrophils that was followed by a delayed influx of macrophages. Compared to the controls, the two superficial burns also had rapid and sustained influx of CD4 and CD8 lymphocytes via patent post capillary venules in the dermal superficial vascular plexus, whilst in the three deeper burns, in which this superficial vascular plexus was occluded, the number of lymphocytes decreased. These results suggest that the patterns of leucocyte extravasation were dependent on the initial level of vascular occlusion, indicating that the dermal microvascular anatomy plays a pivotal role in determining the composition of the extravascular inflammatory cell infiltrates. The potential importance of this finding is highlighted by the differences in wound behaviour associated with the different leucocyte profiles.

An open study comparing topical silver sulfadiazine and topical silver sulfadiazine-cerium nitrate in the treatment of moderate and severe burns

Sixty patients with moderate and severe burns were randomly assigned to receive topical silver sulfadiazine (SSD) alone (n=30) or SSD combined with cerium nitrate (SSD-CN) (n=30). There were four deaths in the SSD group and one in the SSD-CN group; more patients with higher risk severity survived in the SSD-CN group. Wound infection did not differ significantly between the groups. The rate of re-epithelialization of partial thickness burns was faster by 8 days in the SSD-CN group. The relatively dry shell-like eschar of the SSD-CN-treated burn allowed planned excisions with immediate autologous grafting and the tissue beneath was ready to accept grafting 11 days earlier than in the SSD group (p=0.03). This resulted in a significantly shorter hospital stay for those in the SSD-CN group than in the SSD group (23.3 vs. 30.7 days; p=0.03) with consequent cost savings. A higher incidence of transient stinging pain was reported with application of SSD-CN, but this was effectively managed with analgesics where necessary. The results of this study confirm the greater efficacy of SSD-CN in the treatment of burns patients.

The cytokine response to physical activity and training

Cytokines are soluble glycoproteins that are produced by and mediate communication between and within immune and nonimmune cells, organs and organ systems throughout the body. Pro- and anti-inflammatory mediators constitute the inflammatory cytokines, which are modulated by various stimuli, including physical activity, trauma and infection. Physical activity affects local and systemic cytokine production at different levels, often exhibiting striking similarity to the cytokine response to trauma and infection. The present review examines the cytokine response to short term exercise stress, with an emphasis on the balance between pro- and anti-inflammatory mechanisms and modulation of both innate and specific immune parameters through cytokine regulation. The effects of long term exercise on cytokine responses and the possible impact on various facets of the immune system are also discussed, with reference to both cross-sectional and longitudinal studies of exercise training. Finally, the validity of using exercise as a model for trauma and sepsis is scruti- nised in the light of physiological changes, symptomatology and outcome, and limitations of the model are addressed. Further studies, examining the effect of exercise, trauma and infection on novel cytokines and cytokine systems are needed to elucidate the significance of cytokine regulation by physical activity and, more importantly, to clarify the health implications of short and long term physical activity with respect to overall immune function and resistance to infection.

Increased activity of lymph node cells in experimental thermal injury: changes in accessory cells in injured area-draining lymph nodes

Accessory cell content and some of their functional characteristics were determined in regional lymph nodes which drain burn injury (DLN) in rats. Increase in percentages of non-specific esterase-positive cells and NBT+ macrophages and in numbers of dendritic cells were noted in cytospin preparations of draining lymph node cells (DLC) 24 and 72 h following thermal injury. An accumulation of B cells was also noted in the DLN paracortex region at these time points. Enrichment of ED1+ (rat macrophage marker) cells was noted in the adherent DLC population. Increased activity of interleukin-1 (IL-1) in conditioned medium from adherent DLC population and the increased stimulatory capacity of whole DLC or dendritic cell enriched-DLC fraction were noted in functional assays. Enrichment in accessory cells and an increase in their functional activity could contribute to the endogenous activity of regional lymph nodes which drain burned areas.

Comparison of lymphocyte populations in cutaneous and electrical burn patients: a clinical study

Immunosuppression following thermal injury has been noted in recent years. Both cellular and humoral immune systems have been reported to be affected. The present study aimed to compare the quantitative differences between cutaneous and electrical burn patients in respect to the partition and levels of lymphocyte populations. From March 1997 through February 1998, 15 patients with major thermal injury or high voltage electrical injury were included in this clinical prospective study. Blood samples were collected at three and seven days postburn. The evaluation of lymphocyte populations of patients was performed by SimulTest IMK plus. T cell and B cell populations, activated T cells, natural killer and helper T cell levels were all suppressed in both groups. Suppressor T cell levels were elevated in electrical burn group at both three and seven days. Therefore, CD 4/CD 8 ratios were more suppressed in electrical burn group. In conclusion, lymphocyte populations in electrical burn patients and also contributing factors which play important roles in the development of sepsis in both group need to be investigated further.

Role of nitric oxide in depressed lymphoproliferative responses and altered cytokine production following thermal injury in rats

Immunodeficiency follows extensive burns. We investigated some underlying mechanisms in rats, 10 days after a full-thickness skin burn affecting 20% of total body surface area. In both normal and burned rats the splenocyte proliferative response to Con A was linearly and negatively correlated with nitric oxide (NO) production. In all burned rats, the proliferative response was depressed by more than 80% and NO production corresponded to a nitrite concentration above 20 microM. Proliferative responses in burned rats were fully restored in the presence of 250 microM NG-monomethyl-L-arginine (NMMA). A time course study of NO production in response to Con A, LPS, anti-CD3, and IFN-gamma showed that splenic macrophages from burned rats responded to direct and indirect stimuli more rapidly and more intensively than normal macrophages. In the second part of this work, the effect of the overproduction of NO on the synthesis of immunoregulatory and proinflammatory cytokines was investigated. Although it was inhibited, IFN-gamma production by splenocytes from burned rats remained sufficient for NO synthase induction and was restored by NMMA. Concomitantly, IL-2 concentration was enhanced but returned to normal in the presence of NMMA. TNF production was halved after burn injury and NMMA partially restored it. In contrast, IL-6 production was enhanced and increased further in the presence of NMMA. Therefore, cytokines were differently affected by burn injury and variously regulated by NO.

Pathophysiology of the burn wound and pharmacological treatment. The Rudi Hermans Lecture, 1995

The body's reaction to thermal injury is much more than an initial, local inflammatory response. The burn wound is a continuous, severe threat against the rest of the body due to invasion of infectious agents, antigen challenge and repeated additional trauma caused by wound cleaning and excision. The inflammatory mediators which control blood supply and microvascular permeability in the wound have been extensively studied and are largely understood. Attempts to suppress the inflammatory reaction by different drugs, have, however, been less successful. Extensive thermal injury and sepsis also results in immunosuppression. The defects causing immunosuppression are still very much under consideration. An understanding of these defects is essential for the development of therapies. The increasing interest in the control of the inflammatory reactions by cytokines may, in the near future, be of great importance.

T lymphocytes and immunosuppression in the burned patient: a review

Extensive thermal trauma results in impaired immune function which has been attributed to a reduction in T lymphocyte numbers, increased suppressor cell activity, serum suppressive factors and altered cytokine synthesis and receptor expression on T cells. Numeric and phenotypic changes in T lymphocytes, T cell proliferation and functional responses of T lymphocytes in recent studies using murine models and patients are described.

Post-traumatic activation of draining lymph node cells. II. Proliferative and phenotypic characteristics

Proliferative and phenotypic characteristics of cells in regional lymph nodes that drain burn injury were examined in rats on day 3 postburn, i.e. at the time of maximal spontaneous proliferation and of interleukin-2 and accessory cytokine (IL-1 and IL-6) production. The importance of IL-1 in spontaneous proliferation of draining lymph node cells was demonstrated by stimulation of IL-2-driven proliferation by recombinant IL-1 in vitro and by susceptibility of unstimulated proliferation to anti-IL-1 antibodies, while requirements for IL-6 in draining lymph node cell proliferation were less pronounced. Cell surface phenotyping revealed a slightly increased percentage of CD25+ cells in the blast cell population of freshly isolated draining lymph node cells after injury, which increased further during cultivation. Enrichment in CD8+ cells on day 3 following burn injury was demonstrated, while no changes in total cell population and CD4+ cells was noted. This was however preceded by pronounced percentual decrease of total T cells and CD4+ cells and by increases of B cells and MHC class II+ cells on day 1 postburn. Inhibition of draining lymph node cell proliferation by anti-MHC class II antibodies suggested that this proliferation was class II MHC dependent. The contribution of cell proliferation and/or cell influx to day 3 postburn draining lymph node cell activity is discussed.

Effect of constituents of burned skin and in vivo skin burning on the respiratory activity of rat liver mitochondria

The formation of toxic substances in the skin, due to the influence of thermal energy, is supposed to be one possible mechanism responsible for the high mortality rate after severe burns covering large areas of the body surface. The effects of low-molecular-weight volatile substances (dry distillates) generated after burning mouse skin were investigated. They led to reductions of the respiratory activity of rat liver mitochondria. Among other substances carbon disulphide, methylethylketone and pyrrole were isolated and characterized using gas chromatography. All of them had strong uncoupling effects on mitochondrial respiration. In a second study respiratory measurements were made on mitochondria from rats with 20-30 per cent TBSA full skin thickness burns. A decreased respiratory control ratio and thus uncoupling of mitochondrial respiration was found on days 1, 2 and 5 postburn. The basal mitochondrial respiration was significantly decreased on day 5, which could be important for the mortality mentioned above. Finally after cross-transplantations rats having burned skin grafted showed a reduction of the RCR when compared with rats with the unburned graft. Thus it can be concluded that toxic substances must have been present in burned skin.

Immunosuppression follows systemic T lymphocyte activation in the burn patient

A general consensus that thermal injury affects T lymphocyte function adversely is supported particularly by the observation that burned patients' lymphocytes secrete reduced levels of biologically active IL-2 in vitro. In the same patients, however, high serum concentrations of the low-affinity IL-2 receptor (IL2R alpha), a product of an IL-2-activated gene, have been observed. In this study a significant proportion of patients also demonstrated over-physiological levels (from 2 to 500 U/ml) of serum IL-2 ascertained by immunoassay. Increases in serum IL-2 content correlated significantly (P less than 0.02) with those of serum IL-2R alpha during the first week post-burn. Later, serum IL-2R alpha levels continued to increase up to 30 days while IL-2 eventually declined. Thus, augmented secretion of IL-2R alpha appears related to the high serum IL-2 content. Therefore refractoriness to further immune stimulation may be due to early activation of the lymphoid system, rather than to an intrinsic incapacity of T lymphocytes for generating sequential responses.

Soluble interleukin 2-receptor alpha secretion is related to altered interleukin 2 production in thermally injured patients

This study examines the relationship between the capacity for interleukin-2 (IL2) production and the magnitude of the in vitro and in vivo secretion of IL2R alpha in 43 patients with major burns (30-90 per cent total body surface area). Throughout the postburn period a significant (P less than 0.001-0.05) proportion of patients studied demonstrated increasingly high levels of serum IL2 ranging from 2 to over 500 U/mL. Serum IL2R alpha also increased, reaching its highest levels at 15-40 days postburn, while serum IL2 gradually declined. In this period in vitro IL2 production and IL2R alpha secretion in patient's cultures were significantly reduced compared to control. However, in parallel cultures supplemented with exogenous IL2, IL2R alpha levels could be significantly increased (2.5 fold). IL2R alpha levels also approached normal in peripheral blood mononuclear cell cultures from recovering patients whose in vitro IL2 production had improved. These observations suggest that in the burn patient altered synthesis and/or secretion of the soluble form of IL2R alpha may be related to IL2 content. Above physiological levels of IL2R alpha and its ligand in postburn serum also indicate that thermal injury induces strong in vivo activation of the lymphoid system.

Influence of burn-induced lipid-protein complex on IL1 secretion by PBMC in vitro

The lipid-protein complex (LPC) formed by thermal injury to skin, which has been shown to have a toxic effect on mice, and which suppresses the immune response, was tested for its specific influence on monocytes. Growth of bacterial endotoxin-stimulated peripheral blood mononuclear cells (PBMC) was inhibited in the presence of LPC, however, the inhibition was less at the time of the optimal rate of cell proliferation. Inhibition was proportional to LPC concentration. ConA-stimulated PBMC were also inhibited by LPC in a dose-related manner. PBMC, in the presence of LPC, secreted interleukin 1 (IL1) at an increasing rate as LPC concentration rose from 5 to 40 micrograms/ml, and the levels of IL1 which could be induced by endotoxin were increasingly amplified in the presence of LPC. In comparison to LPC, the native tissue proteins which were isolated from unburned skin by the same techniques which produced LPC from burned skin, were tested for their effect on PBMC. Native proteins had no effect on IL1 secretion, whether on background or endotoxin-stimulated levels. Thus, the thermally induced change in skin proteins has a specific effect on monocyte IL1 secretion which is not matched by the native proteins, indicating that burn injury to skin specifically affects the lymphokine cascade and consequent immune function.