J. Jeremy Wood

Inadequate interleukin 2 production. A fundamental immunological deficiency in patients with major burns.

We studied the production of the two major mediators of cellular immune responses, Interleukin 1 (IL-1) and Interleukin 2 (IL-2), by the peripheral blood mononuclear cells of 23 burn patients (16 men, seven women, mean age 48.9 years) compared with 23 matched controls (16 men, seven women, mean age 46.7 years). Serial measurements were made of IL-1 production by adherent mononuclear cells after stimulation with lipopolysaccharide and of IL-2 production by lymphocytes after stimulation with phytohemagglutinin (PHA). Eighty determinations of IL-2 production by lymphocytes from 12 patients with greater than 30% body surface area burn revealed a mean IL-2 production of 0.71 u as compared with a mean of 1.23 u for patients with less than 30% burns (p = 0.04). Patients with greater than 30% body surface area burns had significantly reduced IL-2 production (p ≤ 0.05) until 60 days after injury, whereas those with smaller burns had reduced IL-2 production only at 20–29 and 30–39 days postburn. Nine burn patients with systemic sepsis showed significantly lower IL-2 production (p = 0.03) at 10–29 days postburn than nonseptic patients, and significantly less IL-2 production during septic episodes. Eight patients with greater than 50% suppression of lymphocyte response to PHA produced less IL-2 (0.4 u) than patients with less than 50% suppression, (1.07 u, p = 0.004). IL-1 production was significantly elevated as compared with controls (4.45 u vs. 3.6 u, p = 0.05) early after injury, but was subsequently within the normal range regardless of burn size. The percentage of circulating helper T-lymphocytes, the principal source of IL-2, was also reduced, although this did not always correlate with IL-2 production, which remained depressed after recovery of the helper T-cell population. These results indicate that failure to produce IL-2, a powerful mediator of cellular immune responses, is an important mechanism underlying the defective cell mediated immunity seen in burn patients.

Depression of cellular immunity after multiple trauma in the absence of sepsis

We have previously reported that severe burn injury was regularly accompanied by impaired lymphocyte responses to T cell mitogens, circulating suppressor lymphocytes, and serum factors suppressive of lymphocyte activation. However, in burned patients it was difficult to determine whether these manifestations of suppressed immunity were predictive of, or the result of, sepsis which was ubiquitous in this population. In an attempt to clarify this issue, we have studied 31 patients with multiple trauma (without burns) mean age, 31 years; average injury severity score, 22; range, 9-56; in whom sepsis was less common. Patients were tested for lymphocyte response to the T cell mitogens PHA and Con A, the percentage of circulating putative suppressor (OKT8) and helper (OKT4) T cells using monoclonal antibodies, circulating suppressor cell activity as revealed by functional assays, and serum suppression of lymphocyte activation. Patients were compared with ten normal volunteers (mean age, 32) studied simultaneously. Significant suppression (greater than 50% compared with controls) in lymphocyte responses to mitogens 1 to 5 days after injury was seen in 12 patients, was accompanied by a shift in the ratio of helper (OKT4) to suppressor (OKT8) T cells (patients, 0.96:1; normals, 1.82:1; p less than 0.01), and was followed by the appearance of significant (greater than 50%) serum suppressive activity in six of the 12 patients. Circulating suppressor cell activity as revealed by functional assays was also seen early after injury in three of 12 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of natural killer-cell function in humans following thermal and traumatic injury.

Depressed cell-mediated and humoral immune functions have been reported to occur following severe thermal and traumatic injury. In this study we have questioned whether another immune function, natural killing (NK), is also disturbed in these injured patients. Twenty-two thermally injured patients with burns ranging from 5 to 75% of the total body surface area and 15 traumatically injured patients with injury severity scores ranging from 9 to 56 were followed postinjury and compared to 29 age-matched controls. NK activity was measured as the percentage cytotoxicity in chromium-51 release assays with K562 target cells. The more severely burned patients had significantly depressed NK activity for the 40-day period following injury that remained reduced for the duration of the study. Patients with lesser burns had reduced NK-cell function for the initial 10-day period postburn that returned slowly to the normal range. Traumatically injured patients had depressed NK-cell function during the 3- to 6-day period postinjury. The percentage of cells bearing phenotypic markers for the groups in which Nk cells are found was either normal or elevated in these patients. A correlation was found between NK activity and interleukin 2 generation by mononuclear cells from these patients. In order to investigate the mechanism of NK suppression in these patients, NK-cell function was studied following the infusion of cortisol, epinephrine, and glucagon into volunteer subjects in amounts known to reproduce serum levels seen following injury of moderate severity. NK-cell function was reduced an average of 66% following infusion, suggesting that the inhibition of NK-cell function seen in patients may be mediated by the stress response to injury.

Changes in T lymphocyte subsets following injury. Assessment by flow cytometry and relationship to sepsis.

The increased susceptibility of severely injured patients to infection and death from sepsis has been attributed to abnormalities in cell-mediated immunity. The authors therefore assessed the relative number of peripheral blood T helper cells and T suppressor/cytotoxic cells and total T lymphocytes identified by the monoclonal antibodies (McA) OKT4, OKT8, and OKT3, respectively, in 25 patients with burns from 5 to 85% total body surface area (TBSA) (mean: 40%) and 21 patients with nonthermal injuries (mean Injury Severity Score (ISS): 21.4). Patients were compared to 21 healthy controls. Cells reacting with the McA were detected by flow cytometry, which enabled the examination of a population of cells the size of T lymphocytes, excluding larger contaminating cells that might bind the McA. Patients with burns of 30% TBSA or greater had a significant reduction (p less than or equal to 0.05) in OKT3+ cells up to 50 days post-burn. Both septic and nonseptic burn patients had reduced numbers of OKT3+ cells, as did patients after nonthermal injury, suggesting that this reduction was due to the injury itself. Patients with smaller burns (less than 30% TBSA) as a group did not have reduced OKT4+ cells, whereas those with larger burns showed significant reductions in OKT4+ cells (P less than or equal to 0.05) at 0 to 5, 6 to 10, 11 to 20, 21 to 30, and 41 to 50 days post-burn. Seven burn patients who became septic 10 days post-burn or later had significantly lower OKT4+ cells within 10 days of injury (mean: 33.75% +/- 7.4 SEM) than 10 patients who remained free of sepsis (mean: 42.2% +/- 5.4, p = 0.004). Patients with uncomplicated nonthermal injuries failed to show any significant reduction in OKT4+ cells. Following thermal injury, a reduction in OKT8+ cells was observed up to 10 days in patients with burns less than 30% TBSA, and up to 20 days in patients with larger burns. In both groups, at no time were increased OKT8+ cells found to correlate with clinical events. In patients with nonthermal injury, OKT8+ cells generally remained near the normal range.

Immature T lymphocytes after injury characterized by morphology and phenotypic markers.

Changes in the peripheral blood mononuclear cell (PBMC) population in patients following both thermal and nonthermal injury were defined by both morphological characteristics and surface phenotype with the monoclonal antibodies T6, OKT9, OKT10, and OKIa1, using a fluorescence activated flow cytometer with gating to separate small cells of the lymphocyte series from larger forms. Lymphocytes with surface antigens that bind T6, OKT9, and OKT10 are rarely found in the peripheral blood of adult patients, except in those with malignancies of the lymphoid system. In both burn and trauma patients the percentage of lymphocytes in the PBMC population after Ficoll-Hypaque separation was significantly reduced as compared with normal controls due to increases in the number of granulocytes, large granular lymphocytes (LGL), and monocytes, often present in immature forms. T6 cells were found in significantly greater numbers in both burn and nonthermal injury patients than in a control group using both small and wide gate settings on the fluorescence-activated flow cytometer. Significant increases in the number of T9+ cells also were observed in both groups for a prolonged period following injury. Significantly increased numbers of the T10+ and Ia1+ cells were detected in burn patients. The response to injury, therefore, involves the appearance in the peripheral blood of immature cells that may express T6, T9, T10, and Ia1 surface antigens. These cells may be present in quantities otherwise seen only in malignant disease.