Immature T lymphocytes after injury characterized by morphology and phenotypic markers

Immune response in burn patients in relation to HIV infection and sepsis

The post-burn immune dysfunction predisposes patients to sepsis and multiple organ failure leading to increased mortality. HIV infection also results in a depressed immune response. The combination of burn injury and HIV might therefore lead to an increased morbidity and mortality as compared to non-HIV infected burn patients. Twenty burn patients and 10 healthy volunteers were included in a prospective study. To evaluate their immune status, CD4+ and CD8+ T-lymphocyte counts were determined in peripheral blood. HIV serology samples were obtained on admission. Bacteriological cultures were obtained from wound surface samples and wound tissue biopsies. Six burn patients were HIV infected. Clinical signs of sepsis were observed in 10 patients. The number of CD4+ T-lymphocytes were lower in burn patients compared to healthy volunteers (P < 0.05). HIV infected burn patients had lower CD4+ lymphocyte counts than non-HIV infected patients (P < 0.05). Patients with clinical signs of sepsis had lower CD4+ counts compared to patients without sepsis (P < 0.05). There was no difference in the mortality rate or the length of hospitalisation between patient groups. Burn injury, HIV infection and sepsis independently result in immunosuppression.

Serum levels of different forms of soluble CD38 antigen in burned patients

The level of the total and dimeric (oligomeric) forms of soluble CD38 antigen (sCD38) has been determined by an ELISA sandwich method in serum from burned patients (n=18) and healthy volunteers (n = 25). The serum level of total sCD38 was insignificantly increased in patients at the stage of burn shock (135 +/- 10.8 U/ml, mean +/- S.E.M.) and significantly decreased between 4 and 14 postburn days in comparison with volunteers (69.5 +/- 10.8 U/ml versus 121 +/- 7.8 U/ml, P < 0.05). The serum level of soluble dimeric CD38 in burned patients was statistically lower than normal during all periods of observation (45.3 +/- 8.8 and 130 +/- 6.2 U/ml, respectively, P < 0.01). The relative number of CD38(+) lymphocytes was increased during the period of shock in comparison with healthy volunteers (21 +/- 1.6% versus 13 +/- 1.1%, P < 0.05). There were no correlations between number CD38(+) lymphocytes and total sCD38 or dimeric sCD38 serum levels. These data suggest that the mCD38 expression and serum level of total sCD38 are a markers the early postburn lymphocytes activation. The decrease of dimeric sCD38 level can reflect its dissociation to monomeric form in burned patients.

Lymphocyte function in wound healing and following injury

BACKGROUND

Injury activates a cascade of local and systemic immune responses.

METHODS

A literature review was undertaken of lymphocyte function in wound healing and following injury.

RESULTS

Lymphocytes are not required for the initiation of wound healing, but an intact cellular immune response is essential for a normal outcome of tissue repair. Injury affects lymphocyte immune mechanisms leading to generalized immunosuppression which, in turn, increases host susceptibility to infection and sepsis. Although the exact origin of post-traumatic immunosuppression remains unknown, stress hormones and immunosuppressive factors, such as inflammatory cytokines, prostaglandin E2 and nitric oxide, affect lymphocyte function adversely. Post-traumatic impairment of T lymphocyte immune function is reflected in decreased lymphocyte numbers, as well as altered T cell phenotype and activity. Antibody-producing B lymphocytes are variably affected by injury, probably secondary to alterations of T lymphocyte function, as a result of their close interaction with helper T cells. Therapeutic modulation of the host immune response may include non-specific and specific interventions to improve overall defence mechanisms.

CONCLUSION

Early resuscitation to restore lymphocyte function after injury is important for tissue repair and the prevention of immunosuppression.

Immune deficiency following thermal trauma is associated with apoptotic cell death

Thermal injury-associated specific immune deficiency occurs despite indicators of systemic activation of the lymphoid compartment. We investigated the possibility that postburn immune failure and T cell activation are casually related through activation-induced (apoptotic) cell death. The relationship between the cellular immune response and cell mortality was examined in cultures of peripheral blood mononuclear cells (PBMC) from 14 immunosuppressed patients with extensive burns (35-90% total body surface area). Impaired cellular immunity coincided with significantly reduced cell viability as ascertained by propidium iodide staining and dye reduction assays. Following stimulation with the mitogenic lectin, phytohemagglutinin (PHA), the majority of DNA in patient cultures was fragmented, suggesting the occurrence of apoptotic cell death. Even without stimulation a portion of patient cells was apoptotic as indicated by oligonucleosomal bands on agarose gel electrophoresis. Exogenous interleukin-2 or phorbol ester markedly reduced constitutive as well as PHA-induced DNA fragmentation. In situ demonstration of DNA strand breaks in freshly isolated patient PBMC, by a TdT-based labeling technique, confirmed that a larger fraction (up to 60%) of circulating lymphocytes was undergoing apoptosis on the periphery. These novel observations suggest that apoptosis may play a major role in thermal injury-related cellular immunodeficiency.

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.

Different lymphocyte compartments respond differently to mitogenic stimulation after thermal injury

Because of the association between the development of an immunocompromised state and an increased risk of infection, increasing attention has been focused on describing and characterizing the immune consequences of thermal injury. Results of human studies are largely based on the in vitro responsiveness of peripheral blood leukocytes, while splenocytes are generally used in the animal studies. Because the response of lymphocytes from different lymphocyte compartments may vary, we compared the responses of murine peripheral blood, splenic, Peyer's patch, and mesenteric lymph node lymphocytes to a battery of mitogens after thermal injury. Burn-induced immunosuppression was maximal in the splenic lymphocyte compartment, where the responses to all three test mitogens were depressed throughout the 28-day postburn study period. Although the PHA-induced mitogen response of lymphocytes from the other three lymphoid compartments remained suppressed throughout the study period, the response to the mitogens Con-A and PWM generally returned to normal or supranormal levels by the seventh postburn day, Therefore it appears that the effect of a thermal injury on lymphocyte function varies according to the lymphocyte compartment examined and the mitogen tested. These results raise the question of whether animal studies using splenic lymphocytes can be correlated with human studies performed on circulating blood lymphocytes.

In vitro cell-mediated immunity after thermal injury is not impaired. Density gradient purification of mononuclear cells is associated with spurious (artifactual) immunosuppression

Mononuclear cells isolated by density gradient centrifugation from the peripheral blood of burn patients, but not healthy volunteers, are contaminated with large numbers of nonmononuclear cells. These contaminating leukocytes could cause artifactual alterations in standard in vitro tests of lymphocyte function. Thus, we compared the in vitro blastogenic response of density gradient purified leukocytes and T-cell purified lymphocytes from 13 burn patients to mitogenic (PHA) and antigenic stimuli. The mitogenic and antigenic response of the patients' density gradient purified leukocytes were impaired compared to healthy volunteers (p less than 0.01). However, when the contaminating nonlymphocytes were removed, the patients' cells responded normally to both stimuli. Thus, density gradient purified mononuclear cells from burn patients are contaminated by leukocytes that are not phenotypically or functionally lymphocytes. Since the lymphocytes from burn patients respond normally to PHA and alloantigens after the contaminating nonlymphocyte cell population has been removed, it appears that in vitro assays of lymphocyte function using density gradient purified leukocytes may give spurious results.