Impairment of T cell activation in burn patients: A possible mechanism of thermal injury-induced immunosuppression

In the burn patient, the mechanisms leading to impaired T lymphocyte activity are unclear. The capacity for T cell proliferation and the expression of Tac antigen (IL-2 receptor) was assessed during the post-burn period in patients with injuries ranging from 5-68% total body surface area. T cell-dependent (polyclonal) immunoglobulin synthesis, mixed lymphocyte reaction and Interleukin-2 production were also determined in these patients and correlated with survival. Surviving patients demonstrated a transient reduction while terminal patients exhibited a permanent reduction in the number of Tac (+) lymphocytes, unrelated to the absolute number of T cells, during the post-burn period. The reduced percentage of IL-2 receptor-expressing T cells coincided with the suppressed antibody response and reduced alloreactivity. Although the concentration of IL-2 was decreased in all patients throughout the hospitalization period, surviving patients showed a gradual increase in its production while terminal patients gradually decreased to undetectable levels. Exogenous recombinant IL-2 induced a significant enhancement of in-vitro polyclonal immunoglobulin production and blastogenesis in the mixed lymphocyte reaction in immunosuppressed patients who demonstrated up to 50% reduction in the percentage of IL-2 receptor positive cells. Thus, the reduced capacity for production of and response to IL-2 after thermal injury may lead to the immunosuppression due to a lack of T lymphocyte clonal expansion. The permanent nature of this defect in patients who died from fatal sepsis may suggest a causative relationship.