The presence of aberrant activation of suppressor T lymphocytes and inhibitory monocytes (ø) was examined in the Ficoll-Hypaque-purified mononuclear cells from 18 thermally injured and 20 splenectomy patients. The cells were either depleted of T cells by the E-rosette method in the burn patients or of ø by filtration over Sephadex G-10 columns in the splenectomy patients. Undepleted and depleted cells were then examined for their phytohemagglutinin (PHA) response and ability to suppress the "one-way" mixed leukocyte response (MLR) of normal individuals. Undepleted cells from burn patients had depressed PHA responses and gained suppressive activity by 5 to 8 days after injury, suppressing the normal MLR an average of 57.5% compared with only 14.0% suppression by T-depleted cells (P < 0.01). The PHA response of splenectomy patients' cells was markedly depressed to 22% of normal at 12 to 16 days after operation, compared to a supranormal (mean 113%) response after removal of ø by filtration (P < 0.01). These data demonstrate the activation of suppressor T cells after thermal injury and an increase in inhibitory monocytes after splenectomy. Such regulatory cells may have a major role in decreasing the immunocompetence of these patients.
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