Ficoll-Hypaque leukocyte preparations from burned patients contain activated nonlymphoid cell populations that take up thymidine.

Previously, we reported that Ficoll-Hypaque-purified leukocytes from burned patients were activated in vivo, even when the mitogen response of these cells was depressed. In these patients, the SBT (endogenous blastogenesis), but not the mitogen response predicted sepsis. The current experiments were performed to clarify why the SBT is increased even when mitogen-stimulated blastogenesis is impaired. We found that neither selective lymphocyte subpopulation (OKT3, T4, T8), nor macrophage depletion returned the increased SBT to normal and that by phenotype and flow cytometric morphology, the Ficoll-Hypaque-purified leukocyte preparations of the burned patients contained fewer lymphocytes than controls (p less than 0.001). Discontinuous Percoll gradients and sheep-RBC rosetting were used to determine the relative contribution of T cells and non-T cells to the increased SBT. These studies indicated that both T cells and non-T cells were activated; however, the non-T cells were primarily responsible for the increased SBT. Thus the peripheral blood of burned patients contains a large fraction of metabolically active non-mononuclear cells that cosediment with mature lymphocytes and could result in artifactual alterations in the assessment of lymphocyte function by in vitro tests.