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

Low-Density Granulocyte Contamination From Peripheral Blood Mononuclear Cells of Patients With Sepsis and How to Remove It - A Technical Report

Elucidating the mechanisms contributing to the dysregulated host response to infection as part of the syndrome is a current challenge in sepsis research. Peripheral blood mononuclear cells are widely used in immunological studies. Density gradient centrifugation, a common method, is of limited use for blood drawn from patients with sepsis. A significant number of low-density granulocytes co-purify contributing to low purity of isolated peripheral blood mononuclear cells. Whole blood anticoagulated with lithium heparin was drawn from patients with sepsis (n=14) and healthy volunteers (n=11). Immediately after drawing, the plasma fraction was removed and PBMC were isolated from the cellular fraction by density gradient centrifugation. Samples derived from patients with sepsis were subsequently incubated with cluster of differentiation 15 MicroBeads and granulocytes were depleted using magnetic-activated cell sorting. Core cellular functions as antigen presentation and cytokine secretion were analyzed in cells isolated from healthy volunteers (n=3) before and after depletion to confirm consistent functionality. We report here that depleting CD15⁺ cells after density gradient centrifugation is a feasible way to get rid of the low-density granulocyte contamination. Afterwards, the purity of isolated, functionally intact peripheral blood mononuclear cells is comparable to healthy volunteers. Information on the isolation purity and identification of the containing cell types are necessary for good comparability between different studies. Depletion of CD15⁺ cells after density gradient centrifugation is an easy but highly efficient way to gain a higher quality and more reliability in studies using peripheral blood mononuclear cells from septic patients without affecting the functionality of the cells.

Ficoll-separated mononuclear cells from sepsis patients are contaminated with granulocytes

OBJECTIVE

To determine the cell content and purity of Ficoll-separated peripheral blood mononuclear cells and granulocyte isolates in sepsis patients compared to healthy controls.

DESIGN AND SETTING

Prospective study in the adult and pediatric intensive care departments of the Erasmus University Medical Center in the Netherlands.

PATIENTS

Three sepsis patients (two adults, one child) and four healthy controls.

MEASUREMENTS AND RESULTS

Blood leukocytes were separated by Ficoll into an interface and a bottom fraction. The cell content and purity was analyzed by cytospin and flow-cytometric immunofluorescence. In sepsis patients, the interface consisted of 11-52% mononuclear cells only, due to high contamination with granulocytes (48-89%). This was in contrast to a high proportion of mononuclear cells (88-100%) in healthy controls. The bottom fraction showed a cell purity of >or=92% polymorphonuclear granulocytes in sepsis patients as well as in healthy controls.

CONCLUSIONS

Ficoll-separated leukocytes of sepsis patients are not suitable for studying mononuclear cells but can be used for studying granulocytes with high purity. The mononuclear cell fraction is highly contaminated with granulocytes. Additional separation techniques are necessary to obtain a pure cell fraction.

Immunosuppression follows systemic T lymphocyte activation in the burn patient

A general consensus that thermal injury affects T lymphocyte function adversely is supported particularly by the observation that burned patients' lymphocytes secrete reduced levels of biologically active IL-2 in vitro. In the same patients, however, high serum concentrations of the low-affinity IL-2 receptor (IL2R alpha), a product of an IL-2-activated gene, have been observed. In this study a significant proportion of patients also demonstrated over-physiological levels (from 2 to 500 U/ml) of serum IL-2 ascertained by immunoassay. Increases in serum IL-2 content correlated significantly (P less than 0.02) with those of serum IL-2R alpha during the first week post-burn. Later, serum IL-2R alpha levels continued to increase up to 30 days while IL-2 eventually declined. Thus, augmented secretion of IL-2R alpha appears related to the high serum IL-2 content. Therefore refractoriness to further immune stimulation may be due to early activation of the lymphoid system, rather than to an intrinsic incapacity of T lymphocytes for generating sequential responses.

Soluble interleukin 2-receptor alpha secretion is related to altered interleukin 2 production in thermally injured patients

This study examines the relationship between the capacity for interleukin-2 (IL2) production and the magnitude of the in vitro and in vivo secretion of IL2R alpha in 43 patients with major burns (30-90 per cent total body surface area). Throughout the postburn period a significant (P less than 0.001-0.05) proportion of patients studied demonstrated increasingly high levels of serum IL2 ranging from 2 to over 500 U/mL. Serum IL2R alpha also increased, reaching its highest levels at 15-40 days postburn, while serum IL2 gradually declined. In this period in vitro IL2 production and IL2R alpha secretion in patient's cultures were significantly reduced compared to control. However, in parallel cultures supplemented with exogenous IL2, IL2R alpha levels could be significantly increased (2.5 fold). IL2R alpha levels also approached normal in peripheral blood mononuclear cell cultures from recovering patients whose in vitro IL2 production had improved. These observations suggest that in the burn patient altered synthesis and/or secretion of the soluble form of IL2R alpha may be related to IL2 content. Above physiological levels of IL2R alpha and its ligand in postburn serum also indicate that thermal injury induces strong in vivo activation of the lymphoid system.