Whole-blood assays for cytokine production.

Substantial interest has been generated by the potential roles of the cytokines in health and disease (1). This has prompted considerable investigation into how these mediators are regulated to answer such basic questions as which stimuli initiate transcription and what factors are responsible for inhibiting secretion. This has resulted in elegant studies that have begun to define the intracellular-signaling pathways responsible for the upregulation of cytokines (2,3). Many of these studies have been done with cultures of cell lines derived from cancers or primary cultures of isolated fibroblasts, endothelial cells, or isolated mononuclear cells. Whereas these studies have provided substantial insight, they may be limited in their scope because they do not include all cell-cell or cell-protein interactions that take place in vivo. Other studies have used endotoxin injection into normal human volunteers to study the upregulation of cytokines (4,5). These studies with the normal volunteers provide precise information about the kinetics of cytokine production, but they are difficult to perform and very expensive. The whole-blood model serves as a useful bridge between using normal volunteers and isolated peripheral blood mononuclear cells. For critically ill patients it would be impossible to perform endotoxin infusion studies, and it would even be difficult to conduct these types of studies in chronically ill patients. Whole blood may also be used to study the immune responses of such patients in an attempt to determine how their cytokine regulation differs from normal individuals.