Monocytes Are the Major Producers of Interleukin-1β in an Ex Vivo Model of Local Cytokine Production

Interleukin-1 beta (IL-1 beta) is an early proinflammatory cytokine with multiple effects. Several cells are capable of synthesizing this cytokine, but little is understood about which cell produces IL-1 in disease states. We examined the cellular source of IL-1 in lipopolysaccharide (LPS)-stimulated human whole blood. Cytospin preparations of leukocytes were stained for IL-1 beta using a murine monoclonal antibody and staining intensity evaluated. In multiple time course experiments, LPS-stimulated whole blood showed increases in both plasma and cell-associated IL-1 beta over 8 h as measured by ELISA (at 4 h, plasma IL-1 beta, 7.2 +/- 2.7 ng/ml; cell lysates, 1.3 +/- 0.2 ng/ml). Northern blot confirmed the upregulation of IL-1 beta mRNA in leukocytes. Immunohistochemistry showed low-level PMN positivity with no increase in staining intensity over time. In contrast, monocytes displayed a marked increase in staining intensity by 4 h, correlating with increases in cell-associated and plasma IL-1 levels. Lymphocytes remained negative throughout. Our data demonstrate that monocytes represent the major source of IL-1 beta in a human ex vivo model that simulates physiologic conditions and stimuli.