Intracellular and extracellular cytokine production by human mixed mononuclear cells in response to group B streptococci

Group B streptococci (GBS) are a major cause of severe infection in newborn s, pregnant females, and other immunocompromised hosts. Infection often inc ludes septicemia, shock, pneumonia, and respiratory failure. In previous st udies, we have reported that GBS induce marked production of tumor necrosis factor alpha (TNF-alpha) by human mononuclear cells. The present study was designed to measure the production of TNF-alpha as well as additional cyto kines, including interleukin 1 beta (IL-1 beta), IL-6, IL-8, IL-12, and gam ma interferon (IFN-gamma) but also to determine from what cells and at what time point during incubation with GBS that these cytokines are produced, M ixed mononuclear cells were incubated with heat-killed GBS, media alone, or 1 mu g of Escherichia coli lipopolysaccharide (LPS), Brefeldin A was added to each sample prior to staining, which prevented the export of cytokines by the Golgi apparatus. The cells were then stained with the appropriate co njugated antibodies and analyzed by using a flow cytometer. Results indicat e that intracellular cytokines appear, in almost all cases, simultaneous to or before secreted proteins are detected. In contrast to the response to L PS, where TNF-alpha, IL-1 beta, IL-6, and IL-8 appear almost simultaneously , the human monocyte response to GBS results in the production of TNF-alpha but delayed appearance of IL-1 beta, IL-6, and IL-8. The lymphocyte respon se to GES was also strikingly different from that to LPS in that both secre ted IFN-gamma and IL-12 was detected, while LPS failed to induce production of these critical cytokines. This suggests an important role for TNF-alpha , IFN-gamma, and IL-12 in GBS pathogenesis and/or immunity.