Intracellular and Extracellular Cytokine Production by Human Mixed Mononuclear Cells in Response to Group B Streptococci

Abstract

Group B streptococci (GBS) are a major cause of severe infection in newborns, pregnant females, and other immunocompromised hosts. Infection often includes septicemia, shock, pneumonia, and respiratory failure. In previous studies, we have reported that GBS induce marked production of tumor necrosis factor alpha (TNF-␣) by human mononuclear cells. The present study was designed to measure the production of TNF-␣ as well as additional cytokines, including interleukin 1␤ (IL-1␤), IL-6, IL-8, IL-12, and gamma interferon (IFN-␥) but also to determine from what cells and at what time point during incubation with GBS that these cytokines are produced. Mixed mononuclear cells were incubated with heat-killed GBS, media alone, or 1 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 conjugated antibodies and analyzed by using a flow cytometer. Results indicate that intracellular cytokines appear, in almost all cases, simultaneous to or before secreted proteins are detected. In contrast to the response to LPS, where TNF-␣, IL-1␤, IL-6, and IL-8 appear almost simultaneously, the human monocyte response to GBS results in the production of TNF-␣ but delayed appearance of IL-1␤, IL-6, and IL-8. The lymphocyte response to GBS was also strikingly different from that to LPS in that both secreted IFN-␥ and IL-12 was detected, while LPS failed to induce production of these critical cytokines. This suggests an important role for TNF-␣, IFN-␥, and IL-12 in GBS pathogenesis and/or immunity.

Expression of intracellular cytokines, HSP72, and apoptosis in monocyte subsets during exertional heat stress in trained and untrained individuals

“…NF-B p65 translocation occurs within minutes of extracellular stimulation, and subsequent intracellular protein accumulation follows within 30 -60 min (26). Typically, intracellular proteins appear before or simultaneously with extracellular protein (38). Thus the appearance of circulating TNF-␣ in our subjects (68) before intracellular accumulation (Fig.…”

Group B Streptococci Exposed to Rifampin or Clindamycin (versus Ampicillin or Cefotaxime) Stimulate Reduced Production of Inflammatory Mediators by Murine Macrophages

“…The increased incidence of invasive disease due to GBS in the newborn is due to frequent exposure to the organism (approximately 25% of women are colonized with GBS) in the context of specific deficiencies of neonatal host defense-particularly the diminished production and delivery of neutrophils to the site of infection and the frequent lack of specific antibody against the infecting serotype (5-7). Neonatal monocytes and macrophages are also impaired compared with macrophages from older children and adults, but are capable of producing large amounts of inflammatory mediators such as TNF in response to GBS (8,9). It is likely that excessive production of inflammatory mediators, including TNF and NO, contributes to the severity of sepsis and meningitis due to GBS, though the role of exuberant or unbalanced production of proinflammatory mediators in the pathogenesis of sepsis remains controversial (10).…”

Pneumococcal Infections in Humans Are Associated with Increased Apoptosis and Trafficking of Type 1 Cytokine-Producing T Cells

“…In accordance with this, it has been suggested that IFN-␥ produced by the NK or T cell is of importance in the host defense against S. pneumonia (23). In vitro experiments have shown that Streptococcus pyogenes strains induce production of IFN-␥ (type 1 response), but only weakly induce production of IL-4 (16,18). Furthermore, IFN-␥ rather than IL-4 is the dominant cytokine elicited in tonsils in vivo (1).…”