Severely depressed interleukin-17 production by human neonatal mononuclear cells.

BACKGROUND: The role of T-helper 17 cells (Th17) in neonatal host defense remains to be fully elucidated. Interleukin (IL)-17 plays an important role in the immune response to bacterial and fungal pathogens by promoting inflammation. METHODS: We examined neonatal production of IL-17 in mixed mononuclear cells (MMCs) isolated from umbilical cord blood for comparison with adult peripheral blood mononuclear cell controls. RESULTS: IL-17 production was profoundly diminished in MMCs isolated from cord blood when compared with MMCs from adult blood. This was associated with a marked reduction in the population of CCR6+ IL-17(+) T-cells in the neonatal cord blood. We also found diminished intracellular formation of IL-17, and diminished IL-17 responses to both group B streptococci (GBS) and Escherichia coli. Neonatal mononuclear cells were found to adequately phosphorylate signal transducer and activator of transcription 3, pY705, and pS727. We and others have reported markedly reduced interferon-γ production by neonate mononuclear cells exposed to GBS. Here, we correct that profound abnormality with added IL-17. CONCLUSION: Our results suggest that profound deficiency of IL-17 production associated with a marked decrease in Th17 cells likely contributes significantly to the increased susceptibility of human neonates to invasive bacterial and fungal infections.

Multiplex analysis of toll-like receptor-stimulated neonatal cytokine response.

BACKGROUND: The human neonate's increased susceptibility to bacterial infections is not completely understood. Toll-like receptors (TLRs) have been recognized as pattern-recognition receptors critical to the innate immune response. TLR function in neonates, however, remains incompletely defined. OBJECTIVE: To examine regulatory and proinflammatory cytokine responses to TLR-1-6 stimulation of cord blood compared to adult blood. METHODS: We stimulated cord blood with ligands for each of TLRs 1-6 and compared these responses to adult controls. The following TLR ligands were utilized: Pam3CSK4 (TLR-1 and 2), zymosan (TLR-2 and 6), poly I:C (TLR-3), LPS (TLR-4), and flagellin (TLR-5). Cytokine production was measured with an assay developed in-house utilizing multi-analyte technology. RESULTS: TLR-1-6 stimulation produced higher concentrations of proinflammatory cytokines (IL-1beta, IL-6, and IL-8) in cord blood compared to adult blood, with the exception of TLR-4-stimulated TNF-alpha production, which was significantly lower in cord blood (319 pg/ml) compared to adult blood (645 pg/ml; p = 0.027). In contrast, TLR-1-6 stimulation resulted in decreased concentrations of Th1 and Th2 cytokines in cord blood compared to adult blood, with significantly diminished production of IL-12 (TLRs 1/2, 2/6, 3 and 4), IL-13 (TLR-1-6), and IL-10 (TLR-4). CONCLUSION: Cord blood production of regulatory Th1 and Th2 cytokines following TLR stimulation is decreased compared to that of adult blood. In contrast, TLR-stimulated proinflammatory cytokine production was markedly higher in neonates than in adults, with the exception of TLR-4-induced TNF-alpha production. The human neonate's increased susceptibility to bacterial infections may be related to abnormal TLR responsiveness, with enhanced proinflammatory and decreased regulatory cytokine production.

Defective production of IL-18 and IL-12 by cord blood mononuclear cells influences the T helper-1 interferon gamma response to group B Streptococci.

Human neonates are uniquely susceptible to group B streptococcal (GBS) infections. We have shown that neonatal mixed mononuclear cells have a deficiency in the production of the T helper-1 (Th-1) cytokine, interferon gamma (IFN-gamma), and that incubation of neonatal neutrophils with recombinant IFN-gamma corrects these neutrophil defects. IL-12 and the more recently described IL-18 are also Th-1 type cytokines that are able to induce the production of IFN-gamma in the presence of bacteria and bacterial products. We examine the ability of GBS to induce the production of IFN-gamma, IL-18, and IL-12 by cord blood mixed mononuclear cells and compared these results with the IFN-gamma, IL-18, and IL-12 response of mixed mononuclear cells from adult blood. We demonstrate that cord blood mixed mononuclear cells produced significantly less IFN-gamma, IL-18, and IL-12 in response to GBS compared with mixed mononuclear cells from adults. Cord blood mixed mononuclear cells' production of IFN-gamma is enhanced by added recombinant IL-18 and IL-12. The maximal cord blood cell production of IFN-gamma, in response to GBS, is achieved by priming the cells with both IL-18 and IL-12. We conclude that neonatal mixed mononuclear cells exhibit deficiencies in three main Th-1 type cytokine responses, IFN-gamma, IL-12, and IL-18. This combined Th-1 type cytokine deficiency may contribute to the enhanced susceptibility of the human neonate to GBS and other microbial infections.