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Neonates are highly susceptible to disseminated infections, which are often fatal. Numerous distinctions have been described between neonatal and adult responses to infection, including blunted inflammatory cytokine production, skewed T-helper-cell [...], Newborn infants are highly susceptible to infection. This defect in host defence has generally been ascribed to the immaturity of neonatal immune cells; however, the degree of hyporesponsiveness is highly variable and depends on the stimulation conditions (1-7). These discordant responses illustrate the need for a more unified explanation for why immunity is compromised in neonates. Here we show that physiologically enriched [CD71.sup.+] erythroid cells in neonatal mice and human cord blood have distinctive immunosuppressive properties. The production of innate immune protective cytokines by adult cells is diminished after transfer to neonatal mice or after co-culture with neonatal splenocytes. Neonatal [CD71.sup.+] cells express the enzyme arginase-2, and arginase activity is essential for the immunosuppressive properties of these cells because molecular inhibition of this enzyme or supplementation with L-arginine overrides immunosuppression. In addition, the ablation of [CD71.sup.+] cells in neonatal mice, or the decline in number of these cells as postnatal development progresses parallels the loss of suppression, and restored resistance to the perinatal pathogens Listeria monocytogenes and Escherichia coli (8,9). However, [CD71.sup.+] cell-mediated susceptibility to infection is counterbalanced by [CD71.sup.+] cell-mediated protection against aberrant immune cell activation in the intestine, where colonization with commensal microorganisms occurs swiftly after parturition (10,11). Conversely, circumventing such colonization by using antimicrobials or gnotobiotic germ-free mice overrides these protective benefits. Thus, [CD71.sup.+] cells quench the excessive inflammation induced by abrupt colonization with commensal microorganisms after parturition. This finding challenges the idea that the susceptibility of neonates to infection reflects immune-cell-intrinsic defects and instead highlights AA processes that are developmentally more essential and inadvertently mitigate innate immune protection. We anticipate that these results will spark renewed investigation into the need for immunosuppression in neonates, as well as improved strategies for augmenting host defence in this vulnerable population.

Author(s): Vasiliki Anest [1, 2]; Julie L. Hanson [1, 2]; Patricia C. Cogswell [1]; Kris A. Steinbrecher [1]; Brian D. Strahl [1, 2, 3]; Albert S. Baldwin (corresponding author) [1, [...]

Newborn infants are highly susceptible to infection. This defect in host defence has generally been ascribed to the immaturity of neonatal immune cells; however, the degree of hyporesponsiveness is highly variable and depends on the stimulation conditions. These discordant responses illustrate the need for a more unified explanation for why immunity is compromised in neonates. Here we show that physiologically enriched CD71+ erythroid cells in neonatal mice and human cord blood have distinctive immunosuppressive properties. The production of innate immune protective cytokines by adult cells is diminished after transfer to neonatal mice or after co-culture with neonatal splenocytes. Neonatal CD71+ cells express the enzyme arginase-2, and arginase activity is essential for the immunosuppressive properties of these cells because molecular inhibition of this enzyme or supplementation with l-arginine overrides immunosuppression. In addition, the ablation of CD71+ cells in neonatal mice, or the decline in number of these cells as postnatal development progresses parallels the loss of suppression, and restored resistance to the perinatal pathogens Listeria monocytogenes and Escherichia coli. However, CD71+ cell-mediated susceptibility to infection is counterbalanced by CD71+ cell-mediated protection against aberrant immune cell activation in the intestine, where colonization with commensal microorganisms occurs swiftly after parturition. Conversely, circumventing such colonization by using antimicrobials or gnotobiotic germ-free mice overrides these protective benefits. Thus, CD71+ cells quench the excessive inflammation induced by abrupt colonization with commensal microorganisms after parturition. This finding challenges the idea that the susceptibility of neonates to infection reflects immune-cell-intrinsic defects and instead highlights processes that are developmentally more essential and inadvertently mitigate innate immune protection. We anticipate that these results will spark renewed investigation into the need for immunosuppression in neonates, as well as improved strategies for augmenting host defence in this vulnerable population. [ABSTRACT FROM AUTHOR]

NF-κB is a principal transcriptional regulator of diverse cytokine-mediated processes and is tightly controlled by the IκB kinase complex (IKK-α/β/γ). IKK-β and IKK-γ are critical for cytokine-induced NF-κB function, whereas IKK-α is thought to be involved in other regulatory pathways[SUP1-4]. However, recent data suggest a role for IKK-α in NF-κB-dependent gene expression in response to cytokine treatment[SUP1,5-7]. Here we demonstrate nuclear accumulation of IKK-α after cytokine exposure, suggesting a nuclear function for this protein. Consistent with this, chromatin immunoprecipitation (ChIP) assays reveal that IKK-α was recruited to the promoter regions of NF-κB-regulated genes on stimulation with tumour-necrosis factor-a. Notably, NF-κB-regulated gene expression is suppressed by the loss of IKK-α and this correlates with a complete loss of gene-specific phosphorylation of histone H3 on serine 10, a modification previously associated with positive gene expression. Furthermore, we show that IKK-α can directly phosphorylate histone H3 in vitro, suggesting a new substrate for this kinase. We propose that IKK-α is an essential regulator of NF-κB-dependent gene expression through control of promoter-associated histone phosphorylation after cytokine exposure. These findings provide additional insight into the role of the IKK complex in NF-κB-regulated gene expression. [ABSTRACT FROM AUTHOR]