Herpes simplex virus-stimulated gamma-interferon production by newborn mononuclear cells

Dysregulated Mucosal Immunity and Associated Pathogeneses in Preterm Neonates

Many functions of the immune system are impaired in neonates, allowing vulnerability to serious bacterial, viral and fungal infections which would otherwise not be pathogenic to mature individuals. This vulnerability is exacerbated in compromised newborns such as premature neonates and those who have undergone surgery or who require care in an intensive care unit. Higher susceptibility of preterm neonates to infections is associated with delayed immune system maturation, with deficiencies present in both the innate and adaptive immune components. Here, we review recent insights into early life immunity, and highlight features associated with compromised newborns, given the challenges of studying neonatal immunity in compromised neonates due to the transient nature of this period of life, and logistical and ethical obstacles posed by undertaking studies newborns and infants. Finally, we highlight how the unique immunological characteristics of the premature host play key roles in the pathogenesis of diseases that are unique to this population, including necrotizing enterocolitis and the associated sequalae of lung and brain injury.

Reduced primary antigen-specific T-cell precursor frequencies in neonates is associated with deficient interleukin-2 production

Clinical evidence has indicated that the neonatal cell-mediated immune response to primary infection is delayed when compared to that of adults with the same primary infection. The mechanisms regulating the development of antigen-specific T-cell immunity in neonates remain to be elucidated. We examined the primary immune response to the non-recall antigen, keyhole limpet haemocyanin (KLH) in adults and neonates in vitro. We report here that conventional bulk culture methods show reduced proliferative responses in neonates although statistical significance was not achieved. Using limiting dilution analysis, the frequencies of KLH-specific T lymphocytes were 10-100-fold lower in neonates when compared to adults. Interleukin-2 (IL-2) production was significantly lower in the supernatants of neonatal mononuclear cells (MNC) stimulated with KLH when compared to adults. Addition of exogenous IL-2 increased precursor frequencies twofold in both adult and newborn cultures. In contrast to the secreted IL-2 levels, IL-2 mRNA expression was higher in antigen-stimulated neonatal MNC preparations, even though proliferation was lower. These observations indicate differential in vitro responsiveness in neonates and adults to primary antigenic challenge. Since no IL-2 was detected in cell lysates, the presence of high levels of IL-2 mRNA and low IL-2 production suggests inability by neonatal MNC to translate IL-2. This deficiency in IL-2 production may explain the reduced precursor frequencies, suggesting failure to recruit T lymphocytes in order to expand the KLH-specific T-cell response. These observations are important for the understanding of the development of primary immune responses and immunological maturation in neonates.

Interleukin-1 augments the diminished interleukin-2 mRNA expression and proliferative response of neonatal T lymphocytes to anti-CD2 antibodies

Expression of IL-2 mRNA by unstimulated and stimulated purified T cells and mononuclear cells from adult and cord blood was investigated in an attempt to better understand the underlying defective neonatal host immune defense system. Using RNA dot-blot analysis, IL-2 mRNA expression in anti-CD2-stimulated neonatal T cells revealed significantly reduced levels when compared to adult T cells (P < 0.01). Purified neonatal T cells also showed a significantly reduced proliferative response to anti-CD2 antibodies (P < 0.01). Addition of IL-1 beta enhanced the hyporesponsiveness of neonatal T cells at both the level of proliferation and IL-2 mRNA expression. Unseparated mononuclear cells from adult and cord blood revealed similar IL-2 mRNA levels and proliferation when activated by anti-CD2 stimulation. The reduced IL-2 mRNA expression observed in neonatal T cells may explain, in part, the difference in host defense between the newborn and adult during states of increased demand such as infection.