Background: Our previous study showed an association between increased concentration of endotoxin in house dust and elevated IFN-gamma responses in neonates. The impact of other microbial agents on immune responses in infancy is poorly known.
Objective: To examine whether stimulated cytokine responses of mothers and their children are associated with concentrations of other microbial markers in addition to endotoxin in house dust samples.
Methods: Mitogen-stimulated production of IFN-gamma, IL-4, IL-6 and TNF-alpha was measured in cord blood and in peripheral blood of mothers (n=29) and their children (n=29) 3 months after birth. Gas chromatography mass spectrometric analysis was applied to measure the concentrations of ergosterol (marker of fungal biomass), muramic acid (indicating the presence of Gram-positive bacteria) and 3-hydroxy fatty acids (C(10:0)-C(14:0), indicating the presence of Gram-negative bacteria) in house dust. Endotoxin was determined with Limulus assay.
Results: Significant mother-to-child correlations were observed in stimulated production of TNF-alpha and IL-6 3 months after birth. 3-hydroxy fatty acid (C(10:0)-C(14:0)) levels in bed dust were inversely associated with the production of TNF-alpha and IL-6 in blood samples of mothers and their 3-month-old children. High concentrations of muramic acid in floor dust were related to increased production of TNF-alpha and IL-6 at the age of 3 months. In contrast to endotoxin, none of the other microbial markers were significantly associated with enhanced IFN-gamma-producing capacity from birth to 3 months.
Conclusions: Exposure to Gram-negative bacteria and their components may be associated with down-regulated immune responses in early infancy, indicated as an impaired production of pro-inflammatory cytokines following mitogen stimulation. Gram-positive bacteria and their constituents seem to have opposite effects. Of the measured markers, exposure to bioactive endotoxin appears to have the strongest impact on T-helper type 1 responses.