Neonatal bacterial sepsis is often characterized by a fulminant clinical course and highly elevated plasma levels of proinflammatory cytokines. To evaluate in vitro activation of the neonatal immune system by specific infectious stimuli, cord blood cells from healthy neonates were examined for expression of tumor necrosis factor-alpha (TNF-alpha), IL-1beta, IL-6, and IL-8 in response to Streptococcus agalactiae (GBS), lipopolysaccharide (LPS), and lipoteichoic acid (LTA). Cytokine-expression was compared in mononuclear cells from cord and adult peripheral blood. TNF-alpha and IL-6 levels in the supernatant of cord blood cell cultures were significantly higher after stimulation with heat-killed GBS (10(7)/mL) than with LPS (2 microg/mL) or LTA (2 microg/mL) (TNF-alpha: 2215 versus 267.5 versus 40 pg/mL, p = 0.001; IL-6: 9667 versus 4909 versus 919 pg/mL, p = 0.006). mRNA expression of TNF-alpha, IL-1beta, IL-6, and IL-8 was equally pronounced after stimulation with either GBS, LPS, or LTA in cord or adult blood cells at various times. A MAb directed against the monocyte receptor molecule CD14 did not inhibit the release of cytokines in cord blood mononuclear cells after stimulation with GBS. In summary, activation of cord blood cells by infectious stimuli is comparable to the adult immune response in terms of expression of proinflammatory cytokines. GBS in particular proves to be a potent activator of the neonatal immune system when compared with LPS and LTA. CD14 seems not to be a crucial molecule for activation of cord blood cells by GBS.