Objective The aims of this study were to investigate activin-A expression in the peripheral blood of neonates with nosocomial infection and monocytes and lymphocytes following stimulation in vitro.

Methods 37 infected neonates were studied: 16 with birth weights <1500 g, 11 with birth weights 1500–2800 g and 10 with birth weights >2800 g. 37 healthy neonates were used as controls. Peripheral blood samples were obtained on the 1st, 3rd and 5th days after infection. Purified monocytes and lymphocytes were stimulated with lipopolysaccharide or phytohaemagglutin, respectively. Cytokine levels were measured in serum and culture supernatants by ELISA.

Results Neonates with birth weights <1500 g had significantly increased activin-A levels on the 1st, 3rd and 5th days. Neonates with birth weights 1500–2800 g had significantly increased activin-A levels on the 5th day. In contrast, levels of the pro-inflammatory cytokine IL-8 were increased mainly in neonates with birth weights >1500 g. Stimulation of lymphocytes and monocytes resulted in significantly increased activin-A at 48 h. However, tumour necrosis factor alpha levels in activated lymphocytes were increased at 18 h, whereas in monocytes they were increased at 4 h.

Conclusion Activin-A is increased in peripheral blood following nosocomial infection and specifically in premature neonates. Lymphocytes and monocytes produce activin-A following stimulation, pointing to these cells as the main source of activin-A in neonatal blood. Ongoing studies will elucidate the possible pro or anti-inflammatory role of activin-A in neonatal infections.