Haematopoiesis in term and preterm neonates is developmentally immature compared with adults. Thus, in neonates the number of myeloid cells are reduced, the function of phagocytes and lymphocytes are deficient and the levels of most immunoglobulin classes, complement components and fibronectin are very low. Bacterial infections further depress host defence mechanisms of the newborn and that explains the high morbidity and mortality caused by them.

In order to reduce neonatal morbidity and mortality due to infections ways to enhance neonatal host defence mechanisms have been tried during the last years. The most commonly used procedure is the administration of I.V.I.G. It has been shown that IVIG apart from increasing serum opsonic activity have other immunomodulatory effects as i.e. antiinflammatory properties. Clinical studies, performed to find out whether IVIG can protect neonates from infection, showed contradicting results. Possibly the antibody levels against the most common neonatal pathogens were very low in the IVIG batches used in the unsuccessful studies. The studies that evaluated I.V.I.G. treatment for neonatal septicaemia are very few, however they give promising results.

Because of reduced neutrophil storage pools neonates tend to develop neutropenia during bacterial sepsis. Colony stimulating factors CG-CSF and GM-CSF could improve resistence to infection in septicaemic neonates by a) improving neutrophil production and b) improving of neutrophil - macrophage function.

In experimental animals the administration of G-CSF or CM-CSF caused reduction of the mortality due to sepsis. In human septicaemic neonates CSF's increased neutrophil production and upregulated their chemotaxis, oxidative metabolism phagocytosis, C3b1, receptor expression and antibody dependent cytotoxicity.

The studies regarding administration of CSF in human neonates are very few and trials regarding their administration during neonatal sepsis should be given priority.

Finally, the simultaneous administration of a) I.V.I.G. with high antibody titers against common neonatal pathogens and b) of G-CSF or GM-CSF should be tried during overwhelming neonatal septicaemia in order to further enhance host defence mechanisms of the newborn.