Sanne Hoeks

Chapter 1 14 per individual cell are produced. 27 Natural killer (NK) cells have a poor cytotoxicity, due to absence of adequate levels of activating cytokines. Neutrophils have a reduced chemotactic ability and a decreased capacity for adherence and extravasation from the bloodstream. 28 Moreover, functional assays have shown that the complement system exhibits at birth lower opsonizing capacity, relatively impaired chemotaxis and reduced lytic function. 29, 30 To help initial immune responses, evolutionary conserved mechanisms like the production of superoxide are employed for effectively assisting in bacterial killing. Furthermore, neonates have obtained maternal immunoglobulins (Ig): transplacental transported IgG in the last trimester of pregnancy and maternal IgA secreted in human milk. However, these systems are not always sufficient enough to compensate for the ineffectiveness of the neonatal innate immune system to fight infections. Perinatal characteristics of immunological responses are summarized in figure 3.