The immune system in newborns

Babies are very prone to infections as their immune system has not fully matured. This immaturity could potentially be attributed to qualitative and/or quantitative differences between neonatal and adult immune cells.

B lymphocytes are an immune cell type that primarily generate antigen-specific antibodies, but can also serve as antigen-presenting cells, secreting cytokines. Evidence from experimental models indicates that during maturation, B cells possess different and very distinct functional characteristics. Cord blood phenotypic analysis has indicated that the majority of B cells are transitional with very few mature cells. However, it remains controversial if these phenotypic characteristics are indicative of functional immaturity.

In this context, the EU-funded 'Functional analysis of the neonatal B cell compartment' (NEONATAL B CELLS) project wished to understand the functional differences between the neonatal and adult B cell compartments by analysing the mechanisms that contribute to this phenomenon. For this purpose, scientists analysed B cell subpopulations from neonates and adults with respect to signalling, activation, production of immunoglobulins and cytokines.

Project results indicated no phenotypic differences, but a significantly reduced response to various immune stimuli. Importantly, neonatal B cells only produced the basic IgM immunoglobulins and were incapable of antibody class switching, a property of mature B cells. Certain signalling pathways were also altered in neonatal B cells, further supporting the hypothesis regarding their immaturity. Ongoing molecular analysis of these cells will unveil the mechanisms underlying this functional immaturity.

Collectively, these findings significantly enhance our understanding of the immune system in newborns and how it matures during development. Implementation of this information in clinical practice could help improve the therapy and prevention of infections not only in newborns, but also in preterm babies.