The main peculiarities of neonatal immune system are:
- The prevalence of immature CD5+ B-lymphocytes with high expression of slgM and lack of slgD which are able to produce polyreactive IgM, IgG1 and IgG3; massive antigen binding with slgM leads to immature B-cell apoptosis.
- Low expression of CD40L on neonatal T-lymphocytes decreases their ability to differentiate to Th1 and to intensify macrophage reactions, to cooperate with B-cells and to be typically switch immunoglobulin classes synthesis.
- Insufficiency of B7 expression on antigen-presenting cells (APC) which leads to non-professional antigen presentation to naive T-cells. Ratio of professional and non-professional APC has influence on priming or tolerance as a result of neonatal immune response. Small amounts of antigen can interact with a few mature B-cells and can be a base for specific humeral immunity development.
- Heterogeneity of CD4+ lymphocyte subpopulation, the priority of CD45RA+ naive T-cells which act as suppression inductors and produce mainly interleukin-2.
The aim of our research work was to investigate dynamical changes of main immunological parameters (such as IL-I, TNF-α, IL-4, TGF-β serum concentrations (ELISA), lymphocyte phenotype (flow cytometry) and chemiluminescent response of peripheral blood phagocytes) during the early postnatal period in physiological conditions and in infants suffered from respiratory distress-syndrome (RDS) or pneumonia. We investigated 48 full-term newborn infants from moderate and high risk pregnancies during the first month of life.
It was found that serum levels of IL-lβ in cord blood of healthy neonates from moderate risk pregnancies were significantly higher than in peripheral blood of healthy adults (491,4±49,9 pg/ml versus 277,5±64,4 pg/ml respectively; p<0,05) but IL-4 serum concentrations in cord blood were significantly lower than those in blood of adults (27,4±10,2 pg/ml versus 126,3±27,2 pg/ml respectively, p<0,05).
During the first week of life in physiological conditions serum levels of proinflammatory cytokines and IL-4 significantly increased in comparison with cord blood levels. CD3+ and CD4+ cell numbers had the same dynamics while the number of CD8+ cytotoxic T-lymphocytes significantly decreased. The level of zymozan-induced chemiluminescence of peripheral blood leukocytes became significantly lower till the 7th day of life in comparison with cord blood. The values of immunological parameters under the physiological conditions were different from those situations when early postnatal period was complicated with respiratory distress-syndrome (RDS) or pneumonia (significantly lower serum levels of IL-I and TNF, reduced absolute numbers of CD3+, CD4+, CD8+ and B-cells. significantly higher level of spontaneous chemiluminescence in peripheral blood of neonates suffered from RDS or pneumonia versus healthy infants on the 5th-7th day of life. Recovery from pneumonia or RDS was accompanied with restoration of pro- and anti-inflammatory cytokine balance, elevation of absolute lymphocyte number and serum IgM level, reduction of natural killer number and level of expression of CD25+ receptor to IL-2 as well as normalization of spontaneous CL level.
So we describe the mode of normal early postnatal immunological adaptation in healthy full-term newborn infants and immunological distress-syndrome in neonates with RDS or pneumonia. The data are important for the further decisions concerning immunological intervention in neonatal period.
The work is submitted to Scientific Conference "Basic and applied research", Brazil (Rio de Janeiro), February 19 - March 3, 2009. Came to the Editor´s Office on 22.12.2008.