الفهرس 
Immune SystemOnly 14 pages are availabe for public view
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Abstract
The development of the human immune system is not fully completed at the time of birth, but proceeds postnatally. Although the lymphocyte processes start in the early weeks of gestation, it takes months, even years after birth before full immune competencies achieved. Therefore, the fetal and neonatal immune system status changes rapidly and is difficult to evaluate.
The unique and still not completely understood immunological situation of the fetus as an allograft in utero complicates additionally the judgment of its immunological status based on data from later extra uterine life. The second distinct feature of the fetal immune development is the in utero protection from foreign antigens that could activate immunological reactions. Therefore, the immune system could be considered undeveloped and inexperienced at birth, and the consequence is higher neonatal susceptibility to infections, that is remarkable for low-gestation premature newborns.
Circulating inflammatory cells such as neutrophils, lymphocytes, monocytes, and natural killer cells express cell surface antigens, after activation by microbial products, which can be detected by flow cytometric technology. Several cell surface antigens have been identified to be promising in the detection of congenital sepsis, as well as early and late onset neonatal sepsis.
NK cells can perform antibody-dependent cellular cytotoxicity (ADCC) through CD16 or directly exert their cytotoxic ability by the release of perforin and granzyme B. NK cells also produce many cytokines such as interleukin (IL)-5, IL-10, IL-13, GM-CSF, TNF-α, TGF-β, and IFN-γ. IFN-γ can induce TH1 responses and also up-regulate MHC-I expression on antigen presenting cells. Recent pieces of evidence suggest the greater regulatory roles for NK cells by bridging innate with adaptive immunity via their intimate interactions with dendritic cells, B cells, and T cells.
Human NK cells can be divided into two major subsets based on CD56 expression: the CD56dim subset accounts for the majority (>90%) of peripheral blood NK cells that are more effective at mediating cytotoxic function, while the CD56bright CD16dim subset, characterized by the ability to produce immunoregulatory cytokines, constitutes only a minority (<10%) of the total NK cells.
Human neonates have comparable or higher numbers and percentages of NK (CD56+/CD16+/CD3−) cells in their peripheral blood compared to adults. Studies showed that the CD56−CD16+ subset NK cells are more abundant in the neonates and are precursors of the more mature CD56+CD16+ NK cells. The CD56bright and CD56dim NK cell subsets are present in similar proportions in neonatal blood and adult blood.
Thus, this study was conducted to evaluate the effect of prenatal dexamethasone on circulating Natural killer cells and expression of CD3, CD16-CD56 in neonatal circulation (for peripheral blood).
To elucidate our results, This case-control study was carried out on 50 preterm neonates in delivery Room at Menoufia University Hospitals after obtaining consent their parents and care givers.
All newborns randomly divided into two main groups, group I: included 25 newborns delivered to mothers who received dexamethasone throughout pregnancy which divided into two small groups: group 1A (n= 7 including preterms delivered to mothers who received one dose of dexamethasone) and group 1B (n =18 including preterms delivered to mothers who received two doses of dexamethasone) and group II: included 25 newborns delivered to mothers who didn’t receive dexamethasone throughout pregnancy matching the group 1 in gestational age,sex and birth weight.