B cell subsets in thymus from infants with Down syndrome

ABSTRACT: B lymphocytes are still poorly characterized in the human thymus, and due to the immunological peculiarities of Down syndrome, a detailed investigation of thymic B lymphocytes and their subsets was performed in <2-year-old infants. This is a period of intense thymic activity, and here we compared thymuses from infants with Down syndrome (DG) and age-matched control group (CG) with heart disease as the only described malformation, no clinical signs of immunodeficiency and normal blood lymphocyte numbers. METHODS: This study, approved by the institutional ethics committee, included 10 thymic samples from DG infants, and 20 from CG infants. Depending on thymus size and the type of surgical approach, babies were submitted to total thymectomy or only the removal of a small thymic fragment (mainly in the DG), always during cardiac surgery in order to correct congenital defects. Flow cytometry was used for immunophenotyping of cell suspension obtained from thymic tissue; and the B lymphocyte topographic localization was investigated by immunohistochemistry, and a quantitative evaluation of B-cells in each region was carried out using methods of digitized images analysis. RESULTS: Flow cytometry revealed that CD20+ cells represent around 1% of total lymphocytes in both groups, with higher naive and lower unswitched memory B lymphocyte frequencies in DG when compared to the CG, while B1 cells were present in much higher frequency in DG than in CG. All the other B-cell subpopulations (transitional, switched memory, plasmablasts and plasmocytes) were statistically equivalent between groups. Immunohistochemistry showed higher frequencies of CD20+ cells in medullary region compared to cortex, without differences between the groups (DG = 16.8% and CG = 17.1% of total cell number), while the cortex region had few B cells in both groups, with significantly lower frequency in DG group, reaching 0.25%, compared with the CG, which showed 0.6%. CONCLUSION: Flow cytometry revealed a different distribution of B-cell subtypes in DG thymus compared to CG and, thus, data obtained from such rare material could be relevant in the characterization and further analysis and understanding of the immunological mechanisms that involve the participation of B lymphocyte subpopulations in the thymus. FAPESP (grant 2014/50489-9).

TLR expression, phagocytosis and oxidative burst in healthy and septic newborns in response to Gram-negative and Gram-positive rods.

The objective was to investigate whether phagocytes from healthy and septic newborns have a developmental deficiency in their capacity to recognize, phagocytize and generate hydrogen peroxide (H2O2) in response to Escherichia coli and Staphylococcus aureus. TLR expression and phagocytic ability of neutrophils and monocytes from 44 healthy preterm and term neonates, from 13 newborns with late-onset sepsis and from 24 healthy adults were determined using flow cytometry, and H2O2 production was measured by dihydrorhodamine test. TLR-2 and TLR-4 expressions were similar among the groups. The phagocytic ability of monocytes and neutrophils exposed to E. coli and S. aureus in healthy and septic neonates was significantly reduced compared to that of adults. Monocytes from septic newborns exposed to E. coli had higher H2O2 production than those of the other groups. The oxidative burst of monocytes exposed to S. aureus was reduced in preterm newborns compared with term ones and those with sepsis, and no differences were found in the oxidative burst of neutrophils. Even with the ability to recognize bacteria, a decreased clearance of pathogens can cause an imbalance in the immune response, which could lead to a predisposition to sepsis. Once established, the increased production of cytokines and ROS in an attempt to control the infection as well as the lack of full phagocytic activity leads to persistence of the pathogen and a state of constant inflammation.

IgG placental transfer in healthy and pathological pregnancies.

Placental transfer of maternal IgG antibodies to the fetus is an important mechanism that provides protection to the infant while his/her humoral response is inefficient. IgG is the only antibody class that significantly crosses the human placenta. This crossing is mediated by FcRn expressed on syncytiotrophoblast cells. There is evidence that IgG transfer depends on the following: (i) maternal levels of total IgG and specific antibodies, (ii) gestational age, (iii) placental integrity, (iv) IgG subclass, and (v) nature of antigen, being more intense for thymus-dependent ones. These features represent the basis for maternal immunization strategies aimed at protecting newborns against neonatal and infantile infectious diseases. In some situations, such as mothers with primary immunodeficiencies, exogenous IgG acquired by intravenous immunoglobulin therapy crosses the placenta in similar patterns to endogenous immunoglobulins and may also protect the offspring from infections in early life. Inversely, harmful autoantibodies may cross the placenta and cause transitory autoimmune disease in the neonate.

Preterm and term neonates transplacentally acquire IgG antibodies specific to LPS from Klebsiella pneumoniae, Escherichia coli and Pseudomonas aeruginosa.

High incidences of Gram-negative bacteria are found in neonatal nosocomial infections. Our aim was to investigate placental transmission of immunoglobulin G (IgG) reactive with lipopolysaccharide from Klebsiella pneumoniae, Pseudomonas aeruginosa and Escherichia coli O111, O6 and O26. The total and lipopolysaccharide-specific IgM and IgG were determined in 11 maternal/umbilical-cord sera aged ≤33 weeks (GI); 21 aged >33 and <37 weeks (GII); and 32 term newborns (GIII). The total and lipopolysaccharide-specific IgM concentrations were equivalent in maternal sera. The total IgG concentrations were equivalent in maternal and newborn sera, with the exception of GIII newborns as compared with their mothers (P<0.0001) and with neonates from GI and GII (P<0.05). Lipopolysaccharide-specific IgG concentrations were lower in GI neonates than in their mothers (P<0.01) and lower in GII (P<0.05). Lower lipopolysaccharide-specific IgG levels were observed among neonates only for O111 in GI (P<0.05) and for O26 and Pseudomonas in GII, both as compared with GIII (P<0.05). The anti-lipopolysaccharide IgG transfer ratios were lower in GI (except for O26) and in GII (except for Klebsiella and O111) as compared with GIII (P<0.05). Our results suggest that the greater susceptibility to infections in preterm infants is influenced (besides the humoral response) by factors intrinsic and extrinsic to the condition of prematurity.