Patricia Palmeira

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.

Transfer of antibodies across the placenta and in breast milk from mothers on intravenous immunoglobulin

We studied the levels of immunoglobulins in colostrum, milk and sera from two common variable immunodeficiency (CVID) mothers (M1 and M2), and in sera from their newborn infants. During pregnancy they continued intravenous immunoglobulin therapy (IVIG). Antibody levels from maternal and cord blood collected at delivery and colostrum and milk, collected on the 3rd and 7th post‐partum days, respectively, were analyzed. Although cord/maternal blood ratios of total immunoglobulins and subclasses, as well as specific antibodies differed between M1 and M2, both showed good placental transfer of anti‐protein and anti‐polysaccharide antibodies, despite lower cord/maternal blood ratios in M2. Anti‐Streptococcus pneumoniae antibody avidity indexes were similar between paired maternal and cord serum. Both mothers’ colostrum and milk samples showed only traces of IgA, and IgM and IgG levels in colostrum were within normal range in M1, whereas M2 presented elevated IgG and low IgM levels, when compared with healthy mothers. The study of colostrum and milk activity showed that they strongly inhibited enteropathogenic Escherichia coli adhesion in vitro. CVID patients must be informed about the relevance of regular IVIG administration during pregnancy, not only for their own health but also for their immune immature offspring. Breast‐feeding should be encouraged as colostra from these CVID patients strongly inhibited E. coli adhesion to human epithelial cells thus providing immunological protection plus nutritional and psychological benefits for the infant.

Inhibition of enteropathogenic Escherichia coli adhesion to HEp-2 cells by colostrum and milk from mothers delivering low-birth-weight neonates

Abstract Breast milk samples from three groups of Brazilian women were evaluated for their inhibitory effect on enteropathogenic Escherichia coli (EPEC) adhesion to HEp-2 cells: G1, mothers delivering preterm babies of appropriate birth weight (n = 12); G2, mothers delivering term babies of low birth weight (n = 11); G3, the control group, mothers delivering term babies of appropriate birth weight (n = 39). Colostrum samples were obtained at 48–72 h and milk samples on the 7th, 30th and 60th days after delivery. All samples showed strong inhibitory activity (66%–100%), without significant differences among the three groups and four periods. Total IgA and anti-EPEC IgA concentrations were significantly higher in colostrum than in milk samples in the three groups studied. The levels of colostral IgA and anti-EPEC IgA observed in G1 and G2 were significantly higher compared to the control group. Western blotting assays showed that individual samples as well as pools of colostrum or milk samples contain IgA antibodies to many EPEC outer membrane proteins. A 94 kDa band with molecular weight consistent with the EPEC adhesin named intimin, was recognized by all samples analysed. Bands of different molecular weight were also recognized by some samples of colostrum and milk, such as a band of ∼ 18.4 kDa, with molecular weight equivalent to bundle-forming pilus subunits. Conclusion Our results suggest that colostrum and milk from mothers of premature and small-for-date term neonates are as effective in protecting the newborn against EPEC infections as those from mothers of term babies of appropriate birth weight.

Mother to child transfer of IgG and IgA antibodies against Dermatophagoides pteronyssinus.

There is strong evidence from animal models that placental and/or breast milk‐mediated transfer of maternal allergen‐specific IgG prevents allergic immune responses in the progeny. Both human and animal data also point to IgA as having an important regulatory role. In contrast, little is known about maternal transfer of IgG and IgA specific for respiratory allergens in humans. Dermatophagoides pteronyssinus (Der p) is an indoor allergen that is a major cause of asthma worldwide. We analysed maternal to child Der p‐specific IgG and IgA transfer in a cohort of 77 paired maternal and child samples. We found Der p‐specific IgG and its IgG1, IgG2 and IgG4 subclasses in all cord blood samples. Except for IgG1, cord levels were higher in newborns from atopic mothers (n = 29) compared to non‐atopic mothers (n = 48). Der p‐specific IgA was found in all colostrum samples and levels were independent of maternal atopic status. Notably, anti‐Der p IgG was also found in colostrum and levels were higher in atopic mothers. We believe that our work is a critical first step in the identification of early factors that may impact asthma development and should guide the development of clinical studies that assess whether Der p‐specific IgG and IgA protect children from allergy as demonstrated in animal models.

Passive Acquisition of Protective Antibodies Reactive with Bordetella pertussis in Newborns via Placental Transfer and Breast-feeding

Although acquisition of anti‐pertussis antibodies by the newborn via placental transfer has been demonstrated, a subsequent recrudescence of pertussis infection is often observed, particularly in infants. The present study investigated the passive transfer of anti‐pertussis IgG and IgA antibodies to term newborns and their ability to neutralize bacterial pathogenicity in an in vivo experimental model using mice intracerebrally challenged with viable Bordetella pertussis. Forty paired samples of maternal/umbilical cord sera and colostrum were obtained. Anti‐pertussis antibodies were analysed by immunoenzymatic assay and by Immunoblotting. Antibody neutralizing ability was assessed through intracerebral B. pertussis challenges in mice. Anti‐pertussis IgG titres were equivalent in both maternal and newborn sera (medians = 1:225 and 1:265), with a transfer rate of 118%. The colostrum samples had variable specific IgA titres (median = 1:74). The immunoblotting assays demonstrated identical recognition profiles of paired maternal and newborn serum pools but different bacterial recognition intensities by colostrum pools. In the animal model, significant differences were always observed when the serum and colostrum samples and pools were compared with the positive control (P < 0.05). Unlike samples with lower anti‐pertussis titres, samples with high titres showed protective capacities above 50%. Pertussis‐absorbed serum and colostrum pools protected 30% of mice and purified IgG antibodies protected 65%. Both pooled and single‐sample protective abilities were correlated with antibody titres (P < 0.01). Our data demonstrated the effectiveness of anti‐pertussis antibodies in bacterial pathogenesis neutralization, emphasizing the importance of placental transfer and breast‐feeding in protecting infants against respiratory infections caused by Bordetella pertussis.

Passive immunity acquisition of maternal anti-enterohemorrhagic Escherichia coli (EHEC) O157:H7 IgG antibodies by the newborn

Enterohaemorrhagic Escherichia coli (EHEC) strains are among the main causes of haemorrhagic colitis (HC) and haemolytic-uremic syndrome (HUS) in industrialised countries. In Brazil, EHEC have been detected in the faeces of patients with non-bloody diarrhoea, though an association between EHEC and HUS has been detected recently. These observations suggest that there is a pre-existing immunity triggered by the contact with EHEC and other categories of bacteria, such as EPEC, that share similar virulence factors and to which our population is highly exposed. Our aim was to evaluate the placental transfer of IgG antibodies reactive to EHEC O157:H7 antigens. We evaluated 28 paired maternal and cord sera for the presence of IgG against EHEC O157:H7 protein antigens and IgG and IgM to O157 LPS employing ELISA and IB technique. Total IgG and IgM level analyses were also made. Anti-EHEC O157:H7 and anti-LPS O157 IgG antibody levels in cord sera were equivalent to those of their maternal sera. A good correlation between the mothers’ anti-LPS O157 IgM and total IgM levels was found. Anti-LPS O157 IgM levels were higher than anti-LPS O157 IgG levels in the same samples, and anti-LPS IgM antibodies were not detected in cord sera. Identical patterns of recognition of bacterial protein antigens by specific IgG were found in the paired samples and the recombinant purified variable region of γ intimin was specifically recognized by one paired maternal and cord sample. In conclusion, although the antibody profile varied among individuals, all paired cord and maternal serum samples showed an identical recognition pattern, indicating an efficient placental transfer of IgG antibodies reactive to EHEC O157:H7 antigens.

Phenotypic Differences in Leucocyte Populations among Healthy Preterm and Full‐Term Newborns

The immune system of neonates has been considered functionally immature, and due to their high susceptibility to infections, the aim of this study was to analyse the phenotypic differences in leucocyte populations in healthy preterm and full‐term newborns. We evaluated the absolute numbers and frequencies of dendritic cells (DCs) and DC subsets, monocytes and T and B lymphocytes and subsets in the cord blood of healthy moderate and very preterm (Group 1), late preterm (Group 2) and full‐term (Group 3) newborns and in healthy adults, as controls, by flow cytometry. The analyses revealed statistically higher absolute cell numbers in neonates compared with adults due to the characteristic leucocytosis of neonates. We observed a lower frequency of CD80+ myeloid and plasmacytoid DCs in Group 1 and reduced expression of TLR‐4 on myeloid DCs in all neonates compared with adults. TLR‐2+ monocytes were reduced in Group 1 compared with Groups 2 and 3, and TLR‐4+ monocytes were reduced in Groups 1 and 2 compared with Group 3. The frequencies and numbers of naïve CD4+ T and CD19+ B cells were higher in the three groups of neonates compared with adults, while CD4+ effector and effector memory T cells and CD19+ memory B cells were elevated in adults compared with neonates, as expected. Our study provides reference values for leucocytes in cord blood from term and preterm newborns, which may facilitate the identification of immunological deficiencies in protection against extracellular pathogens.

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.

Immunology of breast milk.

In the critical phase of immunological immaturity of the newborn, particularly for the immune system of mucous membranes, infants receive large amounts of bioactive components through colostrum and breast milk. Colostrum is the most potent natural immune booster known to science. Breastfeeding protects infants against infections mainly via secretory IgA (SIgA) antibodies, but also via other various bioactive factors. It is striking that the defense factors of human milk function without causing inflammation; some components are even anti-inflammatory. Protection against infections has been well evidenced during lactation against, e.g., acute and prolonged diarrhea, respiratory tract infections, including otitis media, urinary tract infection, neonatal septicemia, and necrotizing enterocolitis. The milks immunity content changes over time. In the early stages of lactation, IgA, anti-inflammatory factors and, more likely, immunologically active cells provide additional support for the immature immune system of the neonate. After this period, breast milk continues to adapt extraordinarily to the infants ontogeny and needs regarding immune protection and nutrition. The need to encourage breastfeeding is therefore justifiable, at least during the first 6 months of life, when the infants secretory IgA production is insignificant.

Systemic Antibody Response to Diarrheagenic Escherichia coli and LPS O111, O157 and O55 in Healthy Brazilian Adults

Enterohaemorrhagic Escherichia coli (EHEC) can cause a variety of human illnesses ranging from uncomplicated diarrhoea to haemorrhagic colitis and haemolytic uremic syndrome. The serotype O157:H7 has been associated with numerous outbreaks worldwide, but in Brazil the infection is rare. Brazilian adults present antibodies reactive with the principal virulence factors of enteropathogenic E. coli (EPEC) that have many genetic and antigenic similarities with EHEC. Lipopolysaccharides (LPS) are components of outer membranes and important virulence factors of Gram‐negative bacteria. LPS O111 is present in EPEC and EHEC strains. LPS O157 is found only in EHEC strains, but it has some structural similarities with LPS O55 present in EPEC strains. This study investigates the levels of IgG and IgM seric antibodies reactive with EHEC O157:H7, EHEC O111:H–, EPEC O111:H– and the levels of anti‐LPS O111, LPS O157 and LPS O55 antibodies in healthy adults living in São Paulo, Brazil. The antibody levels were determined by an enzyme‐linked immunosorbent assay for 100 individual serum samples, and the presence of anti‐bacterial and anti‐LPS seric antibodies was confirmed. Positive correlations were found among the three kinds of antibodies. The concentrations of IgM anti‐LPS were significantly higher than those of IgG, and surprisingly, the concentrations of anti‐LPS O157 were high in view of the infrequent isolation of O157 bacteria in Brazil. Our results suggest that there is a cross‐reacting immunity to EHEC in the Brazilian population, which may be a result of the immunity to EPEC antigens. Alternatively, Brazilians may be exposed to EHEC more frequently than has previously been thought.