Functional studies on Fc receptors

Transfer of Maternal Antimicrobial Immunity to HIV-Exposed Uninfected Newborns

The transfer of maternal immune factors to the newborn is critical for protection from infectious disease in early life. Maternally acquired passive immunity provides protection until the infant is beyond early life's increased susceptibility to severe infections or until active immunity is achieved following infant's primary immunization. However, as reviewed here, human immunodeficiency virus (HIV) infection alters the transfer of immune factors from HIV-infected mothers to the HIV-exposed newborns and young infants. This may relate to the immune activation in HIV-infected pregnant women, associated with the production of inflammatory cytokines at the maternofetal interface associated with inflammatory responses in the newborn. We also summarize mother-targeting interventions to improve the health of infants born to HIV-infected women, such as immunization during pregnancy and reduction of maternal inflammation. Maternal immunization offers the potential to compensate for the decreased transplacentally transferred maternal antibodies observed in HIV-exposed infants. Current data suggest reduced immunogenicity of vaccines in HIV-infected pregnant women, possibly reducing the protective impact of maternal immunization for HIV-exposed infants. Fortunately, levels of antibodies appear preserved in the breast milk of HIV-infected women, which supports the recommendation to breast-feed during antiretroviral treatment to protect HIV-exposed infants.

Transplacental transport of IgG antibodies to preterm infants: a review of the literature

Newborn infants, especially preterm infants, have an immature immune system, which is not capable to actively protect against vaccine-preventable infections. Therefore, the newborn is dependent on transplacental transport of Immunoglobulin G (IgG), an active, FcRn receptor mediated process. Fetal IgG rises from approximately 10% of the maternal concentration at 17-22weeks of gestation to 50% at 28-32weeks of gestation. If transplacental acquired IgG is lower in preterm than in term infants, preterm infants are especially at risk for these vaccine-preventable diseases. The aim of this study was to review the transplacental transfer of IgG against vaccine-preventable diseases (measles, rubella, varicella-zoster, mumps, Haemophilus influenza type B, diphtheria, tetanus, pertussis and polio) to (pre)term infants and to identify factors that influence the transplacental transfer of these antigens. After selection, 18 studies on transplacental transport to preterm infants were included. In general, these studies showed for all antibodies that preterm infants have lower antibody concentrations compared with term infants. Maternal and infants antibody concentrations showed a strong correlation in 7 of the included studies. Infant antibody concentration was not associated with parity, maternal age, height or weight. Infants of vaccinated mothers had lower anti-measles antibody titers than infants of natural immunized mothers. IgG titers of preterm infants decrease earlier in life below protective antibody titers than term infants. Combined with their immature immune system, this puts preterm infants at increased risk for vaccine-preventable diseases.

Use of the DAF assay to assess the functional properties of polyclonal and monoclonal RhD antibodies

The mechanism whereby passive Rh (D) immunoglobulins suppress the fetomaternal alloimmunization is still unclear. New in vitro tests are needed to better characterize the functional properties of polyclonal anti-Ds. The DAF assay was developed to monitor the antibody-dependent cell-mediated cytotoxicity (ADCC) and the phagocytosis of anti-Rh (D)-sensitized RBCs by effector cells. The principle of this test is based on the oxydization of the 2,7-diaminofluorene (DAF) by the pseudoperoxidase activity of free hemoglobin. The reaction is proportional to the hemoglobin concentration. This test was performed to determine and emphasize the efficacy of different polyclonal anti-D immunoglobulin preparations to mediate lysis and phagocytosis of sensitized RBCs by human peripheral mononuclear cells. The functional properties of different human RhD monoclonal antibodies were also analyzed and compared. The test was found to be convenient to perform and allowed the avoidance of radioactive labelling of RBCs for ADCC studies. It is mainly useful for the direct quantitation of phagocytosis.