Placental Transfer of Maternally-Derived IgA Precludes the Use of Guthrie Card Eluates as a Screening Tool for Primary Immunodeficiency Diseases

Abstract

There is a need for neonatal screening tools to improve the long-term clinical outcome of patients with primary immunodeficiency diseases (PID). Recently, a PCR-based screening method for both TRECs and KRECs using Guthrie card samples has been developed. However, the applicability of these excision circle assays is limited to patients with severe T or B cell lymphopenia (SCID, XLA and A-T), whereas the most common forms of PID are not detected. Absence of serum IgA is seen in a major fraction of patients with immunological defects. As serum IgA in newborns is considered to be of fetal origin, eluates from routinely collected dried blood spot samples might thus be suitable for identification of children with PID. To assess the applicability of such screening assays, stored Guthrie card samples were obtained from 47 patients with various forms of primary immunodeficiency diseases (SCID, XLA, A-T, HIGM and IgAD), 20 individuals with normal serum IgA levels born to IgA-deficient mothers and 51 matched healthy newborns. Surprisingly, normal serum IgA levels were found in all SCID, XLA, A-T and HIGM patients and, additionally, in all those IgAD patients born to IgA-sufficient mothers. Conversely, no serum IgA was found in any of the 16 IgAD patients born by IgA-deficient mothers. Moreover, half of the IgA-sufficient individuals born by IgA-deficient mothers also lacked IgA at birth whereas no IgA-deficient individuals were found among the controls. IgA in neonatal dried blood samples thus appears to be of both maternal and fetal origin and precludes its use as a reliable marker for neonatal screening of primary immunodeficiency diseases.

Locus-specific DNA methylation in the placenta is associated with levels of pro-inflammatory proteins in cord blood and they are both independently affected by maternal smoking during pregnancy

“…41 Immunoglobulin A and G (IgA and IgG) diffusion or active transport of maternal IgA to the child was observed during pregnancy through currently not fully appreciated mechanisms. 42 These phenomena might contribute to the observed differential methylation in cord blood after maternal smoking exposure, without necessarily interfering with the placentas methylome.…”

Detection of immunoglobulin isotypes from dried blood spots

“…Previously, only the four IgG isotypes (IgG1/2/3/4) were suggested to be transported through the placenta. The exclusive transport of the IgG subclasses from mother to infant has recently been challenged with the investigation of immunodeficient babies with maternal IgA (Borte et al, 2012). The quantities of each of the Ig isotypes, including the IgG subclasses, regardless of whether a portion of the Ig is from the mother, could provide clues about developing disorders or altered processes.…”

Simultaneous Quantification of T-Cell Receptor Excision Circles (TRECs) and K-Deleting Recombination Excision Circles (KRECs) by Real-time PCR.

“…The combined TRECs and KRECs assay can be also used to detect immunodeficiencies in newborn screening programs. In this case, the test must be performed on DNA extracted from small spots of blood blotted and dried on filter paper (Guthrie cards), must be highly sensitive and specific for the target diseases, as well as highly reproducible and cost-effective [10].…”