Cord blood molecular biomarkers of eosinophilopoiesis: Kinetic analysis of GATA-1, MBP1 and IL-5Rα mRNA expression

Abstract

Eosinophil/basophil (Eo/B) progenitor phenotype and function in cord blood (CB) are associated with atopic risk at birth and infant clinical outcomes. Molecular analyses of eosinophil-basophil differentiation events could identify clinically predictive biomarkers. To determine CB kinetic patterns of Eo/B lineage-associated gene expression (GATA-1, MBP1 and IL-5R alpha) after IL-5 stimulation, CB non-adherent mononuclear cells were isolated from random fresh and frozen samples and incubated in the presence of recombinant human interleukin-5. Some underwent CD34+ positive selection using magnetic cell separation. At various time-points, mRNA expression of GATA-1, MBP1 and IL-5R alpha (total transcripts) was determined utilizing multiplex quantitative polymerase chain reaction (Q-PCR). Relative expression levels of the IL-5R alpha soluble vs. transmembrane isoforms were also analyzed. Stimulation of the non-adherent mononuclear cells with IL-5 resulted in early up-regulation of GATA-1, peaking at 48 h, followed by decreasing expression and down-regulation by 96 h. The CD34+ enriched population demonstrated an equivalent expression pattern (r = 0.963, p = 0.0349). MBP1 mRNA expression [non-adherent mononuclear cells (NAMNCs) and CD34+ alike; r = 0.988, p = 0.012] was slowly up-regulated in response to IL-5, maximal at 96 h. Total IL-5R alpha expression appeared stable over the time-course, mediated by differential expression of the soluble and transmembrane isoforms (i.e., initial increase in the transmembrane contribution followed by a predominance of the soluble isoform by 48-72 h). Multiplex Q-PCR analysis of mRNA from CB demonstrates expression of critical eosinophil-basophil lineage-specific events that are consistent with current understanding of eosinophil differentiation and maturation. The non-adherent mononuclear cell population provides a surrogate signal for the CD34+ progenitor population.

Developmental, Malignancy-Related, and Cross-Species Analysis of Eosinophil, Mast Cell, and Basophil Siglec-8 Expression

“…1). The Siglec-8 mRNA and protein expression occurs in a similar time-frame as the initial expression of mRNA encoding secondary granule proteins such as MBP1 between 3 and 4 days [25] and the first appearance of eosinophilic myelocytes containing fast-green + and eosin + secondary granules on days 6–9 of culture under identical conditions [18]. Also, this time-frame resembles what was reported for the kinetics of Siglec-8 expression in CD34 + -derived human mast cells [15].…”