Characterization of neutrophil subsets in healthy human pregnancies

Abstract

We have previously shown that in successful pregnancies increased arginase activity is a mechanism that contributes to the suppression of the maternal immune system. We identified the main type of arginase-expressing cells as a population of activated low-density granulocytes (LDGs) in peripheral blood mononuclear cells and in term placentae. In the present study, we analyzed the phenotype of LDGs and compared it to the phenotype of normal density granulocytes (NDGs) in maternal peripheral blood, placental biopsies and cord blood. Our data reveal that only LDGs but no NDGs could be detected in placental biopsies. Phenotypically, NDGs and LDGs from both maternal and cord blood expressed different levels of maturation, activation and degranulation markers. NDGs from the maternal and cord blood were phenotypically similar, while maternal, cord and placental LDGs showed different expression levels of CD66b. LDGs present in cord blood expressed higher levels of arginase compared to maternal and placental LDGs. In summary, our results show that in maternal and cord blood, two phenotypically different populations of neutrophils can be identified, whereas in term placentae, only activated neutrophils are present.

Figure 1. Phenotypic analysis of LDGs and NDGs.

LDGs and NDGs were isolated as described in materials and methods (n = 7) and the expression levels of arginase, CD66b, CD15, CD63, CD33 and CD16 were determined by flow cytometry. Statistical significance was determined by a two-tailed Mann-Whitney test. Box = interquartile range and median; whiskers = range.

Figure 2. Comparison of the phenotype of LDGs in neonate and maternal blood and placentae.

LDGs were isolated as described in materials and methods (n = 7) and the expression levels of CD66b was determined by flow cytometry. Statistical significance was determined by a kruskal-Wallis test. Box = interquartile range and median; whiskers = range.

Figure 3. Percentage of LDGs in neonatal and maternal blood and placentae.

LDGs were isolated as described in materials and methods (n = 7) and the percentage of CD15⁺ arginase⁺ cells was determined by flow cytometry. The percentage of LDGs present in the peripheral blood of healthy controls was 0.24±0.3 Statistical significance was determined by a kruskal-Wallis test. Box = interquartile range and median; whiskers = range.