Pregnancy is associated with a simultaneous but independent increase in circulating CD177pos and immature low-density granulocytes

The neutrophil marker CD177 (NB1, HNA-2a) is expressed by 0-100% of circulating neutrophils in any given donor, dividing neutrophils into 2 distinct subpopulations (CD177pos and CD177neg). High proportions of CD177pos blood neutrophils have been linked to both systemic infections and a range of inflammatory pathologies, but whether this is a cause or a consequence of disease is not known. Many conditions displaying elevated CD177pos neutrophil proportions are also accompanied by the presence of circulating low-density granulocytes. Accordingly, it is tempting to speculate that these 2 events are connected (i.e. that proportions of CD177pos neutrophils increase as a result of an enlarged pool of circulating low-density granulocytes). A temporary increase in CD177pos neutrophils, in combination with the presence of low-density granulocytes, has been reported during pregnancy. The present study aimed to investigate whether elevated proportions of CD177pos neutrophils in peripheral blood from pregnant women can be attributed to the presence of low-density granulocytes. We found that low-density granulocytes were indeed present in pregnancy and included both immature and activated mature neutrophils. The proportion of CD177pos low-density granulocytes increased over time during pregnancy and correlated with a simultaneous increase in immature cells. However, most immature neutrophils were CD177neg, meaning that increased release of immature cells cannot explain the increased proportions of the CD177pos subtype. Therefore, although low-density granulocytes and CD177pos neutrophils are expanded simultaneously during pregnancy, these events occur independently from each other.