Fc receptors are key discriminatory markers of granulocytes subsets in people living with HIV-1

Introduction

Granulocytes are innate immune cells that play a key role in pathogen elimination. Recent studies revealed the diversity of granulocytes in terms of phenotype and function. In particular, a subset of granulocytes identified as low-density granulocytes (LDG) has been described in physiological conditions and with increased frequencies in several pathological contexts. However, the properties of LDG are still controversial as they vary according to the pathophysiological environment. Here we investigated the heterogeneity of granulocyte populations and the potential differences in phenotype and immunomodulatory capacity between LDG and normal density granulocytes (NDG) in people living with HIV-1 (PLWH).

Methods

To this end, we developed an optimized method to purify LDG and NDG from a single blood sample, and performed in-depth, comparative phenotypic characterization of both granulocyte subtypes. We also assessed the impact of purification steps on the expression of cell surface markers on LDG by immunophenotyping them at different stages of isolation.

Results

We identified 9 cell surface markers (CD16, CD32, CD89, CD62L, CD177, CD31, CD10, CXCR4 and CD172α) differentially expressed between LDG and NDG. Noteworthy, markers that distinguish the two subsets include receptors for the Fc part of IgG (CD16, CD32) and IgA (CD89). Importantly, we also highlighted that the purification procedure affects the expression of several cell surface markers (i.e.CD63, CD66b, …) which must be taken into account when characterizing LDG. Our work sheds new light on the properties of LDG in PLWH and provides an extensive characterization of this granulocyte subset in which Fc receptors are key discriminatory markers.

Dysregulated low-density granulocyte contributes to early spontaneous abortion

Spontaneous abortion (SA) is a common adverse pregnancy event with unclarified pathogenesis and limited therapeutic efficiency. Although most SA cases with the euploid embryo(s) are associated with immunological factors, the contribution of low-density granulocyte (LDG) in SA pathogenesis is rarely reported. This study aimed to investigate the serial characteristics and possible contribution of LDG and their subpopulations in early pregnancy, especially in early SA. Unpregnant (UP), normally pregnant (NP), and SA women were recruited, and the peripheral blood and endometrium/decidua were collected for LDG isolation and histological observation. The percentage, phenotype, and subpopulations of LDG were analyzed via flow cytometric analysis, and the ability of Nets formation was assessed by immunofluorescent and immunohistochemical assays. As a result, 43 participants were enrolled, including 10 UP, 15 NP, and 18 SA women. Compared with the UP group, the LDG percentage in peripheral blood mononuclear cells (PBMCs) and decidual immune cells (DICs) increased in the NP group, while the loss of this increase was observed in the SA group. Meanwhile, CD16^int/- cell percentage in peripheral blood LDG (PB-LDG) increased in the NP and SA groups, and insufficient activation of CD16^hi PB-LDG characterized by reduced CD11b expression was discovered in the SA group. Moreover, the LDG percentage in DICs was higher than that in PBMCs, and the decidual LDG (D-LDG) showed a surface marker expression profile that is easier to be activated in the pregnant cohort (NP + SA women). Finally, increased decidual Nets formation was observed in the SA group compared with the NP group, and more Nets formation was detected in D-LDG of NP and SA women following PMA stimulation. Overall, LDG participates in the maintenance of early pregnancy, while dysregulated LDG is responsible for early SA, providing novel potential targets for further exploration of SA pathogenesis and therapeutics.