P–238 Impaired oocyte fertilization is associated with a proinflammatory M1 phenotype of macrophages and the activation of the NLRC4 inflammasome
Authors: Rösing B , Bielfeld A , Neulen J , Habib P 
Published: August 2021

Abstract

Study question
Are inflammatory signatures in the blood of clinically asymptomatic patients predictive for oocyte fertilization success in ART treatment?

Summary answer
The proinflammatory M1 phenotype of macrophages combined with increasing numbers of cytotoxic T-cells and an upregulated inflammasome NLRC4 is associated with impaired oocyte fertilization.

What is known already
Oocyte fertilization is an indispensable step towards embryogenesis and reproductive success. Patients with acute or chronic inflammation are at risk of reduced fertilization rates and failure of assisted reproductive technology (ART) treatment. Inflammasomes are intracellular multiprotein complexes that mediate inflammatory tissue remodeling. They can be activated by endogenous and exogenous stimuli and result in maturation of the cytokines IL–1βand IL–18. Appropriate inflammasome activation serves for pathogen defense and tissue damage repair, while aberrant activation of inflammasomes can enhance uncontrolled tissue damage.

Study design, size, duration
This a prospective study including 39 patients stratified by fertilization rate (cut off 66%) of mature M II oocytes after ICSI procedure, compares 20 patients with high (mean 84,8%, range 67 –100%) versus 19 patients with low (mean 29.4%, range 0–65%) rates.

Participants/materials, setting, methods
We performed FACS analysis of immune cell composition (leukocytes, neutrophils, monocytes, macrophage types M1 and M2, cytotoxic T-cells, T-helper cells) and utilized RT-qPCR analysis of three inflammasomes (AIM 2, NLRP3 and NLRC4) and their down-streaming proteins caspase 1 and IL–1ß. We focused on an initial and a late state during controlled ovarian stimulation (COS) procedure.

Main results and the role of chance
This study reports a cellular and molecular inflammatory signature associated with reduced oocyte fertilization rates after ICSI treatment in clinically asymptomatic patients.
On a cellular level proinflammatory M1 macrophages were significantly elevated in the low fertilization group (p &lt; 0.01), additionally the ratio of proinflammatory M1 macrophages to anti-inflammatory M2 phenotype was inversely associated with oocyte fertilization rate (p &lt; 0.001). Cytotoxic T cells (p &lt; 0.05) and the inflammasome NLRC4 (p &lt; 0.01) revealed identical patterns of association with fertilization rates in the group comparison.
In line with this pattern, there was a significant upregulation of Caspase 1 with a consecutive increase in IL–1ß activity in women with low fertilization rates (p &lt; 0.05).
No significant association was shown for the other tested immune cells (leukocytes, neutrophils, monocytes, T-helper cells) and inflammasomes (NLRC3, AIM2).

Limitations, reasons for caution
The preliminary results in this small study indicate an activation of the inflammasome NLRC4. This, however, has to be assessed on the protein level in a larger group of patients.
Wider implications of the findings: Systemic macrophage augmentation of M1 phenotype and cytotoxic T cell presence in combination with upregulated inflammasome NLRC4 are associated with impaired oocyte fertilization. The predictive information of the identified immunologic signature could indicate targeted treatment to down regulate systemic inflammation and the use of oocyte activators in the ART laboratory.

Trial registration number
none