O-030 Disturbed homeostasis of regulatory T-cells and imbalanced signal transducer and activator of transcription 5 (STAT5) in women with ovarian endometriosis
Authors: Knez J , Al Mahdawi L , Kovačič B , But I , Rakic K , Reljič M , Goropevšek A 
Published: June 2022

Abstract

Study question
Do women with endometriosis have altered cytokine signalling and regulatory T-cell (Treg) homeostasis compared to controls?

Summary answer
Altered homeostasis of circulating Treg cells seems to be associated with STAT5 phosphorylation, which is significantly increased in women with ovarian endometriosis compared to controls.

What is known already
Cytokine signaling influences homeostasis of regulatory T-cells (Treg), which play a crucial role in cell-mediated immunity and are responsible for certain immune disorders. Endometriosis is a condition associated with altered immune response to endometrial cells. While some animal studies have shown that Treg deficiency facilitates ectopic implantation of endometriosis, a recent study performed in a small number of women with endometriosis has shown the decreased proportion of a specific-activated subset of Treg cells in the endometrioma compared to controls. There is no data characterising cytokine signalling in circulating Treg subsets, which could underlie their altered homeostasis in women with endometriosis.

Study design, size, duration
A prospective cohort study including 14 women with endometriosis and 10 controls at a university-based tertiary care centre for endometriosis. The data were collected from August 2020 to September 2021. Serum blood samples were collected in the early follicular phase of the menstrual cycle, in women not using any hormonal treatment. Early follicular steroid hormone levels were measured. A detailed expert ultrasound examination was performed to diagnose and accurately map endometriotic lesions.

Participants/materials, setting, methods
We investigated signal transducer and activator of transcription (STAT) signalling in peripheral blood Treg subsets, including CD45RA+FOXP3low+ naive Tregs (nTregs). Expression of proliferation marker Ki-67 and STAT activation also in FOXP3- conventional (Tcon) CD4+T-cells was monitored, hypothesising that defects in this pathway could be associated with altered Treg/Tcon homeostasis in endometriosis. Immunophenotyping and flow cytometry methods with phospho-specific antibodies that allow analysis of basal STAT activation/phosphorylation also in rare subsets of Treg cells were used.

Main results and the role of chance
Among women with endometriosis, 5 had evidence of ovarian and deep infiltrating endometriosis (DIE), 5 had only ovarian endometriosis and 4 had only evidence of DIE. Groups were comparable in their clinical characteristics, there was no difference in the median age of women with endometriosis and controls; 31 (range 23-45) vs. 34 (range 27-39).
We demonstrated significantly higher levels of phosphorylated STAT5 (pSTAT5) in nTreg from women with ovarian endometriosis compared to controls (p = 0.026). To assess the homeostatic balance between the nTreg and Tcon, we compared pSTAT5 levels between these cell subsets in each patient. STAT5 phosphorylation was significantly higher in Tcon than in nTreg subset (p &lt; 0.001).
Considering STAT5 activation in nTreg subset, this was positively correlated with the proportion of nTreg among CD4+T-cells (rs=0.54, p = 0.027) in all women with endometriosis. We also found a significant positive correlation between pSTAT5 levels in Tcon from women with endometriosis and the percentage of Ki-67+ cells in the Tcon subset (rs=0.66, p = 0.005) as well a significant correlation between luteinizing hormone (LH) levels and pSTAT5 in Tcon subset of CD4 cells (rs=0.71, p = 0.02). This implies LH-dependent imbalanced STAT5 signalling that could be responsible for increased Tcon homeostatic proliferation.

Limitations, reasons for caution
Our sample size is relatively small and the findings should be validated in future prospective studies. Due to the sample size, there is a risk for Type I error, although the results are coherent in indicating disturbance of Treg homeostasis.

Wider implications of the findings
Our study suggests that altered STAT5 signalisation may be associated with disturbed nTreg/Tcon homeostasis, which seems to be mostly prominent in women with ovarian endometriosis. If confirmed by further studies in the future, targeted treatment options could be developed to supress progress of endometriosis in this group of women.

Trial registration number
not applicable