Jie Mei,1– 3,* Xi-Ya Jiang,1,2,* Bin Zhang,4,* Li Wang,5 Ai-Xi Zhang,6 Jie-Jie Li,1– 3 Shun-Xia Chen,1,2 Xiao Xu,1,2 JingJing Hu,7 Shu-Guang Zhou1– 3 

1Department of Gynecology, The Fifth Affiliated Clinical College of Anhui Medical University, Maternal and Child Health Center of Anhui Medical University, Hefei, Anhui, 230001, People’s Republic of China; 2Department of Gynecology, Anhui Women and Children’s Medical Center, Hefei, Anhui, 230001, People’s Republic of China; 3Department of Gynecology, Linquan Maternity and Child Healthcare Hospital, Fuyang, Anhui, 236400, People’s Republic of China; 4Department of Scientific Research, Hefei Maternity and Child Healthcare Hospital, Hefei, Anhui, 230001, People’s Republic of China; 5Department of Clinical Laboratory, Linquan Maternity and Child Healthcare Hospital, Fuyang, Anhui, 236400, People’s Republic of China; 6Department of Public Health, Linquan Maternity and Child Healthcare Hospital, Fuyang, Anhui, 236400, People’s Republic of China; 7Department of reproduction, The First Affiliated Hospital of Anhui Medical University, Hefei, Anhui, 230032, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Shu-Guang Zhou; JingJing Hu, Email zhoushuguang@ahmu.edu.cn; janejj55@126.com

Background: While endometriosis (EM) has been previously associated with multiple immune factors, the causal relationship underlying these associations remains unclear.
Objective: In this study, Two-sample Mendelian randomization (MR) method was employed to investigate the causal relationship between 731 immune cell traits and EM based on tabulated data from genome-wide association studies (GWAS).
Methods: MR method includes inverse variance weighting (IVW), the weighted median (WM), MR-Egger, the weighted model, and the simple model. IVW is used as the primary method for judging causal effects. Peripheral blood was obtained from EM patients, and the positive immune cell phenotype was confirmed using flow cytometry.
Results: After P-value correction, our two-sample MR showed that CD28 on CD28+ DN (CD4-CD8-) had a suggestive causal relationship with EM (β =0.040, 95% CI =1.02– 1.06, P =0.00029, PFDR = 0.1984). The results of the other two main methods were similar: Weighted median (OR =1.031, 95% CI =1.00– 1.07, P =0.082); MR-Egger (OR =1.032, 95% CI =1.10– 1.06, P =0.044). The flow cytometry results indicated that the expression level of CD28 on CD28+ DN (CD4-CD-8) was significantly increased in the ectopic intima of EM patients.
Conclusion: Our study demonstrated a causal relationship between immune traits and EM, and the results were verified by clinical samples. The study may provide new biomarkers for the early diagnosis and immunotherapy of EM.

Keywords: endometriosis, Mendelian randomization, immune cell traits, flow cytometry