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Systemic complement C3 reduction in infertile women with endometrial dysbiosis: preliminary observations
Shinya Yamaguchi1, Takumi Sato2, Hirotaka Matsumi3,4
1Faculty of Medicine, The University of Tokyo, Tokyo, Japan.
Context:
Endometrial dysbiosis has been linked to infertility, but its relationship with systemic immune activity remains unclear.
Aims:
To examine whether endometrial microbiota phenotype is associated with serum complement profiles in infertile women.
Methods:
We enrolled 105 infertile women and classified endometrial microbiota by 16S rRNA gene sequencing as Lactobacillus-dominant microbiota (LDM) or non-LDM (NLDM). Complement data were available in 27 women: after excluding cases with missing C-reactive protein (CRP; n = 2) or CRP above the 95th percentile (n = 2), 23 women were analyzed for C3/C4 and 19 for CH50. Group comparisons used Welch's t-test and Fisher's exact test.
Key Results:
NLDM was associated with lower serum C3 than LDM (101.5 ± 12.4 vs 121.0 ± 18.0 mg/dL; P = 0.006). C4 and CH50 did not differ significantly between groups.
Conclusions:
Endometrial dysbiosis was associated with selective C3 reduction in this infertile cohort, consistent with mild complement consumption.
Implications:
Serum C3, interpreted with microbiota profiling, may provide a practical adjunct marker of inflammation-related infertility in routine care. Larger prospective studies are needed to validate these preliminary findings.
