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Updated: Aug 5, 2026
Collection, Isolation, and Flow Cytometric Analysis of Human Endocervical Samples
Published on: July 6, 2014
Complement protein concentrations and activity in human cervical mucus
J G Marathe1, E Mausser1, J A Politch1
1Department of Medicine, Boston University Aram V. Chobanian & Edward Avedisian School of Medicine, Boston, MA, USA.
Insights
Female reproductive tract immune protection is influenced by complement proteins in cervical mucus. Levels of key complement proteins in cervical mucus vary throughout the menstrual cycle, offering insights into mucosal immunity.
Area of Science:
- Immunology
- Reproductive Biology
- Mucosal Immunology
Background:
- The complement system is crucial for mucosal immunity, but its role in the female reproductive tract (FRT) is poorly understood.
- Hormonal fluctuations during the menstrual cycle may impact complement-mediated protection in the vaginal mucosa.
Purpose of the Study:
- To systematically quantify complement component levels in cervical mucus (CM) and serum (S) across the menstrual cycle.
- To characterize the dynamics of complement in the FRT and its potential hormonal regulation.
Main Methods:
- Ten healthy women provided paired CM and serum samples during follicular, ovulatory, and luteal phases.
- Bead-based multiplex assays were used to quantify 13 primary complement components.
Main Results:
- All 13 complement proteins were detected in CM and S, with C3b/iC3b predominant in CM and C4 in S.
- Complement concentrations were significantly lower in CM than in S, except for C3b/iC3b and C2.
- Levels of C2, C4b, and C5a in CM varied significantly across menstrual cycle phases, while serum levels remained constant.
Conclusions:
- Cervical mucus contains detectable and functional complement proteins.
- Normative values for complement components in CM across the menstrual cycle were established.
- This study provides a foundation for understanding FRT immune mechanisms and hormonal influences on mucosal immunity.
Problem:
Complement, a system of over 30 interacting proteins, functions as a critical immune mediator at mucosal surfaces including the intestine, airway, and nasal mucosae, where it orchestrates complement-dependent cytotoxicity (CDC), complement-dependent phagocytosis (CDP), and inflammatory responses. While complement components have been detected at low levels in genital tract fluids, including cervical mucus, the physiologic dynamics of complement in the female reproductive tract remain poorly characterized. Notably, systematic quantification of complement component levels across the menstrual cycle has not been conducted, limiting our understanding of how hormonal fluctuations may influence complement-mediated protection at the vaginal mucosa.
Method Of Study:
Ten healthy women of reproductive age were recruited to provide paired samples of cervical mucus (CM) and serum (S) during each phase of the menstrual cycle: follicular, ovulatory, and luteal. Samples were analyzed using bead-based multiplex assays to quantify 13 primary complement components.
Results:
All 13 complement proteins tested were detectable in CM and S; C3b/iC3b was the predominant complement component in CM followed by C4 and C3. In contrast, C4 was the dominant component in S followed by C1q and C3. There were significantly higher levels of C2 in CM during the follicular phase of the menstrual cycle vs. the ovulatory phase (1.15±0.80 vs 0.24±0.22μg/mL), C4b (0.56±0.35 vs 0.22±0.36 μg/mL), C5a (1.45±1.09 vs 0.38±0.48 μg/mL) In contrast, no differences were found in serum complement levels were during the menstrual cycle. Complement concentrations were on average 308-fold (median= 84) lower in CM than in S, except for C3b/iC3b which was only 5 to 7.5-fold lower in CM, and C2 which was higher in CM at the luteal and follicular phases. Midcycle cervical mucus was capable of inducing complement-mediated hemolysis at about 1/3 the potency of serum.
Conclusion:
Cervical mucus contains detectable and functional levels of complement proteins. These normative values can provide a foundation for future studies on immune mechanisms in the FRT.
