Background: Secretory immunoglobulin A (SIgA) is the most abundant antimicrobial protein in saliva, with reductions linked to an increased risk of respiratory infection. Male-female differences in mucosal immunity are reported, but findings are contradictory, which may be explained by a lack of control over menstrual phase. Pregnant women, who have high circulating concentrations of oestrogen and progesterone, have higher saliva SIgA than non-pregnant women, providing preliminary evidence that female sex hormones modulate mucosal immunity. However, little is known about how oral mucosal immunity varies across the menstrual cycle.
Aim: To examine oral mucosal immunity across the menstrual cycle.
Methods: Twenty-six healthy naturally menstruating women with confirmed ovulatory menstrual cycles (age: 27 ± 5 years, BMI: 24 ± 5 kg/m2) visited the laboratory in their early follicular (EF; days 1-5 of their cycle) and mid-luteal phases (ML; days 5-10 post-ovulation). Participants had not used hormonal contraceptives in the last six months. Ovulation was confirmed using urine analysis for luteinising hormone. Participants arrived at the laboratory following an overnight fast, having avoided strenuous exercise, alcohol and over-the-counter medication for 24 hours before, and had not self-reported illness or infection in the prior seven days. Participants provided unstimulated saliva samples, which were analysed using ELISA for SIgA. Saliva collection was timed, and volume determined by weighing pre and post to calculate flow rate and secretion rate.
Results: Participants had higher saliva SIgA secretion rate during the ML than EF phase (57 ± 40 vs 46 ± 39 μg/min, respectively; P=0.04). There were no differences in saliva flow rate or SIgA concentration between phases.
Conclusion: Resting oral mucosal immunity varied across the menstrual cycle in naturally menstruating women. Women may be more susceptible to respiratory infection in the early follicular than luteal phase. Researchers should account for menstrual cycle phase when measuring mucosal immunity.