Sex differences in preterm cytokine and inflammasome responses and modulation by exogenous sex steroids.

Background: Preterm infants are at increased risk of sepsis compared to adults and older children. Preterm immune cells have altered cytokine responses compared to term neonates and adults and all have sex-related differences in immunity. We examined inflammasome activation and cytokines with endotoxin and sex steroid hormones between preterm and term neonates.

Methods: Preterm (n = 40) and term (n = 32) peripheral blood samples were incubated with Lipopolysaccharide (LPS), Estradiol (E2), Progesterone (Pg) or Pam3CSK4 and biomarkers were analysed by ELISA. Inflammasome genes, NLR family pyrin domain containing 3 (NLRP3), apoptosis-associated speck-like protein (ASC), Interleukin-1 beta (IL1-β) and Absent In Melanoma 2 (AIM 2) were analysed with Taqman RT-PCR.

Results: IL-1β cytokine expression was reduced by female sex hormones and notably the effect of estradiol was greatest in the preterm population. Female preterm neonates were more responsive to the anti-inflammatory effect of progesterone than male preterm infants. Term neonates had higher IL-1β, IL-18 and IL-1RA expression than preterm infants. Overall, in preterms, E2 and Pg lowered cytokine expression levels. Inflammasome gene expression profiles did not differ between preterm male and female neonates.

Conclusion: Sex hormones altered the expression of multiple cytokines, and cytokine responses differ by sex. Gestation plays an important role in the inflammatory response, and we note term infants have a more robust profile while preterm infants are more responsive to hormonal stimulus. Female sex hormones have an important role in modulating neonatal immune response and may contribute to the female immune advantage.

Impact: Female sex hormones play an important role in modulating the neonatal immune response. This is reflected clinically by better bacterial clearance and improved sepsis outcome in females. This study aims to test the hypothesis that male and female neonates differ in their cytokine and inflammasome response and in response to endotoxin and sex steroid hormones. In preterm infants there is a sex difference in IL-1b responses which is observed rapidly following endotoxin stimulation. Differing immune responses according to sex has implications for future clinical application. Further work to characterise these sex differences may help in guiding therapy during sepsis.