Problem The binding of mid-trimester amniotic fluid to cytokines was evaluated.
Method of study Purified tumor necrosis factor-α (TNF-α), interleukin (IL)-10, IL-12, and IL-23 were incubated with amniotic fluid from 25 women undergoing a mid-trimester amniocentesis, or with bovine serum albumin or saline, and cytokine binding to monoclonal antibodies was quantitated by ELISA. Aliquots of amniotic fluid were heated to 95°C for 15 min and then retested for IL-23 binding. The effect of amniotic fluid dilution on IL-23 quantitation was evaluated.
Results All amniotic fluids had a negligible effect on TNF-α, IL-10, and IL-12 detection. In marked contrast, pre-incubation with amniotic fluid from each subject reduced the subsequent ability to detect IL-23 by >50%. The extent of inhibition was directly proportional to the amniotic fluid dilution and was markedly reduced following heating at 95°C for 15 min. Amniotic fluids from White, Black, Asian, East Indian, and Hispanic women were equally effective.
Conclusion Interleukin-23 and IL-12 share a common p40 subunit and no inhibition of IL-12 was apparent. It appeared that a component of mid-trimester amniotic fluid specifically interacts with the p19 subunit unique to IL-23. Mid-trimester amniotic fluid reactivity with IL-23 may be a mechanism to limit intra-amniotic neutrophil-derived inflammation.