Participation of the novel cytokine interleukin 18 in the host response tointra-amniotic infection

OBJECTIVE: Interleukin 18 is a proinflammatory pleiotropic cytokine that ha s been implicated in the host defense against infection. This study was und ertaken to determine whether interleukin 18 concentrations change in the ma ternal, fetal, and amniotic fluid compartments with labor (term and preterm ) and microbial invasion of the amniotic cavity. STUDY DESIGN: Amniotic fluid was assayed for interleukin 18 in samples obta ined from 285 patients in the following groups: (1) term not in labor (n = 22), in labor (n = 19), and with microbial invasion of the amniotic cavity (n = 16); (2) preterm labor who delivered at term (n = 38), who delivered p reterm but without microbial invasion of the amniotic cavity (n = 41), and preterm labor with microbial invasion of the amniotic cavity (n = 24); (3) preterm premature rupture of membranes without microbial invasion of the am niotic cavity (n = 30) and with microbial invasion of the amniotic cavity ( n = 34); (4) term premature rupture of membranes not in labor (n = 20) and term premature rupture of membranes in labor (n = 19); and (5) midtrimester (n = 22). In addition, cord and maternal plasma samples from women at term not in labor (n = 20) and in labor (n = 20) were assayed for interleukin 1 8. RESULTS: (1) Interleukin 18 was detectable in all amniotic fluid samples an d maternal and umbilical cord blood samples. (2) Interleukin 18 concentrati ons increased with advancing gestational age (r = 0.47; P < .0001). (3) Mic robial invasion of the amniotic cavity in either preterm or term parturitio n was associated with a significant increase in the amniotic fluid concentr ation of interleukin 18 (preterm labor without microbial invasion of the am niotic cavity: median, 14.95 pg/mL; range, 3.9-277.0 pg/mL; vs preterm labo r with microbial invasion of the amniotic cavity: median, 20.75 pg/mL; rang e, 5.53-160.21 pg/mL; P < .02; term labor without microbial invasion of the amniotic cavity: median, 18.73 pg/mL; range, 5.09-95.44 pg/mL; vs term lab or with microbial invasion of the amniotic cavity: median, 24.35 pg/mL; ran ge, 10.07-144.42 pg/mL; P < .004). (4) Both term and preterm parturition we re associated with a modest increase in amniotic fluid interleukin 18 conce ntrations, although this trend did not reach statistical significance. (5) Rupture of membranes at term was associated with a significant decrease in amniotic fluid interleukin 18 concentrations (intact membranes: median, 14. 96 pg/mL; range, <3.89-26.07 pg/mL; vs rupture of membranes: median, 10.1 p g/mL; range, 4.29-21.44 pg/mL; P < .001). CONCLUSION: (1) Interleukin 18 is increased in cases of microbial invasion of the amniotic cavity. (2) Interleukin 18 is detectable in the amniotic, m aternal, and fetal compartments. (3) We propose that this novel cytokine pl ays a role in the host defense against infection.