Human beta-defensin-2: a natural antimicrobial peptide present in amniotic fluid participates in the host response to microbial invasion of the amniotic cavity

Abstract

Objective: Human beta-defensin-2 (HBD-2) is a potent antimicrobial peptide that is part of the innate immune response. The purpose of this study was to determine whether HBD-2 is present in amniotic fluid and if its concentration changes with microbial invasion of the amniotic cavity (MIAC) and labor.

Study design: Amniotic fluid was retrieved by amniocentesis from 318 patients in the following groups: (1) mid-trimester (n=75); (2) term not in labor (n=28) and in labor (n=51); (3) preterm labor and intact membranes without MIAC who delivered at term (n=36), who delivered preterm without MIAC (n=52), and preterm labor with MIAC who delivered preterm (n=25); and (4) preterm premature rupture of membranes (preterm PROM) with (n=25) and without MIAC (n=26). MIAC was defined as a positive amniotic fluid culture for microorganisms. Amniotic fluid HBD-2 concentrations were determined using a sensitive and specific ELISA. Non-parametric statistics were used for analysis.

Results: (1) HBD-2 was detected in all amniotic fluid samples; (2) the concentration of HBD-2 did not change with gestational age from mid-trimester to term (p=0.8); (3) intra-amniotic infection was associated with a significant increase in amniotic fluid concentrations of HBD-2 in both women with preterm labor and intact membranes, and women with preterm PROM (p<0.05 for each comparison); (4) patients with preterm labor and a negative amniotic fluid culture who delivered preterm had a higher median amniotic fluid HBD-2 concentration than those with preterm labor who delivered at term (p=0.001); and (5) among patients with preterm labor without MIAC, those who had intra-amniotic inflammation (amniotic fluid white blood cell count>100 cells per mL) had a higher median amniotic fluid concentration of HBD-2 than those without this condition (p<0.002).

Conclusion: (1) Amniotic fluid contains HBD-2, a natural antimicrobial peptide, and this may account for some of the antimicrobial activity of amniotic fluid; (2) amniotic fluid HBD-2 concentrations are increased in women with MIAC, regardless of the membrane status (intact membranes or PROM); and (3) we propose that amniotic fluid HBD-2 is part of the innate immune system within the amniotic cavity.

Figure 1

Amniotic fluid (AF) concentration of HBD-2 in women in the mid-trimester who delivered a normal neonate at term and in women at term without labor. There was no difference between the median AF concentration of HBD-2 in women in the mid-trimester and those at term without labor [median 3 ng/ml (range 0.3–11.8) vs. median 2.9 ng/ml (range 0.3–15.1), respectively; p=0.8].

Figure 2

Amniotic fluid (AF) concentration of HBD-2 in women with preterm labor and intact membranes. The median AF concentration of HBD-2 was significantly higher in women with preterm labor who delivered preterm than in those who delivered at term [median 5.5 ng/ml, (range 0.1–140.2) vs. median 3.4 ng/ml, (range 0.5–17), respectively; p=0.001]. Similarly, the median AF concentration of HBD-2 in women with microbial invasion of the amniotic cavity (MIAC) was significantly higher than in women with preterm labor without MIAC who delivered preterm [median 17.6 ng/ml, (range 0.9–105.2) vs. median 5.5 ng/ml, (range 0.1–140.2), respectively; p=0.001]. The median AF concentration of HBD-2 was significantly higher in women with MIAC than in those with preterm labor who delivered at term [median 17.6 ng/ml, (range 0.9–105.2) vs. median 3.4 ng/ml, (range 0.5–17), respectively; p=0.004].

Figure 3

Amniotic fluid (AF) concentration of HBD-2 in women with preterm premature rupture of membranes (PROM) with and without microbial invasion of the amniotic cavity (MIAC). The median AF concentration of HBD-2 was significantly higher in women with preterm PROM and MIAC than in those with preterm PROM without MIAC [median 5.8 ng/mL (range 0.5–66.7) vs. median 3.4 ng/mL (range 1–19.6), respectively; p=0.02].

Figure 4

Amniotic fluid (AF) concentration of HBD-2 of normal pregnant women at term. There was no difference in the median AF HBD-2 concentration between women at term not in labor and those in labor [median: 2.9 ng/mL (range 0.3–15.1) vs. median: 4.3 ng/mL (range 0.3–48.9), respectively; p=0.4].