Premature birth is the leading cause of perinatal mortality and morbidity worldwide. The Perinatology Research Branch has defined preterm labor as a syndrome and determined that at least 25 percent of all preterm infants are born to women with subclinical intrauterine infection. Moreover, the branch has provided evidence that a substantial number of premature neonates are critically ill before birth and has proposed that the onset of premature labor has survival value in the context of intrauterine infection. This year, the branch studied the frequency of intravascular inflammation in normal pregnancy, preterm labor, pyelonephritis during pregnancy, and the diagnostic and prognostic value of matrix metalloproteinase-8 determinations in the evaluation of patients with preterm labor and preterm premature rupture of membranes.

Phenotypic and Metabolic Characteristics of Monocytes and Granulocytes in Normal Pregnancy and Maternal Infection
Chaiworapongsa, Romero
A traditional paradigm in reproductive immunology is that the fetus is a semiallograft (thus, somewhat comparable to a transplanted organ) and that the maintenance of pregnancy requires either evasion of immune surveillance or suppression of the maternal adaptive immune response. Yet, despite intensive investigation, evidence of substantial and generalized immunosuppression during normal pregnancy has not been conclusive. Recent studies indicate that normal pregnancy produces changes in peripheral blood leukocytes akin to those of sepsis, observations that have implications for understanding the susceptibility of pregnant women to sepsis, the pathophysiology of preeclampsia, and the biology of normal pregnancy. The branch has undertaken a series of studies to determine the state of neutrophil and monocyte activation during pregnancy. Using flow cytometry, we were able to determine that normal pregnancy is characterized by phenotypic and metabolic changes in monocytes and granulocytes consistent with intravascular inflammation. The physiologic activation of the innate limb of the immune response could be a compensatory mechanism to maintain host defense when the adaptive component of the immune system is suppressed. Moreover, patients with pyelonephritis were found to have more marked phenotypic and metabolic changes of leukocytes than normal pregnant women, indicating that the innate limb of the immune response is not maximally activated during normal pregnancy.

Some pregnant women develop a systemic inflammatory response syndrome or overwhelming sepsis with infections that, clinically, do not appear to be severe enough to explain the development of multiple organ failure. Indeed, it is known that pregnant women are more susceptible to the effects of microbial products. For example, pregnant women with pyelonephritis are at risk for developing adult respiratory distress syndrome, a complication that is rare in the nonpregnant state. Moreover, pregnant animals develop the Shwartzman reaction after a single injection of endotoxin while nonpregnant animals require a priming dose. This susceptibility to microbial products may be a consequence of the physiologic activation of the innate component of the immune response. Further studies are required to determine if host hyperresponsiveness or hyporesponsiveness may result in a systemic inflammatory response syndrome or overwhelming sepsis, respectively. Why some pregnant women are more susceptible to the effects of microbial products than others is unknown. Recent observations implicate polymorphisms in the genes that encode for some cytokines (i.e., tumor necrosis factor allele 2) involved in the control of the inflammatory response, susceptibility to septic shock, and death in nonpregnant subjects. It is possible that these factors may also be important during pregnancy when the host is primed and exposed to the risk of infection.

Maternal Intravascular Inflammation in Premature Labor
Chaiworapongsa, Romero
Experimental and clinical studies support a role for the fetus in the control of the onset of labor. Fetal systemic inflammation, but not a maternal inflammatory response, has been linked to the onset of preterm labor and delivery on the basis of the determination of inflammatory cytokines in fetal and maternal blood. Parturition, however, requires recruitment and participation of several local maternal structures such as the myometrium, cervix, and decidua as well as the involvement of the maternal neuroendocrine system. Moreover, recent experimental evidence indicates that a systemic response is required for the onset of parturition in the context of infection in pregnant animals. A prospective cross-sectional study performed by the branch demonstrated that premature labor is associated with phenotypic and metabolic changes in neutrophils and monocytes consistent with intravascular inflammation. These changes were observed even in the absence of demonstrable infection, and we interpret the findings as consistent with the participation of the innate component of the maternal immune response in the process of preterm parturition.

Intravascular Inflammation in Preeclampsia
Chaiworapongsa, Romero
Preeclampsia, a syndrome characterized by hypertension and proteinuria during pregnancy, is a leading cause of maternal death and perinatal morbidity and mortality worldwide. Systemic maternal inflammation has been proposed as the cause of the maternal syndrome of preeclampsia. Placental products (of particulate or soluble nature) have been implicated in the activation of leukocytes in this disorder. However, there is controversy as to whether the clinical manifestations of preeclampsia are due to systemic maternal inflammation and even whether neutrophil activation accompanies the disease. Our laboratory conducted a prospective cross-sectional study indicating that neutrophils and monocytes of preeclamptic women have phenotypic and metabolic changes consistent with intravascular inflammation. Future studies are planned to determine whether intravascular inflammation precedes the clinical development of the disease and the mechanisms responsible for the metabolic and phenotypic changes observed in neutrophils.

The Clinical Value of Matrix Metalloproteinase-8 Determinations in Patients with Preterm Labor and Preterm Premature Rupture of Membranes
Romero, Chaiworapongsa, Conoscenti, Edwin, Kim
Intra-amniotic infection is frequently present in patients with preterm labor and intact membranes as well as in patients with preterm premature rupture of membranes. Intrauterine infection is a risk factor for preterm delivery, clinical chorioamnionitis, spontaneous rupture of membranes, and adverse perinatal outcome. The gold standard for the diagnosis of intra-amniotic infection is the isolation of microorganisms from the amniotic fluid. However, results may take several days and therefore may not be available in time for management decisions. Normal amniotic fluid does not contain white blood cells. The cell type most frequently recruited into the amniotic cavity during the course of an inflammatory process is the neutrophil. Amniotic fluid neutrophils are thought to be of fetal rather than of maternal origin; therefore, their presence in amniotic fluid is likely to reflect a fetal inflammatory response. Matrix metalloproteinases (MMPs) are a family of endogenous enzymes with potent matrix degrading capabilities. These enzymes have been implicated in the process of parturition, rupture of membranes, and intra-amniotic infection. MMP-8 (collagenase 2), or human neutrophil collagenase, is contained in the specific granules of polymorphonuclear leukocytes and is released on chemotactic stimulation in vitro or during inflammatory conditions in vivo. Studies conducted by the branch have indicated that MMP-8 concentrations are elevated in the amniotic fluid of patients with intra-amniotic infection, preterm labor, and preterm premature rupture of membranes. This past year, the branch conducted two studies that provide evidence that MMP-8 concentrations in the amniotic fluid have diagnostic and prognostic value. In patients with preterm labor and intact membranes, an elevated amniotic fluid MMP-8 concentration identified patients at risk for impending preterm delivery and adverse neonatal outcome. In patients with preterm premature rupture of membranes, MMP-8 concentrations were a strong predictor of the duration of pregnancy and adverse neonatal outcome. Moreover, MMP-8 was a better predictor of intra-amniotic infection than either IL-6 or amniotic white blood cell count.