Preeclampsia and coronary heart disease share many common pathophysiologic features and risk factors. One common feature is endothelial dysfunction, which may derive from inflammation. In atherosclerosis, injury-induced mononuclear cell accumulation, migration and proliferation of smooth muscles, and formation of fibrous tissue ultimately lead to plaque formation and vessel obstruction.1 These pathologic features, plus the finding that an elevation of inflammatory markers precedes atherosclerosis,2 have suggested an inflammatory origin to the altered endothelial dysfunction seen in atherosclerosis. In preeclampsia, too, heightened intra-vascular inflammation has been suggested as the origin of the abnormal endothelial function.3,4
Accumulating evidence suggests that infection by Chlamydia pneumoniae, a common pathogen causing upper and lower respiratory tract disease, may be involved in the endothelial injury that marks atherosclerosis. Chlamydia pneumoniae is prevalent in atherosclerotic lesions but generally absent in normal coronary arteries.5 It induces atherosclerotic lesions in mice and rabbits,6–8 particularly in association with hypercholesterolemia. Further, in some studies, but not all, C pneumoniae antibodies are more common in individuals with myocardial infarction and coronary heart disease death.9–18 Finally, recent studies among patients with coronary artery syndromes have shown that, shortly after their initiation, macrolides reduce the risk of subsequent adverse cardiac events.16–18
In this study we explored the relationship between C pneumoniae seroprevalence and preeclampsia. We assessed the occurrence of immunoglobulin (Ig) G, IgM, and IgA antibodies to C pneumoniae and IgG antibodies to Chlamydia trachomatis and Chlamydia psittaci among women with preeclampsia and pregnant controls.
MATERIALS AND METHODS
Serum samples were obtained as part of an ongoing study of preeclampsia that has been approved by the Magee-Womens Hospital Institutional Review Board.19 Samples were obtained at the time of admission for labor and delivery, processed within 2 hours, and stored at −70C. Samples were randomly selected from 37 nulliparous pregnant women with preeclampsia and from 37 nulliparous pregnant women with uncomplicated, term pregnancies.
Preeclampsia was defined using the criteria of hypertension, proteinuria, hyperuricemia, and resolution of hypertension and proteinuria after pregnancy. Hypertension was defined as an increase of 30 mm Hg systolic or 15 mm Hg diastolic blood pressure as compared with values obtained before 20 weeks' gestation, or an absolute blood pressure of 140/90 mm Hg or higher after 20 weeks' gestation if earlier blood pressure values were unknown.20 Among the 27 preeclamptic patients, all had a blood pressure value greater than 140 mm Hg systolic or 90 mm Hg diastolic. Proteinuria was defined as 300 mg per 24-hour collection, or more than 2+ on a voided or 1+ on a catheterized random urine specimen. Hyperuricemia was defined as more than one standard deviation above the usual for the gestational age at which the sample was obtained (5.5 mmol/L at term). All abnormalities had to return to normal by 12 weeks postpartum for the patient to be considered preeclamptic.
Sera from preeclamptic and control women were sent in batches to MRL Reference Laboratory (Cypress, CA) for the detection of antibodies to C pneumoniae using an established microimmunofluorescence technique for detection of antibodies.21 Briefly, antigen was fixed to a slide and probed with patient sera. Antibody specific to IgG, IgM, and IgA was fluoroscein labeled and used as a secondary probe. Positive samples were diluted to determine the absolute antibody titer. To rule out the presence of cross-reactive antibody, testing was also performed for C trachomatis and C psittaci. For all organisms a titer of at least 1:16 was considered positive for IgG and IgA, where as a titer of at least 1:10 was considered positive for IgM.
Covariate information was obtained by review of the maternal and neonatal medical records at the time of labor and delivery. Information was obtained on maternal age, race (white versus nonwhite), current smoking, gestational age at delivery, and infant birth weight.
We evaluated data on demographic and clinical features and serologies among the 37 preeclamptic women and 37 controls. Sample size analyses suggested that with 17–45 cases and the same number of controls we could detect a difference between a prevalence of 10–20% in controls and 50–60% in cases, the magnitude of difference initially observed for seroprevalence of C pneumoniae among subjects with and without coronary artery disease.9 This calculation and logistical considerations led us to our sample size.
Odds ratios were the main measure used for comparison of preeclamptic patients and controls. Cross-sectional differences in covariates were analyzed. The proportions of women with a positive serum test at a titer of at least 1:16 (for IgG and IgA) and at least 1:10 (for IgM) were then compared, first using the Fisher exact test and then odds ratios. Subsequently, a series of interval antibody titers to C pneumoniae were used to compare the seroprevalence rates between cases and controls, using odds ratios as the measure of comparison. Logistic regression analyses were used to adjust for age and then for gestational age, considering preeclamptic versus control status as the main dependent variable and antibody presence as the main independent variable.
The 37 women with pregnancies complicated by preeclampsia were not significantly different from the 37 with unaffected term pregnancies with respect to age, race, or smoking status (Table 1). As expected, women with preeclampsia were significantly more likely to deliver preterm.
The seroprevalence of IgG to C pneumoniae at a titer of at least 1:16 was more common in women with preeclampsia (25 of 37) than in controls (15 of 37) at a significance level of P < .05 (Figure 1). Positive titers for C pneumoniae IgM and IgA were not significantly more likely among preeclamptic women. Women with preeclampsia, as compared with controls, also had no greater seroprevalence of IgG to C trachomatis or C psittaci (Figure 2).
We further explored the possibility that higher titers of IgG antibodies to C pneumoniae might reflect higher risk (Table 1). At a cutoff of 1:16, the risk of seropositivity to C pneumoniae was 3.1 (95% confidence interval 1.2, 7.9). Odds ratios for antibody titers of 1:16 or 1:32, 1:64, and at least 1:128 were 4.6, 3.1, and 2.6, respectively, indicating a lack of higher risk with higher titers. Given the smaller sample sizes involved in these subset analyses, none of the associations between specific antibody titer cutoffs and preeclampsia were significant. Age adjustment did not substantially alter these results (data not shown). Gestational age adjustment also had little impact on the odds ratios but widened the confidence intervals because gestational age data were missing for a third of study women.
We found that IgG seroprevalence to C pneumoniae was more common among women with preeclampsia than among women with unaffected term pregnancies. The fact that we did not find an association to preeclampsia for IgG seroprevalence to C trachomatis or C psittaci suggests a specific association between preeclampsia and the particular species of Chlamydia that has been associated with atherosclerosis. This finding is consistent with the known lack of cross-reactivity of the immunofluorescent assay used.21 Altogether, it is unlikely that cross-reactivity to other pathogens might explain the relationship found between preeclampsia and C pneumoniae.22
An association to preeclampsia was not found for IgA or IgM seroprevalence to C pneumoniae. Neither did we find a dose-response relationship between IgG titer and risk of preeclampsia. Both of these findings suggest that it is past, persistent, or chronic active infection and not acute infection or reinfection with C pneumoniae that is associated with preeclampsia. Acute infection or reinfection would cause an elevation in IgM titers. Further, studies of paired sera obtained from patients with pneumonia indicate that acute infection generally causes high titers (1:512 or 1:1024).21 In animal models, the induction of atherosclerosis has required persistent or chronic active infection, rather than a single past exposure to C pneumoniae. Repeated respiratory infection with C pneumoniae, and not a single, acute infection, is needed to promote the growth of atherosclerotic plaque in rabbits. Antibiotic treatment can prevent or reduce atherosclerotic changes in animals being reinfected with C pneumoniae.23 Human serological data suggest that recent reinfection also may be important, at least in relation to myocardial infarction or coronary heart disease death. Although prospective observational studies are more mixed than case-control studies24 in showing an association between C pneumoniae and coronary heart disease,10–15 two prospective observational studies that did show an association related recent antibody positivity and high titers of C pneumoniae to newly manifest coronary heart disease.12,14 There is some, limited evidence that antibiotic use in pregnancy may reduce the risk of preeclampsia.25
How might C pneumoniae increase the risk of preeclampsia? Preeclampsia can be considered a two-stage disorder, with the first stage involving abnormal placental implantation and the second being the abnormal maternal adaptation to the pregnancy that results in systemic dysfunction.26 In healthy pregnancies, the maternal spiral arteries undergo extensive remodeling.27 This remodeling is incomplete in preeclampsia. Reduced placental perfusion, the outcome of abnormal spiral artery remodeling, is considered to be the root cause of preeclampsia. Further, in preeclamptic spiral arteries a frequent histological finding thought to contribute to reduced placental perfusion is atherosis, a pathologic lesion involving the same lipid-laden foam cells observed in atherosclerosis. Chlamydia pneumoniae may contribute to atherosclerosis by bringing monocytes to areas of arterial damage to form foam cells, leading to plaque, and thrombosis.28 Similarly, past, persistent, or recurrent infection with C pneumoniae may contribute to abnormal vascular function, atherosis, and the abnormal placental perfusion that marks the first stage of preeclampsia.
Chlamydia pneumoniae may also contribute to the second stage of preeclampsia through endothelial dysfunction.4 Overweight, diabetes, hyperlipidemia, and hypertension are all established risk factors for coronary heart disease and, when present in women entering pregnancy, greatly enhance their likelihood of developing preeclampsia.29 The pathophysiology shared by all of these risk factors is endothelial dysfunction. Inflammation also increases endothelial dysfunction by enhancing oxidative stress.30 Markers of inflammation independently predict incident coronary artery disease, and a predisposition to a muted inflammatory response reduces the risk of coronary artery disease.2,31 Such direct temporal relationships have yet to be demonstrated for preeclampsia, but inflammatory mediators are elevated in it.3Chlamydia pneumoniae may, in both coronary heart disease and preeclampsia, be an initiator of the inflammatory process. Alternatively, C pneumoniae may simply reside on monocytes activated during inflammation.24 If so, the association between C pneumoniae and coronary heart disease or preeclampsia may be an effect rather than a cause.
We recognize that weaknesses of our study were its small size and cross-sectional design. Further, although race did not significantly differ between cases and controls, nonwhite race was more common in patients and may have confounded our results. Our study also had strengths. Because our case and control selection was embedded in a large study of preeclampsia, we were able to approach a large proportion of eligible women. Thus, selection of cases and controls was relatively unbiased. That the prevalence of C pneumoniae in this study is similar to that seen in young adults in Europe reassures us as to the generalizability of our finding.32 Further, we used a rigorous case definition for preeclampsia and well-established methods for the serological detection of C pneumoniae. However, based on this single report in a modest-sized sample, it would be premature to consider our observed link between C pneumoniae and preeclampsia to be other than an association in need of replication.
1. Lie JT. Atherosclerosis—pathology of coronary artery disease. In: Giuliani ER, Fuster V, Gersh BJ, McGoon MD, McGoon DC, eds. Cardiology: Fundamentals and practice. St. Louis: Mosby Year Book, 1987:1211–31.
2. Ridker PM, Hennekens CH, Buring JE, Rifai N. C reactive protein and other markers of inflammation in the prediction of cardiovascular disease in women. N Engl J Med 2000;342:836–43.
3. Redman CW, Sacks GP, Sargent IL. Preeclampsia: An excessive maternal inflammatory response to pregnancy. Am J Obstet Gynecol 1999;180:499–506.
4. Roberts JM. Endothelial dysfunction in preeclampsia. Semin Reprod Endocrinol 1998;16:5–15.
5. Kuo C-C, Campbell LA. Detection of Chlamydia pneumoniae
in arterial tissue. J Infect Dis 2000;181: Suppl 3S432–6.
6. Moazed TC, Campbell LA, Rosenfeld ME, Grayston JT, Kuo CC. Chlamydia pneumoniae
infection accelerates the progression of atherosclerosis in apolipoprotein E-deficient mice. J Infect Dis 1999;180:238–41.
7. Hu H, Pierce GN, Zhang G. Atherogenic effects of chlamydia are dependent on serum cholesterol and specific to Chlamydia pneumoniae
. J Clin Invest 1999;103:747–53.
8. Fong IW, Chiu B, Viira E, Fong MW, Jang D, Mahony J. Rabbit model for Chlamydia pneumoniae
infection. J Clin Microbiol 1997;35:48–52.
9. Saiku P, Leinonen M, Mattila K, Ekman MR, Nieminen MS, Makela PH, et al. Serological evidence of an association of a novel chlamydia, TWAR, with chronic coronary heart disease and acute myocardial infarction. Lancet 1988;2:983–6.
10. Thom DH, Grayston ST, Sisovick DS, Wang SP, Weiss NS, Daling JR. Association of prior infection with Chlamydia pneumoniae
and angiographically demonstrated coronary artery disease. JAMA 1992;268:68–72.
11. Melnick SL, Shahar E, Folsom SR, Grayston JT, Sorlie PD, Wang SP, et al. Past infection by Chlamydia pneumoniae
strain TWAR and asymptomatic carotid atherosclerosis. Atherosclerosis Risk in Communities (ARIC) study investigators. Am J Med 1993;95:499–504.
12. Saikku P, Leinonen M, Tenkanen L, Linnanmaki E, Ekman MR, Manninen V, et al. Chronic Chlamydia pneumoniae
infection as a risk factor for coronary heart disease in the Helsinki Heart Study. Ann Intern Med 1992;116:273–8.
13. Ridker PM, Kundsin RB, Stampfer MJ, Poulin S, Hennekens CH. Prospective study of Chlamydia pneumoniae
IgG seropositivity and risks of future myocardial infarction. Circulation 1999;99:1161–4.
14. Nieto FJ, Folsom AR, Sorlie PD, Grayston JT, Wang SP, Chambless LE. Chlamydia pneumoniae
infection and incident coronary heart disease: The Atherosclerosis Risk in Communities Study. Am J Epidemiol 1999;150:149–56.
15. Strachan DP, Carrington D, Mendall MA, Ballam L, Morris J, Butland BK, et al. Relation of Chlamydia pneumoniae
serology to mortality and incidence of ischaemic heart disease over 13 years in the Caerphilly prospective heart disease study. BMJ 1999;318:1035–40.
16. Ostergaard L, Sorensen HT, Lindholt J, Sorensen TE, Pedersen L, Eriksen T, et al. Risk of hospitalization for cardiovascular disease after use of macrolides and penicillins: A comparative prospective cohort study. J Infect Dis 2001;183:1625–30.
17. Gupta S, Leatham EW, Carrington D, Mendall MA, Kaski JC, Camm AJ. Elevated Chlamydia pneumoniae
antibodies, cardiovascular events, and azithromycin in male survivors of myocardial infarction. Circulation 1997;96:404–7.
18. Gurfinkel E, Bozovich G, Daroca A, Beck E, Mautner B. Randomized trial of roxithromycin in non-Q-wave coronary syndromes: Roxis Pilot Study. Roxis Study Group. Lancet 1997;350:404–7.
19. Teppa RJ, Ness RB, Crombleholme WR, Roberts JM. Free leptin is increased in normal pregnancy and further increased in preeclampsia. Metabolism 2000;49:1043–8.
20. National High Blood Pressure Education Program Working Group. Report on high blood pressure in pregnancy. Am J Obstet Gynecol 1990;163:1689–712.
21. Grayston JT, Kuo CC, Wang SP, Altman J. A new Chlamydia psittaci
strain, TWAR, isolated in acute respiratory tract infections. N Engl J Med 1986;315:161–8.
22. Wang S-P. The microimmunofluorescence test for Chlamydia pneumoniae
infection: Technique and interpretation. J Infect Dis 2000;181:S421–5.
23. Fong IW. Antibiotics effects in a rabbit model of Chlamydia pneumoniae
-induced athersclerosis. J Infect Dis 2000;181: Suppl 3S514–8.
24. Siscovick DS, Schwartz SM, Caps M, Wang SP, Grayston JT. Chlamydia pneumoniae and atherosclerotic risk in populations: The role of seroepidemiology. J Infect Dis 2000;181: Suppl 3417–20.
25. Herrera JA, Chaudhuri G, Lopez-Jaramillo P. Is infection a major risk factor for preeclampsia? Med Hypotheses 2001; 57:393–7.
26. Roberts JM, Cooper DW. Pathogenesis and genetics of preeclampsia. Lancet 2001;357:53–6.
27. Meekins JW, Pijnenborg R, Hanssens M, McFadyen IR, van Asshe A. A study of placental bed spiral arteries and trophoblast invasion in normal and severe preeclamptic pregnancies. Br J Obstet Gynaecol 1994;101:669–74.
28. Wick G, Perschinka H, Millonig G. Atherosclerosis as an autoimmune disease: An update. Trends Immunol 2001; 22:665–8.
29. Ness RB, Roberts JM. Heterogeneous causes constituting the single syndrome of preeclampsia: A hypothesis and its implications. Am J Obstet Gynecol 1996;175:1365–70.
30. Christen S, Hagen TM, Shigenaga MK, Ames BN. Chronic inflammation, mutation, and cancer. In: Parsonnet J, ed. Microbes and malignancy. New York: Oxford University Press, 1999:35–88.
31. Kiechl S, Lorenz E, Reindl M, Wiedermann CJ, Oberhollenzer F, Bonora E, et al. Toll-like receptor 4 polymorphisms and atherogenesis. N Engl J Med 2002;347:185–92.
32. Ferrari M, Poli A, Olivieri M, Tardivo S, Biasin C, Balestreri F, et al. Seroprevalence of Chlamydia pneumoniae antibodies in a young adult population sample living in Verona. European Community Respiratory Health Survey (ECRHS) Verona. Infection 2000; 28:38–41.