Serum complement in eclamptogenic toxemia

The complement system and adverse pregnancy outcomes

Adverse pregnancy outcomes significantly contribute to morbidity and mortality for mother and child, with lifelong health consequences for both. The innate and adaptive immune system must be regulated to insure survival of the fetal allograft, and the complement system is no exception. An intact complement system optimizes placental development and function and is essential to maintain host defense and fetal survival. Complement regulation is apparent at the placental interface from early pregnancy with some degree of complement activation occurring normally throughout gestation. However, a number of pregnancy complications including early pregnancy loss, fetal growth restriction, hypertensive disorders of pregnancy and preterm birth are associated with excessive or misdirected complement activation, and are more frequent in women with inherited or acquired complement system disorders or complement gene mutations. Clinical studies employing complement biomarkers in plasma and urine implicate dysregulated complement activation in components of each of the adverse pregnancy outcomes. In addition, mechanistic studies in rat and mouse models of adverse pregnancy outcomes address the complement pathways or activation products of importance and allow critical analysis of the pathophysiology. Targeted complement therapeutics are already in use to control adverse pregnancy outcomes in select situations. A clearer understanding of the role of the complement system in both normal pregnancy and complicated or failed pregnancy will allow a rational approach to future therapeutic strategies for manipulating complement with the goal of mitigating adverse pregnancy outcomes, preserving host defense, and improving long term outcomes for both mother and child.

The Complement System in Pregnancy

Maternal recognition of fetal antigens is well-documented. Antibodies directed against fetal antigens are the rule rather than the exception. Maternal antibodies seem to bind fetal antigens at the placental level and apparently activate the complement system even in normal pregnancy, yet multiple studies confirm an increase in C1q, C4, C3 and CH50 levels in pregnancy and an absence of complement activation. More sensitive assays and a broadened concept of the timing of crucial immunologic events may lead to a greater understanding of the importance of the complement system in pregnancy.

Preeclampsia and pregnancies with small-for-gestational age neonates have different profiles of complement split products

OBJECTIVE

The activation of the complement system results in the generation of split products with pro-inflammatory properties. The objective of this study was to determine whether preeclampsia and small-for-gestational age (SGA) are associated with changes in the maternal plasma concentrations of anaphylatoxins C3a, C4a and C5a.

METHODS

A cross-sectional study was conducted in the following groups: (a) normal pregnant women (n = 134); (b) women who delivered an SGA neonate (n = 53); (c) preeclampsia with (n = 52) and without SGA (n = 54). Maternal plasma anaphylatoxin concentrations were determined by enzyme-linked immunoassay.

RESULTS

(1) Women with preeclampsia with or without SGA had a significantly higher median plasma C5a concentration than that of normal pregnant women and those with SGA alone (all P < 0.01); (2) women with SGA alone did not have an increase in plasma C5a concentration; (3) in contrast, the median maternal plasma concentration of C4a was lower in women with preeclampsia and SGA than that of those with a normal pregnancy (P = 0.001); (4) no changes in C3a were observed among the study groups.

CONCLUSION

Preeclampsia is associated with increased plasma concentration of C5a, regardless of the presence or absence of an SGA fetus. In contrast, there was no difference in the plasma C3a, C4a and C5a concentration in patients with SGA.

Immunological studies on pre-eclampsia in Nigerian women

Circulating immune complexes, C3b inactivator, C3 activator, C3c, C4 and C-reactive protein were assayed in 49 patients with pre-eclampsia and 35 apparently healthy pregnant Nigerian women. Pre-eclamptic women had significantly higher mean levels of circulating immune complexes, C3c and C-reactive protein. C3 activator mean level was also higher in pre-eclampsia than in normal pregnancy, C3b inactivator concentrations were greatly depressed and the mean level was also significantly lower in the pre-eclamptic group (P less than 0.001). However, C4 mean levels were the same in both groups. From the results, it is postulated that in pre-eclamptic conditions the significantly depressed levels of C3b inactivator could predispose to the persistence of deposited immune complexes in the kidneys, resulting in tissue damage. The findings also generally indicate an immunologic pathogenesis for the renal lesions in pre-eclampsia in Nigerian women.

Serum complement values (C3 and C4) to differentiate between systemic lupus activity and pre-eclampsia

It is often difficult to differentiate between an exacerbation of systemic lupus erythematosus (SLE) and intercurrent pre-eclampsia in a patient with SLE since the manifestations of both entities include proteinuria and hypertension. This study was undertaken to determine wether serum C3 and C4 values can help distinguish SLE activity from pre-eclampsia. In 21 nonpregnant women of child-bearing age, the mean C3 level was 124 +/- 5 mg/dl and the mean C4 was 31 +/- 1 mg/dl. In 24 normal women in the third trimester of pregnancy, the C3 and C4 levels were elevated (165 +/- 4 mg/dl, p less than 0.001 versus nonpregnant control women; 37 +/- 2 mg/dl, p less than 0.01 versus nonpregnant control women, respectively). In 17 women in the third trimester of pregnancy with documented pre-eclampsia, the mean C3 level was 162 +/- 4 mg/dl, no different from that in normal pregnant women (p less than 0.001 versus nonpregnant control women; p = NS versus normal pregnant women), and the mean C4 was 29 +/- 3 mg/dl, lower than that found in normal pregnant women (p less than 0.02 versus normal pregnant women). Antinuclear antibody was absent at titers of less than 1:20 in all of these pre-eclamptic patients. In contrast, pregnant women with SLE has significantly lower C3 (103 +/- 13 mg/dl) and C4 (15.3 +/- 3.6 mg/dl) values during the third trimester of pregnancy than either normal pregnant women (p less than 0.001 for C3 and C4) or women with pre-eclampsia (p less than 0.001 for C3 and p less than 0.004 for C4) during the third trimester of pregnancy. Of the eight women with SLE in whom serial complement values were determined, three had falling C3 or C4 levels, and in each, there was a flare of SLE activity either during or immediately after pregnancy. None of the five patients with a rising C3 concentration had a flare of disease activity; however, pre-eclampsia developed in one of these patients, characterized by hypertension and proteinuria. Thus, measurement of serum C3 and C4 can help differentiate between SLE activity and pre-eclampsia, since both C3 and C4 are significantly lower in women with SLE than women with pre-eclampsia, and serum C3 and C4 concentrations rise during uncomplicated or pre-eclamptic pregnancy in women with SLE.

Lupus pregnancy. II. Unusual pattern of hypocomplementemia and thrombocytopenia in the pregnant patient

To explore the causes of complications in pregnant women with systemic lupus erythematosus (SLE), we prospectively evaluated 34 pregnancies in 28 SLE patients, and 2 additional pregnancies in patients with lupus anticoagulant and positive antinuclear antibody, but no other manifestations of SLE. Nineteen pregnancies (55%) were complicated by marked proteinuria, thrombocytopenia, and/or lupus anticoagulant. Hypocomplementemia occurred in 18 pregnancies (52%). Neither thrombocytopenia-anticoagulant nor proteinuria was accompanied by an increase in antibody to double-stranded DNA or by clinical signs of active SLE. Antibody to Ro antigen did not predict fetal death. Both thrombocytopenia and proteinuria appeared abruptly during pregnancy and disappeared quickly after delivery. Fetal death was the result in 7 of 9 (77%) pregnancies in patients with anticoagulant, 6 of 10 (60%) in patients with thrombocytopenia, 6 of 18 (33%) in patients with hypocomplementemia, and 3 of 11 (27%) in patients with proteinuria. Twenty of 29 (68%) children were identified as male. The pathogenesis of hypocomplementemia was evaluated by a new assay, C1s-C1 inhibitor complex, which is thought to measure rate of complement activation by the classical pathway. Most pregnant patients with low CH50 levels and proteinuria had normal levels of C1s-C1 inhibitor complex, whereas nonpregnant patients with equivalent proteinuria and hypocomplementemia had high levels, as did pregnant patients with hypocomplementemia who did not have SLE. Pregnant and nonpregnant hypocomplementemic patients with proteinuria had similar levels of C3 and C4. In pregnant patients with SLE, C1s-C1 inhibitor complex was independent of CH50; in nonpregnant patients a linear relationship between C1s-C1 inhibitor complex and CH50 was seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunologic aspects of term pregnancy toxemia. A study of immunoglobins and complement

IgA, IgG, and IgM were measured by the single radial immunodiffusion method in umbilical cord and maternal sera in toxemia patients and in normal term pregnant cases. Complement (C' 3) levels were determined only in maternal sera. Quantitation of IgA, IgG, and IgM was performed in concentrated serial urine samples from three eclamptic and three normal control patients. Results show that there are lower IgG and IgM levels in the sera of mothers with toxemia of pregnancy; however, paradoxically higher IgM levels were detected in cord sera from their newborn infants without evidence of placental leakage or increased neonatal infection. The finding of the low IgG and IgM levels appears to be due in part to immunoglobin loss into the urine. The unchanged complement levels in toxemia, in this study, are not suggestive of an active immunologic process, but the high IgM in the newborn infants of toxemic mothers is unexplained and may represent active immunologic disease. Clearly, investigations of tissue binding and the formation of immunoglobin complexes should be carried out to better explain these abnormal findings.