Judith Forristal

Serum Complement Levels in Infancy: Age Related Changes

Summary: Levels of eight complement components and two control proteins, were determined on cord serum from normal full term neonates and serum from healthy infants aged 1 and 6 months. For all proteins, the levels were below the adult normal at birth and rose toward the adult range by age 6 months. In a second group of 271 patients, ages 1–36 months, serum Clq and properdin levels were measured. For both proteins, the mean values in early infancy were more than two SD below the adult range and did not reach the adult range until 18–21 months of age. The Clq concentration was more variable than that for any other component studied. In infants from 11 months-3 yr of age, Clq levels correlated with serum IgG levels, but properdin levels did not.Speculation: Low serum complement levels in neonates may contribute to their increased susceptibility to infections. Correlations between synthetic rates of Clq and IgG is suggested as the mechanism responsible for the correlation in serum levels of these proteins after age 1 yr.

Differences Between Membranoproliferative Glomerulonephritis Types I and III in Clinical Presentation, Glomerular Morphology, and Complement Perturbation

Data for 26 patients with membranoproliferative glomerulonephritis, type I (MPGN I) and 22 with membranoproliferative glomerulonephritis, type III (MPGN III), as distinguished by glomerular ultrastructure, were analyzed to determine differences in presentation, complement perturbation, and glomerular morphology by light microscopy. MPGN III was detected with greater frequency by the chance discovery of hematuria and proteinuria in the otherwise healthy individual (MPGN III, 63%; MPGN I, 30%; P = .01) and never, in the absence of renal failure, presented with systemic symptoms such as ease of fatigue, weight loss, and pallor, as may patients with MPGN I. The more frequent detection of MPGN III by chance is evidence that its onset is insidious and that for long periods it produces no symptoms or signs. Glomerular proliferation is also less than in MPGN I. Further, in MPGN III, the complement perturbation and glomerular immunofluorescence give no evidence of classical pathway activation, for which there is abundant evidence in MPGN I. Even with severe hypocomplementemia in MPGN III, C3 nephritic factor, another cause of hypocomplementemia, is rarely detectable and then in very low concentration. The cause of the complement perturbation in MPGN III has so far escaped identification. Although these observations give evidence that MPGN III is distinct from MPGN I, there is compelling evidence from other studies that a predisposition to both types is inherited and that similar genetic factors are operative in the two types. Because their genetic basis appears to be the same, it must be concluded that despite their differences, types I and III are variants of the same disease.

Patterns of Complement Activation in Idiopathic Membranoproliferative Glomerulonephritis, Types I, II, and III

Complement profiles on 22 hypocomplementemic patients with membranoproliferative glomerulonephritis (MPGN) type I, on 11 with MPGN II, and on 16 with MPGN III, gave evidence that the nephritic factor of the amplification loop (NFa) is responsible for the hypocomplementemia in MPGN II and the nephritic factor of the terminal pathway (NFt) for the hypocomplementemia in MPGN III. In contrast, in MPGN I, there was evidence for three complement-activating modalities, NFa, NFt, and immune complexes. As a result, four different patterns of complement activation were seen. NFa, found in MPGN II, produces a complement profile characterized mainly by C3 depression. In addition, four of seven (57%) severely hypocomplementemic MPGN II patients (C3 less than 30 mg/dL) had slightly depressed levels of factor B, and one of seven (14%) of properdin, but in all the C5 concentration was normal. In contrast, all eight severely hypocomplementemic patients with MPGN II had depressed C5 and properdin levels, and six of eight (75%) depressed levels of C6, C7, and/or C9. Of eight MPGN III patients with moderate hypocomplementemia, 50% had depressed C5 and properdin levels and the remainder, depressed C3 only. This spectrum of profiles is most likely produced by varying concentrations of NFt. In MPGN I, nine of 23 (39%) had a profile indicating only classical pathway activation; seven of 23 (39%), a pattern compatible with NFt alone; four of 23 (9%), evidence for both classical pathway activation and NFt; and three of 23 (13%), a pattern compatible with NFa. The unique multifactorial origin of the hypocomplementemia in MPGN I, often giving evidence of classical pathway activation, together with previously reported differences in glomerular morphology and clinical features at onset, makes it distinct from MPGN III. Depressed C8 levels were found to some extent in all hypocomplementemic states. The levels were uncommonly depressed in patients with NFa, most markedly depressed with NFt, and moderately reduced with classical pathway activation. The cause is not known. Diagnostically, profiles showing classical pathway activation and low levels of C6, C7, and/or C9 are specific for MPGN I. Those showing only classical activation are likewise diagnostic of MPGN I if systemic lupus erythematosus (SLE) and chronic bacteremia are ruled out.

Evidence for In Vivo Breakdown of β1C-Globulin in Hypocomplementemic Glomerulonephritis

Summary. Evidence has been obtained for the presence in vivo of alpha2Dglobulin, a breakdown product of serum f10-globulin, in patients with acute and persistent hypocomplementemic glomerulonephritis. The protein has been identified by immunoelectrophoretic analysis, and the amounts present have been determined by direct measurement of specific antigenic determinants present on alpha2D. 831A-Globulin, another breakdown product of Plcglobulin, may also be present in vivo in severely hypocomplementemic patients, but its levels are much lower than those of alpha2D-globulin. Alpha2D-globulin has been identified by immunoelectrophoretic analysis of fresh EDTA plasma from patients with hypocomplementemic nephritis as an arc in the alpha2 region that shows a reaction of identity with the arc representing alpha2D-globulin produced by aged normal serum. 831A-Globulin was not seen in these patterns. Measurement of specific antigenic determinants has been carried out in both fresh EDTA plasma and aged serum. In the fresh plasma, the concentration of D antigen, found on both Plw- and alpha2D-globulins, has been related to that of B antigen, found only on /31c and taken as a measure of the concentration of this protein. In the hypocomplementemic patients, the concentration of D antigen, in comparison to that of B, was greater than in the normal subjects. Similarly, in aged serum, the level of alpha2D was greater than would be expected from the amount of flic that had been broken down in vitro, measured by the concentration of ,81A. Calculations indicated that the in vivo alpha2D level in severely hypocomplementemic patients ranged from 7.5 to 18% of that which would be found in a pool of aged normal serum in which /3ic is completely broken down. The levels tended to be lower in less severely hypocomplementemic patients, and none could be detected in normal plasma. Only small quantities of A and D antigens are detectable in the urine of patients with hypocomplementemic nephritis. The rate of excretion is about equal to that of the normal subject. The study indicates that the low serum levels of fl3c-globulin that may be present over long periods in patients with persistent hypocomplementemic glomerulonephritis can be ascribed, in part, to in vivo breakdown of this pro

Hypocomplementemia of Membranoproliferative Nephritis DEPENDENCE OF THE NEPHRITIC FACTOR REACTION ON PROPERDIN FACTOR B

Membranoproliferative nephritis in children is frequently associated with a hypocomplementemia produced at least in part by C3 breakdown mediated by a circulating anticomplementary factor known as C3 nephritic factor (C3NeF). C3 breakdown by this factor in vitro requires the presence of a pseudoglobulin cofactor and magnesium. The present study provides evidence that properdin factor B (C3 proactivator) is activated in the nephritic factor reaction and is the direct mediator of C3 breakdown by C3NeF. Depletion of factor B from mixtures of normal human serum (NHS) and plasma from a patient with membranoproliferative nephritis (MPP), either by heating or by immune equivalence absorption, blocks C3 breakdown by C3NeF. Addition of purified factor B to these mixtures restores the anticomplementary effect. When purified factor B is added to mixtures of MPP and purified C3, breakdown also occurs. Associated with the C3 breakdown is a change in the electrophoretic mobility of factor B from the beta to the gamma position, a shift which has been associated with cleavage activation of the molecule. Further, serum factor B levels are often low in patients with membranoproliferative nephritis and bear a rough inverse correlation with C3NeF levels. It thus appears that factor B is the previously described heat-labile C3NeF cofactor. Whether the C3NeF reaction proceeds via a pathway comparable to that activated by the cobra venom factor or via that activated by zymosan or inulin cannot be determined from the present data.

Continuing C3 Breakdown after Bilateral Nephrectomy in Patients with Membrano-Proliferative Glomerulonephritis

Serum levels of complement components and of C3 nephritic factor (C3NeF) were measured serially in two patients with membrano-proliferative glomerulonephritis who were subjected to bilateral nephrectomy and maintained by peritoneal dialysis for 2 wk before renal transplantation. In both patients, low levels of C3 and high levels of preformed alpha 2D, a C3 breakdown product, were present before nephrectomy and remained essentially unchanged during the anephric period. With transplantation, C3 levels rose towards normal and alpha 2D disappeared from the serum. The serum of both patients contained detectable amounts of C3NeF, a factor which has been shown to react with a cofactor found in normal serum to form an enzyme, designated C3 lytic nephritic factor (C3LyNeF), which will cleave C3 to form the breakdown products, beta1A and alpha 2D. The level of C3NeF was high in one patient before nephrectomy, increased somewhat during the anephric period, and fell after transplantation. In the other patient, the C3NeF level was initially lower, remained relatively constant during the anephric period, and was not significantly affected by transplantation. In both patients, levels of C4 and C5 were either normal or elevated over the period of the study and bore no relationship to the C3 level. The following conclusions can be drawn from the data. The high levels of alpha 2D during the anephric period and the disappearance of this protein as C3 levels approach normal at the time of transplantation indicate that the low C3 levels were largely the result of C3 breakdown rather than diminished synthesis. The presence of C3NeF in detectable amounts in both patients suggest that C3LyNeF, formed by the reaction of C3NeF and cofactor, was responsible for the low C3 levels. Finally, the lack of effect of nephrectomy on C3, alpha 2D, and C3NeF levels indicate that the site of C3 breakdown was extrarenal and that C3NeF and cofactor are at least in large part of extrarenal origin.

Complement profiles in acute post-streptococcal glomerulonephritis

It is well known that the hypocomplementemia of acute post-streptococcal glomerulonephritis (APSGN) is characterized by markedly reduced serum concentrations of C3 and moderately reduced levels of C5 and properdin (P). However, the extent of the activation of the classical pathway is not well defined and only limited data are available concerning serum concentrations of terminal components other than C5. In serial serum specimens from 14 children with APSGN, the presence and extent of C4 activation was directly assessed by measurement by rocket immunoelectrophoresis for C4 and C4 (C4d/C4 ratio). Elevated values for this ratio, indicating C4 activation, were found in 8 of 14 of the initial serum specimens, and in some patients the ratio remained elevated for several weeks. In contrast, the serum C4 level was low in only 1 specimen (the specimen with the highest C4d/C4 ratio). However, in 10 patients C4 concentrations within the normal range rose in serial serum specimens. Serum C2 concentrations were depressed in the initial specimens from 5 patients. The concentrations of 13 other complement component and control proteins were also measured in these specimens. Levels of terminal components, other than C5, in the initial serum specimens were normal except for depressed C8 in 3 of 13 patients and depressed C6 in 1 of 14. Of these 4 individuals, 3 had the lowest C3 levels in the study. It is concluded that the classical complement pathway is frequently activated in patients with APSGN early in the condition and that subtle abnormalities in C6 and C8 levels occasionally occur.

The C3 nephritic factor andmembranoproliferative nephritis: Correlation of serum levels of the nephritic factor with C3 levels, with therapy, and with progression of the disease+

In the absence of corticosteroid therapy, the serum of all of 12 patients with membranoproliferative nephritis produced C3 breakdown which could be attributed, at least in part, to the C3 nephritic factor (C3NeF). Without therapy an inverse correlation between C3 and C3NeF levels was apparent in serial specimens; with steroid therapy this correlation was lost, and the levels of C3NeF tended to be lower and those of C3 higher. The lack of correlation with therapy is best explained by an effect of corticosteroid in diminishing the availability of cofactor. The data give no clear-cut evidence that the presence of high concentrations of C3NeF in the serum are associated with deterioration of renal function. If C3NeF does cause renal injury, the mechanism appears not to be directly dependent on the serum level of either C3 or C3NeF.

A “silent” phase of hypocomplementemic persistent nephritis detectable by reduced serum β1C-globulin levels

Two children are described who over long periods of time have had minimal or nolaboratory evidence of renal disease but have acute or subacute glomerulonephritis, as demonstrated by renal biopsy. An episode resembling acute glomerulonephritis occurred initially in each. Over a variable period, signs and symptoms of this episode subsided completely, but a markedly reduced serum level of β 1C -globulin has been consistently present. Continuing renal disease was suspected solely because of this abnormality.

Effect of the Nephrotic Syndrome on the Concentration of Serum Complement Components

The concentration of 12 component and four control proteins of the complement system was measured in serum from 43 children with a nephrotic syndrome, which subsequently proved to be steroid-responsive, and from 13 children with focal glomerulosclerosis (FGS) and was compared with values from 197 normal subjects. Of classical pathway complement components, 40% of patients had low C1q levels and 20%, low C2 levels. Mean serum levels of C1s, C4, C1INH, and C4bp were elevated. Of alternative pathway components, factors B and I were low in one third, while levels of C3 and H were commonly elevated. Of the terminal components, only C8 and C9 were low. In five patients with FGS with hypoalbuminemia without edema, all component levels were normal. With the exception of C1q, C1s, and C8, high molecular weight (mol wt) components were in high concentration and low mol wt components in low concentration. The three exceptions may be explained by the subunit structure of C1 and C8. From a practical standpoint, the study indicates that edematous patients with a nephrotic syndrome may have low serum levels of C1q and C2, simulating classical pathway complement activation such as commonly occurs in glomerulonephritis. However, low levels of C4, and possibly C1s, can be used as indicators of classical pathway activation since their levels are not reduced by a nephrotic syndrome.