Formation of C3a and C5a anaphylatoxins in whole human serum after inhibition of the anaphylatoxin inactivator.

Two biologically and chemically distinct anaphylatoxins (ATs) could be generated in whole human serum after removal of the AT inactivator (AI) by immune-absorption or after inhibition of AI with 1 M epsilon-aminocaproic acid (EACA). Both human ATs could be generated by treatment of serum with antigen-antibody complexes, which activate the classical complement pathway, and with inulin or yeast, both of which trigger the alternate pathway. The ATs were isolated from serum in active form and characterized as C3a and C5a. Although human C3a had been characterized previously, C5a had not. The molecular weight of human C5a AT was 17,500; its electrophoretic mobility at pH 8.5 was -1.7 x 10(-5) cm(2) V(-1) s(-1). The minimal effective concentration in vitro was 7.5 x 10(-10) M. The minimal effective doses of human C5a in producing a wheal and erythema in the human skin was 1 x 10(-15) mol. The results strongly suggest a biological function for both ATs and indicate that the expression of their activity is controlled by the AI of normal blood plasma.

Characteristics of a non-complement-dependent C3-reactive complex formed form factors in nephritic and normal serum.

When serum from a patient with membrano-proliferative glomerulonephritis and normal serum are mixed at 37 degrees C, C3 is rapidly broken down to two more rapidly migrating components. In the mixture, a heat-labile pseudoglobulin, designated as the C3 nephritic factor or C3NeF, reacts with a pseudogolbulin in the normal serum, designated as cofactor, to form a C3 inactivator. By analogy with the cobra venom factor, the C3 inactivator is most likely a complex of the nephritic factor and cofactor. The complex has been designated as the C3 lytic nephritic factor or C3LyNeF. The reaction which results in the Formation of C3LyNeF requires the presence of Mg(++), is highly temperature sensitive but occurs very rapidly at 37 degrees C. In 20 min at 37 degrees C, C3LyNeF can break down over 80% of the C3 in a mixture of normal and nephritic serum. The two-step reaction which leads to C3 breakdown has an optimum pH ranging from 6.0 to 9.0. Experiments employing serum depleted of C4 and C2, as well as certain characteristics of the C3NeF system provide evidence that C3 breakdown with nephritic serum is not dependent on complement-inactivating immune complexes or on the action of convertase (C4, 2). Data relating rate of C3 breakdown to the concentrations of C3NeF, C3, and C3LyNeF in the reaction mixture are similar to those for the reaction of enzyme with substrate. The biological significance of C3LyNeF in the production of glomerular inflammation has not been established.

A serum factor in chronic hypocomplementemic hephritis distinct from immunoglobulins and activating the alternate pathway of complement.

Nephritic factor (C3NeF) has been isolated from plasma of patients with hypocomplementemic chronic glomerulonephritis (HCG) by ion exchange and molecular sieve chromatography. This material was further treated with solidified anti-Ig antiserum. The purified material failed to react with antiserum to human IgG, IgG3, Fab, Fc, and kappa and lambda chains, but retained full C3NeF activity. The nonidentity of C3NeF with IgG was further demonstrated by Ouchterlony analysis using anti-IgG and anti-C3NeF. Isolated C3NeF was found to be a protein with a sedimentation coefficient of 7S and a mol wt of 150,000 daltons, which on microzone electrophoresis and gel electrophoresis at pH 8.6 behaved as a gamma-globulin. C3NeF is not a C1q precipitin and does not activate the classical complement pathway. Unlike cobra venom factor, it failed to enter into a complex with C3 proactivator (C3PA) when incubated with normal human serum (NHS) and then subjected to sucrose density gradient ultracentrifugation. The action of isolated C3NeF on C3 requires C3PA, C3PA convertase (C3PAse), and properdin (P). Similarly, C3PA conversion by C3NeF requires P, C3PAse, and C3. Total hemolytic activity was lost by incubation of 64 microg of C3NeF/1 ml NHS at 37 degrees C for 30 min. Both C3a and C5a anaphylatoxin could be generated by C3NeF in serum previously depleted of anaphylatoxin inactivator. Anti-C3NeF was found to detect an antigen in all NHS tested. Treatment of NHS with solidified anti-C3NeF caused impairment of the alternate complement pathway. It failed to sustain lysis of glutathione-treated human erythrocytes initiated by inulin. It is conceivable that the normal serum constituent which is removed by anti-C3NeF constitutes the inactive precursor of C3NeF, and a heretofore unrecognized component of the alternate pathway.

Serum C'3 lytic system in patients with glomerulonephritis.

The serums of patients with hypocomplementemic glomerulonephritis contain a substance that combines with a normal serum cofactor in the presence of magnesium ion to specifically cleave the third component of complement. This lysis of C'3 is 80 to 90 percent complete in 20 minutes at 37 degrees C and pH 7. Neither the nephritic factor nor its cofactor is identifiable with the complement system.

Circulating immune complexes after renal transplantation. Correlation of increased 125I-Clq binding activity with acute rejection characterized by fibrin deposition in the kidney.

To assess the role of circulating immune complexes in the pathogenesis of acute rejection, sera were measured for such complexes by the (125)I-C1(q) binding assay in 45 normal subjects, 24 allografted patients undergoing acute rejection, and in 11 allografted patients in a quiescent phase. Increased C1(q)-binding activity (C1(q)-BA) was detected in 14 patients with acute rejection, 9 of whom had renal biopsies showing fibrin deposition in the vasculature together with cellular infiltrates in the tubulo-interstitial structures; renal histology was not available in the other 5 patients. The other 10 patients with acute rejection, whose biopsies showed only cellular infiltrates, and the 11 patients in a quiescent phase posttransplantation did not have increased levels of serum C1(q)-BA. Of the group with increased serum C1(q)-BA, serial studies in eight patients showed a correlation between increased serum C1(q)-BA and the occurrence of rejection; with reversal by therapy, serum C1(q)-BA returned to within normal levels. Complexes from six patients were analyzed by sucrose density gradient ultracentrifugation to have sedimentation coefficients ranging from 15S to 18.4S. After acid dissociation and analysis by double-diffusion techniques, C1(q)-reactive complexes were shown to contain IgG. Immunofluorescent studies done in five renal biopsies from this group revealed granular deposits of immunoglobulin, and (or) less frequently, of complement in the glomeruli or the tubular basement membranes. The findings suggest that circulating immune complexes may mediate the type of acute rejection characterized by fibrin deposition in the kidney. The role of circulating immune complexes arising from the recipient's original kidney disease could be excluded in 10 patients with humoral rejection, inasmuch as the underlying renal pathology was of a "nonimmunologic" nature; this was corroborated by sequential studies in six patients in whom circulating immune complexes could not be demonstrated before rejection. The participation of administered antilymphocyte globulin (ALG) as an antigen also appears to be excluded in four patients, two who were not given ALG, and in two of whom episodes of rejection occurred unrelated temporally to ALG administration.

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.

Inhibition of C5 convertase by epsilon amino caproic acid (EACA): a limiting factor in the generation of C5a anaphylatoxin.

The effect of EACA on spontaneous C5 consumption and on the mechanisms of C5 activation through the alternative pathway of complement were analyzed. In contrast to the effect upon C3, ADDITION OF 1 M EACA to normal human serum (NHS) did not enhance spontaneous consumption of C5, but augmented its haemolytic efficiency. In the presence of 1 M EACA, activation of serum with zymosan (Z), resulted in inhibition of the formation of C5 convertase, and thus of C5 cleavage and C5a anaphylatoxin release. The generation of a C5 convertase on activated zymosan (Z) was inhibited when Z was formed at 17 degrees with NHS containing 1 M EACA. In contrast, if Z was formed in the absence of EACA the C5 convertase could be regenerated with fresh serum containing 1M EACA. Nearly maximal C5 consumption was obtained if 5 mM EGTA and 10 mM MgCl2 were added to the mixture. These conditions are considered optimal for generation and maximum recovery of fully active anaphylatoxin.

Serum complement levels in infancy: age related changes.

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.

Serum immune complexes in membranoproliferative and other glomerulonephritides.

Immune complexes were detected in the serum of patients with membranoproliferative glomerulonephritis (MPGN) Types I and II, systemic lupus erythematosus (SLE), and acute poststreptococcal glomerulonephritis (AGN) by sucrose gradient ultracentrifugation and by measurement of Clq binding activity (Clq-BA). Clq-BA was more sensitive in detecting complexes than was gradient ultracentrifugation. By gradient ultracentrifugation, the sedimentation velocities of the complexes in the three diseases were similar, ranging from 13S to 19S. This range corresponds to that observed by others in experimental chronic serum sickness nephritis. The complexes isolated by gradient ultracentrifugation always contained C3, usually IgG and C4, and in some patients with SLE and AGN, IgM. In MPGN, IgM and IgA could be present in glomerular deposits when not present in circulating complexes. In this disease also, serum complement levels were poor predictors of the presence of complexes. With increased Clq-BA, the levels of Clq, C4, and C2 could be normal or reduced and there was no correlation with C3 levels. With few exceptions, the clinical status of the patients with MPGN correlated well with Clq-BA.

Classical complement pathway activation in membranoproliferative glomerulonephritis.

Levels of components of the classical and alternative complement pathways and the activity of the C3 nephritic factor (C3NeF) were measured in serum specimens from patients with type I (subendothelial deposits) and type II (intramembranous dense deposits) membranoproliferative glomerulonephritis (MPGN) and the results compared with the levels in normal subjects. Although C3 and C5 concentrations were comparably depressed in type I and type II, the levels of Clq and C4 were lower in type I and the correlation coefficients between Clq vs. C4 and C4 vs. C3 were higher than in type II. The profile was highly suggestive of classical pathway activation. In contrast, in type II MPGN, factor B levels were lower and C3NeF activity was more frequently detectable and higher. A feature of interest was that type I, as compared to type II, was characterized by significantly lower serum concentrations of properdin, higher and more significant correlation coefficients between serum properdin concentrations and those of Clq, C4 and C3, and consistent glomerular deposition of properdin. The involvement of properdin in type I may reflect recruitment of a pathway resembling the C1 bypass mechanism, said to involve C1, properdin, factor B and C3-9.

Correlations between serum factor B and C3b inactivator levels in normal subjects and in patients with infections, nephrosis and hypocomplementaemic glomerulonephritis.

In normal subjects, factor B and C3b inactivator (KAF) levels were linearly related (r = 0-71); factor B levels in subjects with low normal levels of KAF were significantly lower than in those with high normal levels of KAF. This relationship is postulated to be the result of modulation by the level of KAF of the availability of nascent, spontaneously formed, C3b, in turn responsible for a constant low-grade activation of the C3b feedback which determines in part the level of factor B. The correlation did not obtain in patients with infections; levels of KAF and, to a greater extent, factor B were elevated. In patients with glomerulonephritis and hypocomplementaemic because of in vivo classical pathway activation, KAF and factor B levels were also poorly correlated, presumably because many factors were influencing the levels of these proteins transcending the modulating effect of the concentration of KAF. On the other hand, in patients with nephrosis and with MPGN Type II, KAF and factor B levels were low but were directly correlated. In nephrosis the correlation may be the combined result of an equal rate of catabolism of these proteins and of modulation of factor B levels by the level of KAF as in normal subjects. In MPGN Type II, the correlation may reflect the fact, noted in in vitro studies, that with alternative pathway activation, the level of KAF influences the extent of factor B and C3 conversion to a greater extent than when complement is activated by the classical pathway.

Purification and partial characterization of human and porcine C3a anaphylatoxin.

C3a anaphylatoxin is a protein fragment generated enzymatically in serum during activation of the third component of complement (C3). A four-step procedure is described for the purification of human and porcine C3a anaphylatoxins from their respective sera after activation with inulin. Because serum carboxypeptidase rapidly inactivates C3a, the inhibitor epsilon-aminocaproic acid (EACA) was added during C3 activation, thus permitting isolation of fully active C3a anaphylatoxins directly from serum. A 2000-fold purification of C3a was achieved with an average 30% recovery assuming total conversion of C3 during treatment of serum with inulin. Human C3a anaphylatoxin obtained through the action of the C3 activating enzyme of the "alternate" pathway appeared nearly identical with the C3a obtained from isolated C3 after treatment with the C4,2 enzyme of the "classical" pathway or with trypsin. Comparisons were made between various properties of human and porcine C3a anaphylatoxins. The molecular weights differed only slightly. Electrophoresis on a cellulose acetate strip at pH 8.6 indicated a difference of approximately one net charge between human and porcine C3a, with the human anaphylatoxin exhibiting the more basic behavior. Although the amino acid compositions are similar, significant differences exist. The most marked difference was the total absence of threonine residues in porcine C3a. The NH2-terminal sequences of 20 amino acid residues were examined; homology existed for 16 of the 20 positions. Although partial analysis of the primary structure of human and porcine C3a indicates approximately 80% homology, no immunological cross-reactivity between the anaphylatoxins could be detected with antisera produced to either human or porcine C3a. In spite of the structural differences, the biological activities of porcine and human C3a were essentially identical. Smooth muscle contraction, increase in vascular permeability, and release of histamine from mast cells were similarly induced by equal amounts of anaphylatoxin from either human or porcine origin. Porcine C3a, like human C3a, was shown to contain a COOH-terminal arginyl residue essential for smooth muscle contraction and for induction of histamine release from mast cells. The sequence adjacent to the COOH-terminal arginine was Leu-Ala-Arg-COOH for both humans and porcine C3a. Current evidence suggests common mechanisms exist for the generation of C3a in various animal species and that the two known C3 activating enzymes in serum exhibit trypsin-like specificity.