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PubMed1979

Complement activation in asymptomatic patients with sickle cell anaemia.

Previous reports have suggested that a defect in serum complement may contribute to the increased susceptibility to infection shown by patients with sickle cell anaemia (SCA). In order to define the nature of any complement abnormality in SCA, we investigated the complement system in eighty-seven patients during asymptomatic periods, and analysed factor B turnover in a small sample. In these patients geometric mean serum concentrations of functionally active factor B and factor D, and of C3 and C4 protein (expressed as a percentage of normal reference serum) wer lower than in controls (78% vs 107%, P less than 0.001, 86% vs 103%, P less than 0.001, 91% vs 100%, P less than 0.01, 89% vs 105%, P less than 0.05 respectively). The ratio of the serum concentration of functionally active factor B to factor B protein was lower in patients than in controls (means 75% s.d. 16% vs mean 93%, s.d. 22% P less than 0.001), indicating a functional deficiency of factor B protein. In addition, the fractional catabolic rate of radiolabelled factor B was markedly increased in four out of seven asymptomatic patients studied, and was inversely related to the functional factor B concentration in serum (r = -0.59, P less than 0.05); factor B synthesis was uniformly increased. Complement activation was not related to the presence of circulating C1q binding material. We conclude that complement activation, rather than defective synthesis as previously suggested, contributes to the abnormalities in complement componenet concentration and function in asymptomatic subjects with sickle cell anaemia.

Adolescent↗
PubMed1975

Studies of the inhibition of C56-initiated lysis (reactive lysis). IV. Antagonism of the inhibitory activity c567-INH by poly-L-lysine.

The stable intermediate complex C56 can initiate the lysis (reactive lysis) of unsensitized erythrocytes (E) by the membrane attack machanism of complement. Certain serum constituents designated C567-INH inhibit reactive lysis by preventing the C567 complex, once formed, from attaching to a membrane surface. It is shown here that microgram quantities of poly-L-lysine (PLL), a synthetic polycation of molecular weight 180,000, can reverse the effests of C567-INH, and thereby potentiate formation of EC567 by erythrocytes, C56 and C7 in whole serum. Erythrocytes exposed to PLL in a preincubation step did not show either increased susceptibility to C567 or resistance to C567-INH, and reversal of C567-IHN by given amounts of PLL was not diminished as cell concentrations were greatly increased, indicating that the effect of PLL was predominantly directed against fluid phase rather than against erythrocyte membrane substrates. The effects of PLL and C567-INH were quantitatively reciprocal. Thus, PLL-induced potentiation of C56-induced lysis is a solute effect which seems to involve direct neutralization of naturally occurring serum inhibitors of the C567 trimolecular complex of complement. The use of PLL thus provides a suitable antagonist for C567-INH in reaction mixtures, and allows evaluation of the role of C567 and C567-INH in a variety of situations involving C-mediated lysis.

Alpha-Globulins↗
PubMed1979

[Complement and nephritic activity in membranoproliferative glomerulonephritis].

A study of complement profiles and of "nephritic activity" (NeF activity) has been carried out in 33 children presenting with membranoproliferative glomerulonephritis (MPGN), in order to determine the pathway of complement activation. By morphological studies two varieties of MPGN have been distinguished. In MPGN with subendothelial deposits, immunofluorescent studies and complement profiles show an activation by the classical pathway. The demonstration of NeF activity in 7 of 20 patients suggests that there is recruitment of the amplification pathway. In MPGN with dense deposits, immunopathological studies indicate an activation of the complement system through the alternate pathway, NeF activity being present in 10 of 13 patients. With the functional tests used, it is not possible to ascertain that the factors responsible for the NeF activity in MPGN with subendothelial deposits are identical to the C3NeF identified in MPGN with dense deposits and/or partial lipodystrophy.

Capillaries↗
PubMed1976

Complement-induced histamine release from human basophils. II. Mechanism of the histamine release reaction.

The activation of human serum complement by incubation with zymosan generates C5a which releases histamine from autologous basophils. The characteristics of the C5a-induced histamine release were investigated. It is similar to IgE-mediated reactions in requiring Ca++ and in being inhibited by EDTA. However, it has marked differences from IgE-mediated reactions. C5a, at all concentrations, released histamine completely in less than 2 min. The C5a reaction has a narrow pH optimum that antigen-induced release and occurs well at 17 degrees to 37 degreesC but not at 0 degreesC. The optimal reaction temperature is 25 degrees to 30 degrees C. Unlike the antigen-induced release, no two-stage activation with C5a for the release of histamine could be demonstrated. There was additive release between C5a- IgE-mediated reactions. Leukocytes could be desensitized to the C5a-mediated reaction by 1) incubating the cells at 37 degrees C for 45 min, 2) pretreating the leukocytes with activated serum in the presence of EDTA, and 3) adding the activated serum to the leukocytes at 0 degrees C before transferring to the optimal reaction temperatures. Cells desensitized to the complement-induced release have normal reactions to IgE-mediated histamine release. In parallel experiments, cells from allergic donors desensitized for IgE-mediated reactions by incubation with antigen under sub-optimal conditions release histamine normally upon the addition of C5a. The results indicate that histamine release by C5a involves a mechanism of basophil activation that is different from the pathway involved in the IgE-induced reaction.

Antigens↗
PubMed1984

The inhibitory effect of heparin and related glycosaminoglycans on neutrophil chemotaxis.

Clinical observations have shown that heparin has antiinflammatory activities. The effect of heparin on neutrophil chemotaxis was evaluated in vitro in the Boyden Chamber. This method enabled differentiation between the direct effects of heparin on neutrophil migration and locomotion, and its effects on chemotactic factors. Heparin inhibited both the random migration and directed locomotion of human neutrophils toward zymosan-activated serum (ZAS) and F-met-leu-phe (FMLP). Inhibition was found to be dependent on the concentrations of the heparin and of the chemotactic factors. No specific binding of heparin to the neutrophils could be demonstrated, and heparin's inhibitory effects were eliminated by simple washing of the cells. When added directly to the chamber containing chemotactic factor, heparin inhibited the chemotactic activity of ZAS but not that of FMLP, suggesting a direct inhibitory effect against C5a, the principal chemotactic factor in ZAS. Experiments performed with low-molecular-weight heparin, N-desulfated heparin, dextran sulfate, chondroitin sulfate and dextran indicated that the inhibitory effects of heparin on neutrophil chemotaxis are not related to its anticoagulant activity, but probably depend on the degree of sulfation of the heparin molecule.

Cell Movement↗
PubMed1984

Complement-induced expression of cryptic receptors on the neutrophil surface: a mechanism for regulation of acute inflammation in trauma.

We explored the hypothesis that identified changes in neutrophil function in patients with acute injury result from in vivo exposure to C5a. To evaluate this hypothesis, we performed a battery of tests on 26 trauma patients (14 with blunt injury, 12 with penetrating injury). Measured were plasma levels of the complement activation products C3a and C5a; neutrophil chemotaxis to C5a and N-formyl-methionyl-leucyl-phenylalanine (FMLP); neutrophil receptors for FMLP and C3b; and superoxide response to FMLP and serum-opsonized zymosan. Patient responses measured within 48 hours of admission were divided into two groups based on neutrophil migratory response to C5a. Patients unresponsive to C5a (but responsive to FMLP) showed elevated plasma C3a levels (248 +/- 6 ng/ml) compared with patients with normal C5a migratory response (104 +/- 8 ng/ml). FMLP receptor number was markedly increased in the chemotactically deactivated group (group I: 155,680 +/- 100; group II: 51,200 +/- 200) and receptor affinity was diminished. Binding activity of C3b increased in the C5a-unresponsive cells to 126% that of controls versus 94% for normally responsive patient cells. Superoxide production was found to be significantly increased in patient cells with increased receptor numbers. These results support the concept that a subgroup of trauma patients manifest plasma and neutrophil changes compatible with complement activation. The neutrophil changes identified demonstrate a state of cellular activation. The clinical significance of these results may reside in a risk of pulmonary microvascular injury if activated cells are marginated and then subsequently stimulated.

Chemotaxis, Leukocyte↗
PubMed1984

Various authentic chemoattractants mediating leukocyte adherence inhibition.

This study resulted from the finding that cancer extract-induced leukocyte adherence inhibition (LAI) depends on release of arachidonic acid metabolites of which leukotriene B4 (LTB4) is a chemoattractant. Leukotrienes, the chemotactic fragment of the fifth component of complement (C5a des arg), N-formyl-L-methionylyl-L-leucyl-L-phenylalanine (FMLP), platelet-activating factor (PAF), and phorbol myristate acetate (PMA) increased the nonadherence of human leukocytes to glass with bell-shaped dose-response curves. For maximum nonadherence, the optimum concentration was about 2 X 10(-11) M LTB4, 10(-9) M C5a des arg, 2 X 10(-8) M FMLP, 2 X 10(-9) M PAF, and 2 X 10(-8) M PMA. Of the adherent leukocytes, 29% became nonadherent. Higher concentrations of leukotriene E4, FMLP, PAF, and PMA induced leukocyte hyperadhesiveness. Chemoattractant-induced LAI was antagonized by inhibitors of glycolysis, oxidative metabolism, electron transport, microfilaments, and microtubules, whereas the same concentration of inhibitors did not alter the adherence of leukocytes to glass in control tubes. T-cells, neutrophils, and mononuclear cells showed LAI to LTB4, C5a des arg, and FMLP. Moreover, no additive effect was observed when leukocytes exposed to a first chemoattractant at its optimum concentration were exposed to a second. A competitive inhibitor of leukotriene slow-reacting substance of anaphylaxis, FPL 55712, blocked in a dose-response fashion LTB4-, C5a des arg-, and FMLP-triggered LAI. Eicosatetraenoic acid and nordihydroguaiaretic acid, cyclo-oxygenase-lipoxygenase pathway inhibitors, also markedly antagonized LTB4-, C5a des arg-, and FMLP-triggered LAI. Indomethacin (10(-5) M), piroxicam (10(-6) M), and aspirin, cyclooxygenase antagonists, negated LTB4-, C5a des arg-, and FMLP-induced LAI. Prostaglandins E2, E1, and F2 and prostacyclin did not trigger LAI. However, selective thromboxane synthetase antagonists completely negated chemoattractant-triggered LAI. Our studies indicated that chemoattractants stimulated leukocytes to produce thromboxanes, which increased leukocyte nonadherence.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1981

Human C5a des Arg increases vascular permeability.

C5a were generated in human plasma by incubation with zymosan in the presence of a carboxypeptidase B inhibitor. The carboxypeptidase inhibitor was added to prevent cleavage of the carboxyl terminal arginine from C5a and enabled it to be purified on the basis of spasmogenic activity on the guinea-pig isolated ileum. When injected into rabbit skin, purified C5a induced marked plasma leakage over a 30-min period, but only if the substance was first mixed with a vasodilator substance such as prostaglandin (PG)E2. The responses to C5a + PGE2 did not appear to be related to anaphylatoxic, histamine-releasing activity because an antihistamine, mepyramine, had only a small effect on plasma leakage. Further, removal of the carboxyl terminal arginine by carboxypeptidase B abolished activity on the ileum but not in the skin. The observation that both human C5a and C5a des Arg were able to increase vascular permeability in vivo suggested a parallel with leukotactic activity in vitro. In support of this, no responses to C5a + PGE2 were obtained in rabbits depleted or circulating polymorphonuclear leukocytes. Thus, inflammatory edema resulting from extravascular complement activation may be dependent on 2 components: a leukocyte/endothelial cell interaction triggered by C5a, and the concomitant generation of a vasodilator, prostaglandin.

Anaphylatoxins↗
PubMed1982

Basophil releasability in the newborn: factors limiting immunoglobulin E-mediated histamine release.

Cord basophil preparations from 53 term neonates were studied for various factors affecting immediate hypersensitivity reactions including: basophil IgE receptor density and histamine releasability following incubation with calcium ionophore A23187, zymosan-activated serum (C5a), and anti-IgE. Basophil histamine content (geometric mean, 0.4 pg/basophil, with content in 14/28 cord blood samples below 0.2 pg/cell) is considerably below that of atopic and nonatopic individuals (geometric mean, 2.3 pg/basophil). Histamine release is normal with both A23187 (range 33% to 88%) and C5a (range 11% to 58%). Normal release with anti-IgE was shown in five of nine cord blood samples (range 13% of 52%), but four of five cell preparations required IgE preincubation. Indirect evidence indicates that basophils from newborns contain less than 30,000 total IgE receptors/cell. IgE-mediated histamine release in basophils from newborns is minimized by suboptimal IgE binding. Optimal IgE binding is not favored in basophils from neonates because of low serum IgE and low IgE receptor density. Serum IgE and IgE receptors increase to a variable degree as the child grows older and may determine the clinical onset of allergic disease.

Adult↗
PubMed1982

Potentiation of the primary humoral immune response in vitro by C5a anaphylatoxin.

The effect of the anaphylatoxin C5a on the primary humoral immune response to SRBC was studied in culture of spleen cells from C3H mice. The addition of human C5a to antigen-stimulated cultures resulted in a significant, dose-dependent augmentation of the primary PFC response to antigen. The specificity of this effect was affirmed by the ability of C5ades Arg, but not of the structurally analogous C3a anaphylatoxin, to act in a parallel fashion. Enhancement could be observed over a range of doses of antigen. Brief preincubation of macrophages, but not of lymphoid cells, with C5a was sufficient to cause subsequent enhancement of the primary humoral immune responses. The duration of preincubation required for this effect closely paralleled that for binding of C5a to peritoneal cells. Immunopotentiation by C5a appears to involve the function of C5a receptor-bearing, Ia- accessory cells as well as Ia+ antigen-presenting cells. Immunopotentiation could be observed when the addition of C5a was delayed for up to 24 hr after initiation of culture. Additionally, augmentation of tritiated thymidine uptake in mixed lymphocyte reactions was enhanced by the addition of C5a in a fashion parallel to that for the primary response to SRBC. These observations support a role for C5a as a modulator of cellular immunity in addition to its role in acute inflammation. Possible cellular mechanisms and implications for immunomodulation of immune responses are discussed.

Adjuvants, Immunologic↗