The cytotoxic action of immune gamma globulin and complement on Krebs ascites tumor cells. II. Chemical studies

Complement C5b-9 and Cancer: Mechanisms of Cell Damage, Cancer Counteractions, and Approaches for Intervention

The interactions of cancer cells with components of the complement system are highly complex, leading to an outcome that is either favorable or detrimental to cancer cells. Currently, we perceive only the "tip of the iceberg" of these interactions. In this review, we focus on the complement terminal C5b-9 complex, known also as the complement membrane attack complex (MAC) and discuss the complexity of its interaction with cancer cells, starting with a discussion of its proposed mode of action in mediating cell death, and continuing with a portrayal of the strategies of evasion exhibited by cancer cells, and closing with a proposal of treatment approaches targeted at evasion strategies. Upon intense complement activation and membrane insertion of sufficient C5b-9 complexes, the afflicted cells undergo regulated necrotic cell death with characteristic damage to intracellular organelles, including mitochondria, and perforation of the plasma membrane. Several pro-lytic factors have been proposed, including elevated intracellular calcium ion concentrations and activated JNK, Bid, RIPK1, RIPK3, and MLKL; however, further research is required to fully characterize the effective cell death signals activated by the C5b-9 complexes. Cancer cells over-express a multitude of protective measures which either block complement activation, thus reducing the number of membrane-inserted C5b-9 complexes, or facilitate the elimination of C5b-9 from the cell surface. Concomitantly, cancer cells activate several protective pathways that counteract the death signals. Blockage of complement activation is mediated by the complement membrane regulatory proteins CD46, CD55, and CD59 and by soluble complement regulators, by proteases that cleave complement proteins and by protein kinases, like CK2, which phosphorylate complement proteins. C5b-9 elimination and inhibition of cell death signals are mediated by caveolin and dynamin, by Hsp70 and Hsp90, by the mitochondrial stress protein mortalin, and by the protein kinases PKC and ERK. It is conceivable that various cancers and cancers at different stages of development will utilize distinct patterns of these and other MAC resistance strategies. In order to enhance the impact of antibody-based therapy on cancer, novel precise reagents that block the most effective protective strategies will have to be designed and applied as adjuvants to the therapeutic antibodies.

Immune cytolysis: electron microscopic localization of cellular antigens with ferritin-antibody conjugates

Immune gamma globulin has been coupled to ferritin by the diisocyanate method of Singer. The final product ("ferroglobulin") had approximately 13 per cent of its gamma globulin coupled to ferritin, and roughly half of its ferritin coupled to gamma globulin. The uncoupled gamma globulin could be removed by ultracentrifugal sedimentation of the free ferritin and the ferritin-antibody conjugates. The characteristics of the native antibody were retained by the ferritin-antibody conjugates, for they could be precipitated by anti-gamma globulin antisera, and when used as antibodies, they reacted specifically with soluble and cellular antigens. Ferroglobulin preparations made from rabbit antisera against whole ascites tumor cells were incubated with the cells, and the location of ferritin determined by electron microscopy of thin-sectioned material. It was found that the immune ferroglobulins localized specifically on antigens of the cell membrane. Some of the ferritin label entered the cells by pinocytosis, but the ferritin-antibody units did not appear able to pass directly through the cell membrane into the cytoplasmic matrix. When cells were incubated with ferritin-labeled antibody and complement, antibody could be located in the cytoplasmic matrix, and it therefore appeared that complement action was required before antibody could pass directly through the cell membrane. This finding was consistent with previous observations that the plasma membrane of an antibody-complement treated cell becomes permeable to large molecules. In broken cell preparations incubated with ferroglobulin, antibody combined with amorphous material and with structures derived from cell membranes and from smooth membranes of the endoplasmic reticulum. The data favor the concept that antigens contained within the membranous structures are most important in the formation of cytotoxic antibodies. The reported experiments support the view that cytotoxic antibodies fix primarily to surface antigens of the cell membrane. The subsequent action of complement establishes the permeability defect that induces the osmotic lysis of the cell and permits antibody to pass into the cell where it may act in a similar fashion on intracellular organelles.

Chromatographic resolution of the first component of human complement into three activities

A euglobulin fraction of human C'1 has been chromatographically resolved into three distinct activities, designated C'1q, C'1r, and C'1s, in the order of their elution from DEAE cellulose. All three of these activities have been shown to participate in various hemolytic reactions requiring C'1, including the cold phase of the Donath-Landsteiner reaction, and to be necessary for generation of C'1 esterase. C'1q was identical with a previously described serum protein implicated in a very early step of complement action and designated the 11S component on the basis of its sedimentation constant. C'1r could not be related to a known complement activity and has been presented as a new component. C'1s, on the basis of chromatographic evidence, was identified with C'1 proesterase. Methods of assay of these components of C'1 have been presented. The significance of C'1q, C'1r, and C'1s in generation of C'1 esterase and the central role of this enzyme in reactions involving C'1, C'4, and C'2 have been discussed.

Immune cytolysis. 1. The release of ribonucleoprotein particles. 2. Membrane-bounded structures arising during cell fragmentation

It has been shown that Krebs ascites tumor cells incubated in vitro with immune gamma globulin and complement lose the bulk of their cytoplasmic RNA to the suspending medium, although the cell membrane remains visibly intact. The present experiments show that about four-fifths of the lost RNA is sedimented by centrifugation of the cell-free medium at 105,000 g. Electron microscopic and chemical analyses of the pellets show them to consist of 150 A ribonucleoprotein particles. It is concluded that most of the RNA passes from the cells in this form. Antibody-complement action causes osmotic swelling of the tumor cells and they become quite fragile. Fragmentation of such preparations yields large numbers of membrane-bounded spheres which may be separated from the heavier nuclei by differential centrifugation. Electron microscopic study of the spheres provides evidence that they can arise from segments of the cell surface as well as from mitochondria and the endoplasmic reticulum.

Studies on immune cellular injury. I. Cytotoxic effects of antibody and complement

A model system for the investigation of immune cellular injury in primary isolates of a fixed-tissue cell of human origin has been described, using metabolism-inhibition and uptake of trypan blue as independent criteria of cytoxicity. Cytotoxic effects on human amnion cells were produced by the combination of specific rabbit antibody and factors in normal human serum which were indistinguishable from the components of hemolytic complement and calcium and magnesium ions. The data have been discussed in relation to the apparent multiplicity of serologic systems which can effect cellular injury. The nature of the cell and the source of antibody or normal serum constituents have been emphasized as factors which may influence the experimental selection of a given humoral mechanism.

Effect of antibody and complement on permeability control in ascites tumor cells and erythrocytes

Rabbit antibody + complement alters the permeability properties of mouse Krebs ascites tumor cells and erythrocytes. When antibody + C' acts on ascites tumor cells in a low protein medium, intracellular K⁺ is lost from the cells at a rate far greater than the normal leak rate. At the same time the cells lose amino acids and ribonucleotides and become fully permeable to the Na⁺ of the medium. When antibody + C' acts in a low protein medium, the cells swell extensively and lose most of their macromolecules to the medium (hemoglobin from erythrocytes, protein and RNA from the ascites tumor cells). If the antibody + C' acts in a medium containing protein in sufficient concentration to balance the colloid osmotic pressure of the cells, the swelling is prevented; no macromolecules are then lost from the cells, but the loss of K⁺ and entrance of Na⁺ are not altered, and the loss of amino acids and ribonucleotides is only slightly affected. It therefore appears that the action of antibody + C' is to produce functional "holes" in the animal cell membrane which permit the equilibration of cations and small molecules between cell and medium. This leads to an increase in the osmotic pressure of the cell and a rapid influx of water. The cell membrane and its "holes" are thereby stretched, permitting macromolecules to escape from the cell.

IMMUNO-ELECTRON MICROSCOPE ANALYSIS OF THE SURFACE LAYERS OF THE UNFERTILISED SEA URCHIN EGG. I. EFFECTS OF THE ANTISERA ON THE CELL ULTRASTRUCTURE

The response of unfertilised Paracentrotus lividus eggs to γ-globulin fractions of antisera against isolated homologous jelly coat substance or homologous homogenates of jellyless eggs has been studied at the ultrastructural level. The antijelly γ-globulin caused precipitation of the jelly layer, the density of precipitation varying between different eggs and being proportional to the γ-globulin concentration. Agglutination of the jelly substance of adjacent eggs, which is species specific, occurred frequently with higher γ-globulin concentrations. Antiegg γ-globulins (from antiserum against total homogenates of jelly-free eggs or the heat-stable fraction thereof) did not produce these effects. Instead, these γ-globulins caused various structural alterations mostly representing stages in parthenogenetic activation. This species-specific activation was induced by the reaction of antibodies with some heat-stable egg antigens different from those involved in jelly precipitation. Surface alterations included the formation of small papillae, membrane blisters, hyaline layer, and activation membrane, the release of material from the cell surface, and the breakdown of cortical granules. These alterations were dependent on both γ-globulin concentration and the variable reactivity among different females. Aster formation, found intracellularly, verified that the surface responses represented real parthenogenetic activation and were not the result of immune lysis. No such alterations appeared in the controls.

Trypanosoma brucei: biochemical and morphological studies of cytotoxicity caused by normal human serum

The biochemical and morphological events which accompany lysis of Trypanosoma brucei by normal human serum have been described. The prelytic events include loss of infectivity and rapid cation shifts across the cell membrane. This is followed by cell swelling, fraying of the surface coat of the cell, loss of intracellular organelles, and eventually cell lysis. The data presented are consistent with a colloid osmotic mechanism of lysis induced by irreversible acute damage to the normal permeability properties of the trypanosome plasma membrane.

A convenient and sensitive cytotoxicity assay for macrophage activating factor

A convenient procedure is described for assaying macrophage activating factor (MAF) in lymphokine preparations. This procedure utilizes thioglycollate-elicited peritoneal macrophages from C57BL/6J mice as effector cells and [3H]thymidine-labeled L929 target cells. A novel component of the cytotoxicity assay is the inclusion of a 20 min terminal incubation of the cultures with 10 micrograms/ml pancreatic deoxyribonuclease to facilitate the release of radioactivity from killed target cells. This method routinely gives a 10-20-fold greater release of [3H]thymidine from cultures containing MAF than from cultures containing macrophages and target cells alone. Additional advantages of this procedure are that it is relatively rapid, killing can be monitored microscopically, and MAF assays can be performed using macrophage concentrations as low as 1 X 10(5)/cm2, using effector to target cell ratios as low as 1:1, and using lymphokine dilutions of 10(-3) - 10(-4).

Optimal strategies in immunology III. The IgM-IgG switch

During a primary immune response generally two classes of antibody are produced, immunoglobulin M (IgM) and immunoglobulin G (IgG). It is currently thought that some lymphocytes which initially produce IgM switch to the production of IgG with the same specificity for antigen. During a secondary immune response IgG is the predominant antibody made throughout the response. In this paper we address the question of why such apparently complicated modes of response should have been adapted by evolution. We construct mathematical models of the immune response to growing antigens which incorporate complement dependent cell lysis. By comparing the times required to eliminate antigen we show that under certain conditions it is advantageous for an animal to switch some of its lymphocytes from IgM to IgG production during a primary response, but yet to secrete only IgG during a secondary response. The sensitivity of such a conclusion to parameter variations is studied and the biological basis and implications of our models are fully discussed.

Characterization of membrane permeability alterations induced in Vero cells by Clostridium perfringens enterotoxin

Alterations in plasma membrane permeability induced by Clostridium perfringens enterotoxin were studied using Vero (African green monkey kidney) cells which were radioactively labeled with four markers of different molecular size. The markers were alpha-amino[14C]isobutyric acid (Mr 103), 3H-labeled nucleotide (Mr approx. 300), 51Cr label (Mr approx. 3000) and [3H]RNA (Mr>25000). Over a 2h period, enterotoxin caused significant release of aminoisobutyric acid, nucleotides and 51Cr label but not RNA. The effects of enterotoxin on label release were dose- and time-dependent. The rate of release of markers was dependent upon their size. Permeability alterations could be detected within 15 min with a high dose of enterotoxin. Gel chromatography of released material was used to determine that markers of Mr 3000 but not 25000 leaked from permeabilized cells. It was concluded that enterotoxin is producing functional 'holes' of limited size in the membrane. Permeability changes due to enterotoxin treatment differed between confluent and nonconfluent (growing) cells. We propose that the primary action of the enterotoxin is to interact with the plasma membrane and produce functional 'holes' of defined size. The resultant alterations in membrane permeability cause the loss of essential cellular substances which inhibits processes such as macromolecular synthesis and eventually leads to cell deterioration and death.

Mechanisms of tumor immunity. An overview

The involvement of the immune system in the host response to tumors is complex and involves both lymphocytes and lymphocyte-derived mediators, as well as inflammatory cells and various other agents such as complement. These activies are not confined to cytodestructive processes; recent studies demonstrate that the migration characteristics of tumor cells may be modified by immunologically derived substances. The multiplicity of possible immune system-neoplastic cell interaction is unfortunately balanced by the multiplicity of mechanisms that serve to interfere with an effective immune response to tumors. These mechanisms may reflect pathologic derangements of normal immunoregulatory processes or may involve the production of suppressive substances by the tumors themselves. In either case, a number of genetic and other predisposing factors must contribute to the ultimate resolution of the battle between host and tumor. Successful strategies for immunologic intervention must take these parameters into account.

Role of complement in the toxicity of dietary legumes

On the basis of in vivo data Jayne-Williams (1) has proposed that the toxicity of dietary legumes is due to their content of lectins which are immunosuppressive. On the basis of in vitro data with cultured lymphocytes (2), it is now proposed that ingested lectins bind to cell surfaces and cause autologous complement components to bind to and destroy immunologically competent cells. The hypothesis throws a possible light on the aetiology of favism and Whipple's disease.

Experimental immune pancreatitis in the mouse by rabbit immune sera directed against purified enzymes of the exocrine pancreas

An experimental xenogeneic immune pancreatitis was induced in AB-mice by repeated intraperitoneal injections of rabbit immune sera directed against purified pancreatic enzymes (alpha-amylase, lipase, trypsin) for 3 hours up to 8 days. Histologically, the immune pancreatitis is characterized by three different findings: 1. Multiple acinar cell necroses on the 2nd, 3rd and 5th day of immune serum application. 2. A dedifferentiating acinar cell atrophy with development of pseudocanalicular acini on the 5th and 9th day. 3. An increasing interstitial histiolymphoplasmocytic pancreatitis on the 5th and 9th experimental day. Ultrastructurally, the acinar cell necroses proved as the final stage of a step-by-step developing acute lethal cell damage. The dedifferentiating acinar cell atrophy corresponds to a chronic sublethal cell injury with alteration of different cytoplasmic components. The interstitial pancreatitis in immune serum treatment is characterized by differently activated histiocytes and lymphocytes as well as by mature plasma cells. Because of immune histological findings (peri- and intraacinar deposition of rabbit globulin, specific fixation of guinea-pig complement, and appearance of mouse globulin in the mouse exocrine pancreas) and control experiments with rabbit and mouse normal serum as well as with physiological saline, the pathogenesis of the induced xenogeneic immune pancreatitis is regarded as a twophase process: 1. The acinar cell necroses are mainly due to a cytotoxic immune reaction (possibly in combination with an immune complex reaction) caused by specific anti-pancreatic enzyme antibodies of the applied immune sera. The dedifferentiating acinar cell atrophy may be the result of a specific action of the anti-enzyme antibodies against the corresponding pancreatic enzymes in the apical secretion granules of the pancreatic acinar cells. 2. The interstitial histiolymphoplasmocytic pancreatitis is mainly the morphologic substrate of an extravascularly (intraperitoneally) induced serum sickness reaction (immune complex reaction) due to the foreign proteins applied with the xenogeneic immune sera.

Successful short-term modification of hyperacute renal allograft rejection in the primate. Intrarenal effects of phenoxybenzamine and methylprednisolone combined with heparin

Inhibition of renal vasoconstriction during hyperacute rejection by phenoxybenzamine or methylprednisolone combined with either the antiplatelet agent pyridinolcarbamate or heparin was evaluted in primates. Phenoxybenzamine plus pyridinolcarbamate did not prolong kidney survival. Phenoxybenzamine plus heparin uniformly prolonged low rates of venous flow to 180 minutes and delayed secondary C3 consumption, sequestration of erythrocytes and platelets, coagulation, and fibrinolysis; neutrophil sequestration and vascular injury and obstruction were more marked than with heparin alone. Host pretreatment with methylprednisolone plus heparin also prolonged the low rates of venous flow to 180 minutes, further reduced secondary alterations, and resulted in the least vascular injury. When intact donor kidneys were also pretreated with methylprednisolone, persistently normal rates of venous flow were achieved. Despite marked consumption of Factor XII, the consumption of C3, other coagulation factors, prekallikrein, and sequestration of formed elements was minimal, and the histology appeared compatible with even more prolonged survival.

Sensitive assay for detection of toxin-induced damage to the cytoplasmic membrane of human diploid fibroblasts

A sensitive assay was developed for detection and quantitation of subtle permeability changes in the cytoplasmic membrane of human diploid fibroblasts. Release of the non-metabolizable amino acid [1-14C]alpha-aminoisobutyric acid (AIB; molecular weight (103) from the cytoplasm of prelabeled cells was used as an indicator of toxin-induced membrane damage. An optimal procedure for labeling these cells was designed after varying the conditions with regard to pH, temperature, concentration of AIB, composition of medium, and incubation time. Toxin-induced release of AIB was compared with release of a previously described nucleotide label, [3H]uridine. Melittin from bee venom and the polyene antibiotics filipin and amphotericin B in low concentrations induced a strikingly greater release of AIB than of nucleotide label. The sensitivity of this assay was furthermore demonstrated by treatment with the following bacterial cytolysins: phospholipase C and theta-toxin from Clostridium perfringens, alpha-, beta-, delta-, and gamma-toxins from Staphylococcus aureus, and streptolysin S from Streptococcus pyogenes. In spite of their different modes of action, all these membrane-active toxins at low concentrations induced a significant release of AIB label. For an equal release of nucleotide label, several times higher concentrations were required.

Determination of toxin-induced leakage of different-size nucleotides through the plasma membrane of human diploid fibroblasts

Human diploid lung fibroblasts were treated with cytolytic bacterial toxins and the nature of the membrane damage was investigated. [3H] uridine was used for differential labeling of cytoplasmic components of small or large molecular size. Two principal size categories were achieved by labeling the fibroblasts in either early growth phase or stationary phase, a high-molecular weight ribonucleic acid label and a low-molecular-weight nucleotide label. The size of the labeled molecules was determined by perchloric acid precipitation and gel chromatography. Leakage of labeled molecules of different size indicated the size of the "functional pores" in the plasma membrane caused by the test substance. The nonionic detergent Triton X-100 produced large functional pores in the fibroblast membrane as evidenced by rapid leakage of both large and small labeled molecules. Theta-toxin from Clostridium perfringens and the polyene antibiotic filipin both gave rise to considerably small functional pores in the plasma membrane. Although small molecules easily passed the treated membrane, large molecules could not escape from the cells even after prolonged treatment with these substances or by increasing their concentration. By the contrast, the leakage profiles obtained with melittin from bee venom or with delta-toxin from Staphylococcus aureus in each case suggested the formation initially of pores of intermediate size that increased upon prolonged incubation or when higher concentrations were used.

Serum factors affecting the incorporation of (3H)thymidine by lymphocytes stimulated by antigen. II. Evidence for a role of complement from studies with heated serum

Lymph node cells from preimmunized rabbits were cultured with varying concentrations of antigen in autologous serum which had been collected before immunization. [³H]Thymidine was added after 18 hours of culture and the cells were harvested at 24 or 66 hours for the determination of the radioactive labelling of acid-precipitable material.

Preheating serum (56°, 20 minutes) enhanced labelling in both control and antigen-treated cultures. This `heat effect' had an early (24 hour) non-specific component, independent of antigen concentration, and a late (66 hour) specific component which was most evident at high antigen concentrations. The conditions of preheating serum (temperature and time) required to produce the heat effect were similar to those required to remove haemolytic activity against rat erythrocytes. However, at certain temperatures and times there were discrepancies. These discrepancies, and data from experiments in which preheated and unheated sera were mixed in varying proportions, or interchanged in different sequences, were explicable on the basis of (i) a requirement for complement in stoichiometric quantities dependent on the number of cells being inhibited, (ii) the involvement of the majority of the cultured cells in the early non-specific component of the heat effect, but only cells capable of proliferating in response to added antigen in the late specific component, (iii) the secretion of complement by cultured cells.

Preheating serum (66°, 20 minutes) depressed labelling in control and antigen-treated cultures and reduced agglutinating activity against both autologous and heterologous erythrocytes.

The results are discussed in relationship to models which require that the size of a specific lymphocyte clone be positively or negatively regulated by the concentration of antigen specific for that clone. With increasing antigen concentration three effects on cells bearing specific receptor sites are distinguished. (i) Cell stimulation under conditions of antigen concentration and cell receptor specificity such that only a few antigen molecules can bind to cells. (ii) Complement-dependent inhibition under conditions such that more antigen molecules can bind to cells. (iii) Complement-independent inhibition under conditions, possibly unphysiological, such that very large quantities of antigen molecules can bind to cells.

Serum factors affecting the incorporation of (3H)uridine by lymphocytes stimulated by concanavalin A. Studies of the role of complement

1. Rat lymph-node cells cultured in serum and medium 199 were activated to transform and proliferate by concanavalin A. Initial cell activation was assessed by measuring the enhanced radioactive labelling of cells with [(3)H]uridine produced by concanavalin A during the first 6h of culture. 2. In medium containing serum the degree of activation was dependent on the ratio of concanavalin A to non-diffusible serum macromolecules; however, cells could be activated to a normal extent in a medium containing only diffusible molecules. This indicates that certain serum macromolecules buffer cell receptor sites against reaction with concanavalin A. 3. At high concanavalin A concentrations labelling was depressed below that of control cultures without concanavalin A. This inhibition of labelling (i) occurred in calf serum, but not in homologous serum, (ii) was removed by pretreatment of serum with various complement inhibitors, and (iii) first appeared after 1h of culture following an initial phase of cell activation by concanavalin A. Cells pre-labelled with [(3)H]uridine slowly released the label into the culture medium; this rate of release was suddenly accelerated after 1h of culture with concanavalin A if complement was present. The results suggest that inhibition of labelling requires the sequential binding of concanavalin A and then complement to the cell surface. 4. Results from experiments in which calf serum was mixed in various proportions with calf serum which had been preheated to inactivate complement, suggest (i) a requirement for complement in stoicheiometric quantities dependent on the number of cells being inhibited, and (ii) that preheated serum can inactivate complement in unheated serum. 5. The proliferative response over 3 days of culture was assessed by measuring the enhanced labelling of cells with [(3)H]thymidine produced by concanavalin A. In preheated calf serum two types of inhibition were noted. (i) A progressive inhibition at high concanavalin A concentrations so that the optimum response was shifted to lower concanavalin A concentrations as the duration of culture was extended; it is suggested that this reflects the secretion of complement by cultured cells. (ii) An inhibition of the optimum response appearing late in the culture period at high cell concentrations; it is suggested that this is due to the exhaustion of medium nutrients in most actively growing cultures.

Lysosome and phagosome stability in lethal cell injury. Morphologic tracer studies in cell injury due to inhibition of energy metabolism, immune cytolysis and photosensitization

In two types of cell injury in a tissue culture system, the possibility was tested that lysosome rupture may be a lethal cellular reaction to injury, and thus an important general cause of irreversibility of damage in injured tissue. Prior labeling of secondary lysosomes with the fluorochrome acridine orange, or with ferritin, was used to trace changes in lysosomes after applying an injury. The metabolic inhibitors iodoacetate and cyanide were used together to block the cell's energy supply, or attachment of antiserum and subsequent complement attack were used to damage the surface membrane, producing rapid loss of cell volume control. Living cells were studied by time-lapse phase-contrast cinemicrography and fluorescence microscopy, and samples were fixed at intervals for electron microscopy. The cytolytic action of complement was lethal to sensitized cells within 2 hours, but results showed that lysosomes did not rupture for approximately 4 hours and in fact did not release the fluorescent dye until after reaching the postmortem necrotic phase of injury. Cells treated with metabolic inhibitors also showed irreversible alterations, while lysosomes remained intact and retained the ferritin marker. The fluorochrome marker, acridine orange, escaped from lysosomes early after metabolic injury, but the significance of this observation is not clear. The results are interpreted as evidence against the concept that lysosome rupture threatens the survival of injured cells. The original suicide bag mechanism of cell damage thus is apparently not operative in the systems studied. Lysosomes appear to be relatively stable organelles which, following injury of the types studied, burst only after cell death, acting then as scavengers which help to clear cellular debris.

Production of ultrastructural membrane lesions by the fifth component of complement

A direct quantitative relationship has been demonstrated between the number of cell bound C4,2 complexes or C5 molecules and the number of ultrastructural lesions visualized on the cell membrane subsequent to immune hemolysis. When bound C4,2 complexes exceeded bound C5 molecules, the number of ultrastructural lesions seen corresponded to the number of C5 molecules. However, in the reverse situation, with bound C5 molecules in excess of bound C4,2 complexes, the latter determined the number of lesions. During the complement-reaction sequence, the lesions first became visible in the nonlytic intermediate complex EAC1,4,2,3,5 and their number was unaffected when lysis was induced by C6-C9. Since the lesions were also demonstrable on the intermediate complex EC5,6,7, it is concluded that the protein C5 is responsible for their production. Once formed, the physical presence of the C5 molecule is no longer required for the manifestation of the lesions as indicated by persistence of lesions after removal of C5 protein by trypsin. The C5-dependent ultra-structural phenomenon has therefore been interpreted to represent a true structural change of the membrane which, however, is not accompanied by a permeability defect.

In vitro reversed anaphylaxis: characteristics of anti-IgE mediated histamine release

Leucocytes from allergic and most normal human donors release histamine when challenged with antibodies against human γ-globulin. This reaction (reversed in vitro anaphylaxis) is due primarily to anti-IgE antibodies although there is some response in most donors to antisera against IgG even after it has been absorbed with light and ε chains. The anti-IgE is, however, several 100-fold more potent than the anti-IgG. By passive sensitization of the leucocytes of a normal donor with serum from a ragweed-allergic patient it was shown that the normal cells became sensitive to anti-IgE and ragweed antigen E at the same time; in both cases, there was an inverse relationship between the serum concentration used for passive sensitization and the concentration of antigen or antibody required for histamine release. There is a rough correlation (r_s = 0.42; P<0.01) between the serum IgE concentration and the response of leucocytes from allergic donors to anti-IgE and an excellent correlation (r_s = 0.82; P<0.01) between the response of the cells to ragweed antigen E and anti-IgE. There is also a strong parallel between the mechanism of direct, antigen mediated histamine release and the reversed reaction induced by anti-IgE. Both appear to be non-serum requiring, non-cytotoxic, secretory-like responses which are inhibited by theophylline, cyclic AMP and colchicine. These data suggest that cell bound IgE is of major importance in the in vitro anaphylactic response and that the direct and reversed in vitro anaphylactic reactions both operate through cell-bound IgE and share a common reaction mechanism.

Immune virolysis: effect of antibody and complement on C-type RNA virus

In the presence of envelope antibody and complement, the AKR strain of mouse leukemia virus was lysed, with the result that (i) the viral nucleic acid became susceptible to ribonuclease digestion and (ii) the internal group-specific antigen of the virus was released. The internal localization of the group-specific antigen is confirmed, the evidence being based on the failure of group-specific antibody to lyse virus in the presence of complement.