DIFFERENCES IN THE MECHANISM OF IN VITRO IMMUNE HEMOLYSIS RELATED TO ANTIBODY SPECIFICITY

Butoxyacetic acid-induced hemolysis of rat red blood cells: effect of external osmolarity and cations

Hemolysis is the principal toxicity of acute exposure to ethylene glycol monobutyl ether (EGBE) in rats. EGBE itself is not an active hemolytic agent, but its metabolite, butoxyacetic acid (BAA) formed as a result of dehydrogenase activity is a potent hemolysin. Here we address the role of osmolarity and cation composition of the suspending buffers in the mechanism of BAA-induced hemolysis of rat red blood cells in vitro. Rat erythrocytes were protected from BAA-induced cell swelling and hemolysis by the addition of sucrose to the suspending media. Hemolysis and cell swelling were also reduced by replacing external sodium with potassium. When calcium was not present in the suspending medium or when chelated by EGTA, hemolysis was increased after 2 h incubation with 1 mM or 2 mM BAA. Addition of as little as 0.05 mM CaCl(2) reduced hemolysis significantly while the addition of MgCl(2) had no effect. The dose-response relationship between BAA concentration and hemolysis determined in the presence or absence of calcium showed an increased effect of BAA in the absence of calcium. BAA-induced spherocytosis and cell fragmentation were more pronounced in the absence of calcium. The time course of BAA-induced hemolysis in the presence and absence of calcium demonstrated that the effect of calcium is to delay the onset of hemolysis. Increased intracellular calcium as a result of exposure to BAA was verified by atomic absorption spectroscopy. Charybdotoxin, an inhibitor of the calcium activated potassium channel, blocked the protective effect of calcium suggesting that the delay of onset of hemolysis in the presence of calcium is due to potassium loss caused by this channel. We conclude that the mode of action of BAA is to cause a colloid osmotic lysis of the rat red blood cell. Hemolysis requires external sodium and is associated with calcium uptake. Calcium appears to delay the onset of hemolysis. We speculate that: (1) BAA causes sodium and calcium to enter the cell; (2) calcium initially has a protective effect via the calcium activated potassium channel which facilitates the loss of potassium thereby, compensating for the osmotic effect of increased cell sodium; (3) calcium subsequently may have other deleterious effects through activation of proteases and externalization of phosphatidylserine in the exterior leaflet of the membrane.

A conserved tryptophan in pneumolysin is a determinant of the characteristics of channels formed by pneumolysin in cells and planar lipid bilayers

Pneumolysin is one of the family of thiol-activatable, cytolytic toxins. Within these toxins the amino acid sequence Trp-Glu-Trp-Trp is conserved. Mutations made in this region of pneumolysin, residues 433-436 inclusive, did not affect cell binding or the formation of toxin oligomers in the target cell membrane. However, the mutations did affect haemolysis, leakage of low-molecular-mass metabolites from Lettre cells and the induction of conductance channels across planar lipid bilayers. Of eight modified pneumolysins examined, Trp-433-->Phe showed the smallest amount of haemolysis or leakage (less than 5% of wild type). Pneumolysin-induced leakage from Lettre cells was sensitive to inhibition by bivalent cations but the extent of inhibition varied depending on the modification. Leakage by the mutant Trp-433-->Phe was least sensitive to cation inhibition. The ion-conducting channels formed across planar lipid bilayers exhibit small (less than 30 pS), medium (30 pS-1 nS) and large (more than 1 nS) conductance steps. Small- and medium-sized channels were preferentially closed by bivalent cations. In contrast with wild-type toxin, which formed predominantly small channels, the modified toxin Trp-433-->Phe formed large channels that were insensitive to cation-induced closure. Polysaccharides of molecular mass more than 15 kDa inhibited haemolysis by wild-type toxin, but polysaccharide of up to 40 kDa did not prevent haemolysis by Trp-433-->Phe. Electron microscopy revealed that Trp-433-->Phe formed oligomeric arc and ring structures with dimensions identical with those of wild-type toxin, and that the ratio of arcs to rings formed was the same for wild-type toxin and the Trp-433-->Phe variant. We conclude that the change Trp-433-->Phe affects channel formation at a point subsequent to binding to the cell membrane and the formation of oligomers, and that the size of arc and ring structures revealed by electron microscopy does not reflect the functional state of the channels.

Influence of pH and temperature on hemolysis by adult Schistosoma mansoni membranes

Membrane fractions from homogenized adult Schistosoma mansoni are known to lyse host red blood cells (RBC's), which serve as an important nutrient source for the parasite. In order to learn more about the hemolytic process, we investigated the effects of pH and temperature on the steps involved in the hemolytic process. For maximum schistosome induced hemolysis to occur the worm lytic agent must be in contact with RBCs in a low pH (pH 5.1), high temperature (37 degrees C) environment for a short time (30 min), after which hemolysis occurs at both pH 7.5 and 5.1. At pH 7.5 the hemolytic process is relatively temperature independent and highly concentration dependent. Dose-response experiments suggest that a multi-hit process of hemolysis is probably involved. Temperature and dextran experiments suggest that a pore is formed in the RBC membrane at pH 7.5. At pH 5.1 hemolysis is temperature dependent and not very concentration dependent. Dose-response data suggest that a single-hit process of hemolysis is utilized at low pH. The hemolytic process at pH 7.5, the pH of the host blood, and pH 5.1, the approximate pH of the worm gut, appears to be very different.

Complement pore genesis observed in erythrocyte membranes by fluorescence microscopic single-channel recording

The formation and opening of single complement pores could be directly observed in erythrocyte ghosts by confocal laser-scanning microscopy employing the recently introduced method of fluorescence microscopic single-channel recording. Resealed sheep erythrocyte ghosts were incubated with human complement. By limiting the concentration of C8, the eighth component of complement, the fraction of cells rendered permeable for the small polar fluorescent probe Lucifer Yellow was varied between 0.50 and 0.90. Under each condition the flux rate, k, of Lucifer Yellow was determined for a substantial number of ghosts. By analysing the sample population distribution of k the flux rate k1 of ghosts with a single pore was found to be (4.8 +/- 1.1) x 10(-3) s-1 consistent with a pore radius of about 3.5 nm (35 A). The genesis of single complement pores was studied by continuous influx measurements while triggering pore formation by a temperature shift. Pore genesis was found to be a very slow process, proceeding on a time scale of several minutes. During pore genesis the influx curves had a sigmoid shape, which excluded the possibility that the pore was preformed on the membrane surface and subsequently inserted. However, the influx curves could be well simulated by a model which assumed that pores grow stepwise by sequential incorporation of C9 monomers. The model predicts conditions under which the incorporation of single monomers can be directly revealed.

Functional size of complement and perforin pores compared by confocal laser scanning microscopy and fluorescence microphotolysis

Confocal laser scanning microscopy and fluorescence microphotolysis (also referred to as fluorescence photobleaching recovery) were employed to study the transport of hydrophilic fluorescent tracers through complement and perforin pores. By optimizing the confocal effect it was possible to determine the exclusion limit of the pores in situ, i.e. without separation of cells and tracer solution. Single-cell flux measurements by fluorescence microphotolysis yielded information on the sample population distribution of flux rates. By these means a direct comparison of complement and perforin pores was made in sheep erythrocyte membranes. In accordance with previous studies employing a variety of different techniques complement pores were found to have a functional radius of approx. 50 A when generated at high complement concentrations. The flux rate distribution indicated that pore size heterogeneity was rather small under these conditions. Perforin pores, generated in sheep erythrocyte membranes at high perforin concentrations, were found to have a functional size very similar to complement pores. Furthermore, the functional size of the perforin pore seemed to be relatively independent of the dynamic properties of the target membrane since in two cell membranes which are very different in this regard, the human erythrocyte membrane and the plasma membrane of erythroleukemic cells, the functional radius of the perforin pore was also close to 50 A. A perforin-specific antibody reduced the functional radius of perforin pores to 45 A.

Effect of osmotic protection on nucleated cell killing by C5b-9: cell death is not affected by the prevention of cell swelling

Formation of C5b-9 channels in the plasma membrane can lead to erythrocyte lysis or nucleated cell death. Lysis of erythrocytes by complement occurs as a result of colloid osmotic swelling and rupture of the plasma membrane, due to the unregulated flux of ions and water through C5b-9 channels. This colloid osmotic mechanism of lysis is largely based on the evidence that the extent of hemolysis is reduced, when macromolecules are placed in the medium to balance the osmotic gradient created by intracellular macromolecules, which are too large to diffuse through complement channels. The role of colloid osmotic deregulation, as a cause of nucleated cell killing by C5b-9, however, has been recently questioned [Kim S., Carney D. F. and Shin M. L. J. Immun. 138, 1530 (1987)]. In the present study, we investigated the effect of osmotic protection, with an 81,000 mol. wt dextran or bovine serum albumin, on Ehrlich cell killing by complement channels. The results indicated that prevention of cell swelling by dextran did not reduce the extent or rate of nucleated cell killing by either small (C5b-9l), or large (C5b-9m), complement channels when assessed by vital dye stain. The release of cytoplasmic lactate dehydrogenase as an alternative measure of cell death, however, was retarded and/or reduced, in the presence of dextran or albumin, at concns that prevented cell swelling. These results indicate that C5b-9 can kill nucleated cells effectively, in the absence of colloidal osmotic cell swelling, and that release of cytoplasmic macromolecules may not be a reliable indicator of cell death, when osmotic protectants are employed.

Comparative effects of sugars on the hemolytic activity of Schistosoma mansoni and other hemolytic agents

1. The rate of red blood cell lysis by the hemolytic agent in adult worm homogenates of Schistosoma mansoni is slowed in the presence of added sugars (50 mM). 2. Trisaccharides were the most effective in slowing and reducing lysis. Disaccharides were more effective than monosaccharides. 3. The addition of sodium, potassium or lithium chloride salts (25 mM) stimulated hemolysis by the S. mansoni agent. 4. Hemolysins with known mechanisms were tested to determine the effects of added sugars (50 mM) or salts (25 mM). 5. The S. mansoni hemolytic agent responds to the addition of sugars and salts in a manner similar to small membrane pore formers.

Schistosoma mansoni: characterization of hemolytic activity from adult worms

Homogenates of adult Schistosoma mansoni worms contain a hemolytically active component(s). Centrifugation at 10,000 g shows the major activity is present in the pellet fraction. Red blood cell lysis with the schistosome hemolytic agent is optimal at acid pH (5.0) and highly temperature dependent. The hemolytic component is resistant to boiling (5 min) and stable for extended periods of time at 38 C (22 hr). The length of the lag phase prior to hemolysis and the rate of hemolysis are both concentration and temperature dependent. Following hemolysis, red blood cell ghosts remain.

Effects of red blood cell potassium and hypertonicity on the growth of Plasmodium falciparum in culture

Malarial parasites reproduce asexually inside the erythrocytes of their vertebrate host. Relatively little is known about the interaction between host cell and parasite metabolism. In the present study the effect of host cell cation composition and osmotic shrinkage on in vitro growth and propagation of Plasmodium falciparum in human erythrocytes was investigated. It is shown that throughout the parasite cell cycle, infected cells lose potassium and gain sodium. Compartment analysis of infected cells revealed that host cell cytosol is poor in potassium and rich in sodium while in the parasite this relationship is reversed, indicating that the parasite is able to regulate its ionic composition independently. Parasites proceeded normally through their cell cycle in the presence of the sodium-pump inhibitor ouabain, although host cells lost up to 75-80% of their normal potassium content. Potassium-depleted erythrocytes harboring trophozoites and schizonts also display normal rates of protein synthesis as measured by isoleucine incorporation. Parasite growth was inhibited when infected cells were osmotically shrunken in hypertonic media, but this was not due to parasite dehydration. It is suggested that increased viscosity of host cell cytosol and/or hemoglobin gelation, are responsible for the effect, probably through interference with parasite feeding. The relevance of these results to understanding of the cellular mechanism involved in the inhibiton of parasite growth in deoxygenated sickle-trait erythrocytes is discussed.

Mechanism of membrane damage by streptolysin-O

Streptolysin-O (SLO) is a thiol-activated, membrane-damaging protein toxin of Mr 69,000 that is produced by most strains of beta-hemolytic group A streptococci. Native, primarily water-soluble toxin molecules bind to cholesterol-containing target membranes to assemble into supramolecular curved rod structures (25 to 100 nm long by ca. 7.5 nm wide), forming rings and arcs that penetrate into the apolar domain of the bilayer. Electron microscopic analyses of toxin polymers in their native and reconstituted membrane-bound form indicate that the convex surface of the rod structures is a hydrophobic, lipid-binding domain, whereas the concave surfaces appear to be hydrophilic. The embedment of the rings and arcs generates large transmembrane slits or pores of up to 30-nm diameter that can be directly visualized by negative staining and freeze-fracture electron microscopy. SLO oligomers were isolated in extensively delipidated form in detergent solution, and cholesterol was found not to detectably contribute to the observed rod structures. The rods are stable structures that resist prolonged exposure to trypsin and chymotrypsin. They can be reincorporated into cholesterol-free phosphatidylcholine liposomes to generate lesions identical to those observed on erythrocytes lysed by native SLO. Thus, although cholesterol plays a key role in the initial binding of SLO to the membrane, it does not directly participate in the formation of the membrane-penetrating toxin channels. Membrane damage by SLO is basically analogous to that mediated by previously studied channel formers, namely, the C5b-9 complement complex and staphylococcal alpha-toxin.

Correlation between toxin binding and hemolytic activity in membrane damage by staphylococcal alpha-toxin

The binding of Staphylococcus aureus alpha-toxin to rabbit and human erythrocytes was studied by hemolytic assays and sodium dodecyl sulfate-polyacrylamide gel electrophoresis immunoblotting. Hemolytic assays showed that toxin binding to 10% cell suspensions at neutral pH was very ineffective in the concentration range 3 X 10(-8) to 3 X 10(-7) M (1 to 10 micrograms/ml), and less than 5% of added toxin became cell bound. However, binding was augmented as toxin levels were raised, abruptly increasing to 50 to 60% at 2 X 10(-6) to 3 X 10(-6) M (60 to 100 micrograms/ml). When rabbit erythrocytes were lysed with 1 to 5 micrograms of toxin per ml, both monomeric and hexameric forms of the toxin could be detected on the membranes by sodium dodecyl sulfate-polyacrylamide gel electrophoresis immunoblotting. In contrast, human erythrocytes treated with 1 to 6 micrograms of toxin per ml did not lyse, and membrane-bound toxin was not detectable. When toxin concentrations were raised to 30 to 100 micrograms/ml, human erythrocytes also lysed and toxin hexamers became membrane bound in comparable amounts as on rabbit cell membranes. Lowering the pH led to a marked increase in susceptibility of human, but not rabbit erythrocytes towards alpha-toxin. When human cells were lysed at pH 5.0 with 5 micrograms of toxin per ml, membrane-bound hexameric toxin became detectable. The demonstrated correlation between the presence of hexameric, cell-bound toxin and hemolytic activity supports the channel concept of toxin-mediated cytolysis. The results also show that toxin binding does not exhibit overall characteristics of a simple receptor-ligand interaction.

Isolation and identification of two hemolytic forms of streptolysin-O

Streptolysin-O was isolated from culture supernatants of group-A beta-hemolytic streptococci (Richards strain) by ammonium sulfate and polyethylene glycol precipitation, DEAE-ion exchange chromatography, preparative isoelectric focusing, and chromatography on Sephacryl S-300. Two forms of the toxin possessing similar hemolytic capacity were identified. The native toxin was a single polypeptide chain devoid of amino sugars with a sedimentation coefficient of 3.9S and a molecular weight of 69,000, and was isoelectric at pH 6.0 to 6.4. Partial degradation of the native toxin occurred during the isolation procedure, yielding a hemolytically active polypeptide with a molecular weight of 57,000 and a pI of 7.0 to 7.5. Both forms of the toxin generated the typical, heterogeneous, open and closed ring-structured channels in erythrocyte membranes. Structural considerations indicated that between 25 and 100 monomer toxin molecules constituted the individual ultrastructurally recognizable channels. Hemolytic titrations indicated that the presence of 70 to 125 toxin molecules per erythrocyte was required to generate an average of one functional lesion per cell. The data are consistent with the concept that one or very few streptolysin-O channels will cause hemolysis.

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.

Is the membrane attack complex of complement an enzyme?

Recent studies on the functional activities of the membrane attack complex of complement, C5b-9, are reviewed. A new speculative hypothesis has been advanced to account for the ability of complement to mediate lysis of various targets. This hypothesis has three major elements: 1) that the membrane attack complex is an enzyme; 2) that the substrate for this putative enzyme is a membrane constituent; 3) that the substrate specificity of the putative enzyme is dependent on the species source of individual complement components within the C5b-9 complex.

Freeze-fracture analysis of the membrane lesion of human complement

The structure and membrane insertion of the human C5b-9(m) complex, generated by lysis of antibody-coated sheep erythrocytes with whole human serum under conditions where high numbers of classical ring-shaped lesions form, were studied in single and complementary freeze-fracture replicas prepared by unidirectional and rotary shadowing. The intramembrane portion of the C5b-9(m) cylinder was seen on EF-faces as an elevated, circular structure. In nonetched fractures it appeared as a solid stub; in etched fractures a central pit confirmed the existence of a central, water-filled pore in the molecule. Complementary replicas showed that each EF-face ring corresponded to a hole in the lipid plateau of the PF-face. Etched fractures of proteolytically stripped membranes revealed the extramembrane annulus of the C5b-9(m) cylinder on ES-faces and putative internal openings on PS-faces. Allowing for the measured thickness of deposited Pt/C, the dimensions of EF-face rings and ES-face annuli conformed to anticipations derived from negatively stained preparations. Our results support the concept that the hollow cylindrical C5b-9(m) complex penetrates into the inner leaflet of the target erythrocyte membrane bilayer, forming a stable transmembrane protein channel.

Size distribution and stability of the trans-membrane channels formed by complement complex C5b-9

We have performed double marker sieving experiments with molecules ranging from ca. 0.5-3 nm dia. in order to evaluate the size distribution of the channels formed by complement in resealed sheep erythrocyte ghosts. Evidence is presented that marker release through the channels reached equilibrium between the ghosts and the extracellular fluid in a period of 3 hr and that the channels are stable at 37 degrees C for this period of time. Under these experimental conditions we have observed a differential in the endpoint release of inositol and sucrose, which indicates that some of the ghosts carried channels measuring between 0.7 and 0.9 nm dia. No differential was observed between release of sucrose and raffinose (0.9 and 1.1 nm mol. dia., respectively). Comparisons between sucrose and inulin (0.9 and 3 nm mol. dia, respectively) showed a difference in marker release. Also, there was substantial release of inulin, indicating the presence of channels above 3 nm in dia. Hence, the present data indicate formation of channels in three size ranges, namely, 0.7-0.9 nm, 0.9-3 nm and greater than 3 nm.

Early and late events in streptolysin-O induced hemolysis

Treatment of erythrocytes with activated Streptolysin (SLO) resulted in a "swelling" of the target cells. The mean cell volume (MCV) of toxin treated human - sheep - and rabbit red blood cells increased by about 15% of the original value as measured in the Coulter Counter apparatus. Release of hemoglobin was influenced by the addition of high molecular weight colloids. In contrast ATP release was independent of the osmolarity and started before an increase in MCV was observed. The experiments indicated that "colloid osmotic lysis" is involved in SLO induced hemolysis.

The use of antibody and complement to gain access to the interior of presynaptic nerve terminals

Treatment of synaptosomes with sera containing antibodies (Ab) directed against synaptosomal membranes and complement (C) alters the plasma membrane so that it becomes selectively permeable to small molecules and ions but not to proteins. When synaptosomes are incubated with Ab and C, a rapid release of intracellular K occurs. This release does not occur after treatment with antiserum alone, or with normal serum + C. Ab + C treatment releases approximately the same amount of K as does detergent treatment or hypotonic lysis, two procedures that extensively disrupt the plasma membrane. The selectivity of the complement-induced lesion is consistent with the equivalent pore radius determined in other systems (Michaels and Mayer 1978; Sears et al. 1964). The lesions are large enough to allow the rapid permeation of small ions, but too small to permit the escape of the soluble cytoplasmic enzyme, lactate dehydrogenase. In addition, electron microscopic studies indicate that Ab + C treatment does not lead to gross morphological disruption of the synaptosomes. Ab + C treated synaptosomes are also permeable to calcium and ATP, as demonstrated by the stimulation of Ca sequestration into endoplasmic reticulum when 45Ca and ATP are added to the incubation medium.

Paroxysmal cold hemoglobinuria

The clinical and hematological features of a rare autoimmune disorder, PCH, are reviewed. Based on the case reports of 24 patients suffering from this disease, the presence of cold hemolysins in the sera of these patients as the main cause for the red cell destruction following exposure to cold is further discussed. However, recent electron microscope and biochemical studies suggest, in addition, that alterations of the red cells, and especially of their membranes, may play a role in the hemolytic process. The role of other factors, such as thermal range, specificity, and the immunological properties of the Donath-Landsteiner antibodies, as well as the role of the complement in the cold and warm phase of the Donath-Landsteiner reaction, is discussed. The differential diagnosis between PCH and the closely related CHD is outlined. While most of the reports deal with the mechanism of red cell destruction, relatively little attention is given to the treatment of the disease. It appears that the oldest remedy, i.e., warming of the patient and prevention of his exposure to cold, remains the best.

DEAE-dextran and polybrene cation inhibition of antibody/complement mediated in vitro immune haemolysis

Preincubation of unsensitized sheep erythrocytes with 25 mug/ml of the polycations DEAE-dextran or polybrene prevented immune haemolysis. This inhibition could be reversed by polyanion. When already sensitized cells were incubated in polycation or when polycation was added to complement, less effect was found on haemolysis. Cell electrophoresis and immunoelectrophoresis showed that polycation does not prevent attachment of antibody to the cells.

A membrane permeability test for the detection of cell surface antigens

A convenient microtest is described which utilizes antibody-mediated release of [14C]nicotinamide ([14C]NA) from target cells for the detection of cell surface antigens. This test is considerably more sensitive and faster than the widely used 51Cr release test because most of the [14C]NA is rapidly released from the target cells in the initial phase of membrane permeability changes induced by activated complement, as distinct from the colloid osmotic phase of complement-mediated cytolysis.

Immunological and physiological characteristics of the rapid immune hemolysis of neuraminidase-treated sheep red cells produced by fresh guinea pig serum

The rapid hemolysis by fresh guinea pig serum known to occur with neuraminidase-treated sheep red cells has been investigated with respect to the immunological and physiological properties of the lytic process. The following observations were made: (a) The susceptibility to hemolysis is directly proportional to the amounts of neuraminic acid enzymatically released from the cell surface. Complement lysis is mediated through binding of an IgM antibody protein to membranes of neuraminidase-treated cells. (b) Hemolysis is relatively temperature-independent above about 28 degrees C but below which a decrease in the hemolysis rate occurs. Arrhenius activation energies above and below the transition temperature were therefore found to be different. (c) Colloid osmotic swelling of neuraminidase-treated high potassium sheep red cells with a chloride ion concentration ratio near unity suspended in high potassium medium could not be prevented by sucrose. Hence, colloid osmotic swelling before lysis must be due to the entrance of sucrose and water since sucrose was the only external solute not at equilibrium. (d) From the rate of swelling and the apparent flux of sucrose under nonsteady state conditions an experimental permeability coefficient (P) for sucrose of 3-10(-8) cm-s-1 was computed. Comparison with a theoretical P of 4-10(-6) cm-s-1 for sucrose freely permeating through a single, hypothetical membrane lesion per cell of 60 A effective diameter indicates a membrane lesion which permits the passage of solutes larger than cations, but clearly constrains the free diffusion of sucrose.

Characteristics of streptolysin O hemolysis: kinetics of hemoglobin and 86rubidium release

The characteristics of hemolysis produced by streptolysin O (SLO) were investigated in rabbit, human, and rat erythrocytes. Kinetic studies of hemoglobin (Hb) release showed that rabbit and human erythrocytes exhibited typical "multi-hit" survival curves. Extrapolation of these curves to the ordinate indicated that approximately two molecules of SLO may be sufficient to produce lysis of a single cell. In contrast, exponential ("single-hit") survival curves were observed when rat erythrocytes were treated with SLO. At 0 C, high concentrations of SLO rapidly lysed rabbit erythrocytes; low concentrations had no effect on the cells at this temperature. The release of intracellular (86)rubidium ((86)Rb(+)) and Hb in rabbit erythrocytes exposed to SLO was investigated. In the presence of phosphate-buffered saline, rubidium and Hb were lost at the same rate from toxin-treated cells. The addition of bovine serum albumin to the suspending medium did not retard the escape of Hb, and the efflux of (86)Rb(+) only slightly preceded Hb loss. Addition of sucrose to the cells delayed both Hb and rubidium release. These results are interpreted as indicating that the "colloid-osmotic" lytic process is not involved in the hemolysis of erythrocytes by streptolysin O.

Interruption of the sequential release of small and large molecules from tumor cells by low temperature during cytolysis mediated by immune T-cells or complement

Specific lysis of tumor cells by thymus-derived lymphocytes from alloimmunized mice (T-effector specific lysis) was studied with target cells labeled with isotopes attached to both small ((14)C-labeled nicotinamide) and large ((51)Cr-labeled) molecules. The results confirm and extend previous reports that target cells release small molecules considerably earlier than large molecules during T-effector specific lysis. After interruption of T-effector specific lysis by specific antibody and complement directed against the killer cells, or by ethylenediaminetetraacetic acid, release of both isotopes continued, eventually reaching identical levels of specific release, the value of which represents the fraction of the target cell population which had been committed to die at the time these treatments were applied. On the other hand, release of both isotopes during T-effector specific lysis stops immediately when the cultures are cooled to 0 degrees . Thus, while ethylenediaminetetraacetic acid or specific complement-mediated lysis of the killer cells merely prevents the initiation of any new damage to target cells, cooling to 0 degrees also stops the lytic process in already-damaged target cells. The colloid osmotic phase of target cell lysis induced by specific antibody and complement was similarly stopped at 0 degrees in tumor cells, but not in erythrocytes. Thus, in tumor target cells, both T-effector specific lysis and complement cause a sequential release of progressively larger molecules which can be immediately stopped at any point by cooling to 0 degrees .

The fusion of erythrocytes by fatty acids, esters, retinol and alpha-tocopherol

1. The ability of a number of carboxylic acids, their esters, retinol and alpha-tocopherol to induce fusion of hen erythrocytes in vitro was investigated. 2. Some 30 different fat-soluble substances (100mug/ml) were found to cause the formation of multinucleated erythrocytes with a suspension of 3x10(8) erythrocytes/ml. The most effective agents induced fusion within 5-10min at 37 degrees C; some substances required about 1h. 3. Inclusion of Dextran 60C in the test medium minimized colloid osmotic lysis caused by exogenous lipids that induce cell fusion. 4. Cell swelling, followed by cell adhesion, was then seen to precede cell fusion. 5. Fusion occurred with C(10)-C(14) saturated carboxylic acids, with unsaturated, longer-chain carboxylic acids and their mono-esters; retinol, and to a lesser extent alpha-tocopherol, also caused cell fusion. 6. C(6)-C(9), C(15), C(16) and C(18) saturated carboxylic acids did not induce fusion within 4h; glyceryl dioleate was only weakly active, and glyceryl trioleate was inactive in the test system. 7. Fusion was facilitated by a high ratio of chemical agents to cell number and by incubation between pH5 and 6. It was inhibited by EDTA and by serum albumin. 8. Glyceryl mono-oleate caused both a similar fusion of several species of mammalian erythrocyte and the interspecific fusion of human and chicken erythrocytes. 9. The term ;fusogenic' is proposed to describe chemical, viral and physical agents that cause membranes to fuse. 10. The biochemical mechanisms involved and the possible biological significance of membrane fusion by fusogenic lipids are discussed.

Membrane lesions in immune lysis: surface rings, globule aggregates and transient openings

It is known that there are 100 A-wide circular structures associated with the erythrocyte membrane in immune lysis. To determine whether these structures were functional holes extending through the membrane, freeze-etch electron microscopy was carried out. Sheep erythrocytes incubated with either rabbit complement or rabbit antibody (anti-sheep erythrocyte antibody) did not hemolyze and did not reveal any abnormalities in freeze-etch or negative-stain electron microscopy. Erythrocytes incubated with both complement and antibody revealed rings on the extracellular surface (etch face) of the cell membrane. Allowing for the 30 A-thick Pt/C replica, the dimensions of the surface rings were similar to those seen by negative staining. The ring's central depression was level with the plane of the membrane; some rings were closed circles, others were crescent shaped. The cleavage face of the extracellular leaflet revealed globule aggregates, each aggregate appearing to be composed of about four fused globules. The cleavage face of the cytoplasmic leaflet was normal. When immune lysis was carried out in the presence of ferritin, ferritin was subsequently detected in all lysed erythrocytes. If ferritin was added after immune lysis was complete, only 15% of the cells were permeated by ferritin, indicating that transient openings exist in the cell membrane during immune lysis. No abnormal structures were detected when C6-deficient rabbit serum was used as a source of complement. It is concluded that antibody and complement produce surface rings, prelytic leakage of K(+), colloid osmotic swelling, membrane disruption, and membrane resealing; the surface rings persist after these events.

The significance of erythrocyte antigen site density. II. Hemolysis

The importance of antigen site density has been studied by means of a model passive hemolysis system using red cells coupled with sulfanilic acid groups. Relative site numbers were estimated from the covalent linkage of sulfanilic acid-(35)S to red cell membrane protein, and the effective antigen site number was determined with (125)I-labeled rabbit IgG anti-sulfanilic acid (anti-S). Immune hemolysis was demonstrated for red cells which had greater than a threshold number of antigen sites, the value of which was different for normal human cells (80,000 sites/cell), cells from a patient with paroxysmal nocturnal hemoglobinuria (PNH) (40,000 sites/cell), and sheep red blood cells (RBC) (15,000 sites/cell). Cells with antigen site densities below these values did not hemolyze when tested with 1 mg/ml purified rabbit IgM anti-S. 2-8 times greater antigen site densities were required to obtain hemolysis with IgG anti-S. Above the threshold value, hemolysis titers were proportional to the antigen site number until maximal values were obtained. The greater hemolytic efficiency of IgM antibody was demonstrated in this system, and it was established that the magnitude of the difference was related to the test cell antigen site density. These data, taken with previously reported hemagglutination studies, have been used to develop a general classification of immune hemolysis and hemagglutination based on antigen site density and antibody class. It is suggested that the heterogeneity of blood group systems is caused by differences in the site separation of erythrocyte membrane antigens.

Effect of the cationic environment on immune haemolysis of high potassium and low potassium sheep erythrocytes

Immune haemolysis was studied with the two types of genetically controlled sheep erythrocytes (E) which contain either high potassium (K) and low sodium (Na) (HK E) or low K and high Na (LK E). It was found that the susceptibility of HK and LK E to lysis by guinea-pig and human complement is influenced by the cationic environment. In veronal buffer containing 0.140 M sodium, caesium, choline or Tris, HK E were less susceptible to immune lysis than LK E. No difference was observed in potassium and in lithium(Li). Immune lysis of HK E was stimulated by the cationic series: K>Li>Rb>Cs>Na. Immune lysis of LK E was less dependent on the cationic environment, but K had a slight stimulatory effect. HK and LK E had similar reactivity with haemolytic antibody and in immune adherence. The enhancing effect of potassium was demonstrable upon E^* (an erythrocyte which has been damaged by complement but has not yet undergone lysis), suggesting that the cationic effect is produced in the final steps of immune lysis. The data suggest that the different reactivity of HK and LK E with complement in a sodium medium might be independent of the cationic permeability properties of the membrane. Inhibition of active transport by ouabain did not modify the reactivity of HK and LK E with complement in a sodium medium.