Episodic hemorrhage during honeybee venom anaphylaxis: potential mechanisms

Episodic hemorrhage is not a typical symptom of anaphylactic reaction to insect stings. Cases of reactions to honeybee (HB) sting or venom immunotherapy in which the uterus is the main target organ are very rare. Hemorrhage can be induced by HB venom components, especially melittin, which interfere with complement cleavage and bradykinin release. Both mechanisms are directly or indirectly associated with coagulation, thrombolysis, hemolysis, and smooth muscle tone. Induction of episodic hemorrhage through pathway destabilization in a defective bradykinin system or vulnerable organ may not be compensated by appropriate regulatory mechanisms. The pathological role of effectors is generally offset by the interaction of various regulatory systems, and the probability of hemorrhage is minimized thanks to this compensatory capability. In endometrial bleeding, the uterus becomes more vulnerable as a result of postmenstrual vascular fragility and additional induction of anaphylaxis-related uterine contractions. Episodic hemorrhage, especially metrorrhagia, as a consequence of HB venom activity may be suspected by an allergologist, but not by a physician. Melittin-free or recombinant allergens of HB venom, as well as modulators of the biochemical systems involved, could help to reduce the likelihood of hemorrhage. However, further investigation is required before these strategies can be introduced in clinical practice.

Gangliosides inhibit bee venom melittin cytotoxicity but not phospholipase A(2)-induced degranulation in mast cells

Sting accident by honeybee causes severe pain, inflammation and allergic reaction through IgE-mediated anaphylaxis. In addition to this hypersensitivity, an anaphylactoid reaction occurs by toxic effects even in a non-allergic person via cytolysis followed by similar clinical manifestations. Auto-injectable epinephrine might be effective for bee stings, but cannot inhibit mast cell lysis and degranulation by venom toxins. We used connective tissue type canine mast cell line (CM-MC) for finding an effective measure that might inhibit bee venom toxicity. We evaluated degranulation and cytotoxicity by measurement of β-hexosaminidase release and MTT assay. Melittin and crude bee venom induced the degranulation and cytotoxicity, which were strongly inhibited by mono-sialoganglioside (G(M1)), di-sialoganglioside (G(D1a)) and tri-sialoganglioside (G(T1b)). In contrast, honeybee venom-derived phospholipase A(2) induced the net degranulation directly without cytotoxicity, which was not inhibited by G(M1), G(D1a) and G(T1b). For analysis of distribution of Gα(q) and Gα(i) protein by western blotting, lipid rafts were isolated by using discontinuous sucrose gradient centrifuge. Melittin disrupted the localization of Gα(q) and Gα(i) at lipid raft, but gangliosides stabilized the rafts. As a result from this cell-based study, bee venom-induced anaphylactoid reaction can be explained with melittin cytotoxicity and phospholipase A(2)-induced degranulation. Taken together, gangliosides inhibit the effect of melittin such as degranulation, cytotoxicity and lipid raft disruption but not phospholipase A(2)-induced degranulation in mast cells. Our study shows a potential of gangliosides as a therapeutic tool for anaphylactoid reaction by honeybee sting.

Recognition, neutralization, and clearance of target peptides in the bloodstream of living mice by molecularly imprinted polymer nanoparticles: a plastic antibody

We report that simple, synthetic organic polymer nanoparticles (NPs) can capture and clear a target peptide toxin in the bloodstream of living mice. The protein-sized polymer nanoparticles, with a binding affinity and selectivity comparable to those of natural antibodies, were prepared by combining a functional monomer optimization strategy with molecular-imprinting nanoparticle synthesis. As a result of binding and removal of melittin by NPs in vivo, the mortality and peripheral toxic symptoms due to melittin were significantly diminished. In vivo imaging of the polymer nanoparticles (or "plastic antibodies") established that the NPs accelerate clearance of the peptide from blood and accumulate in the liver. Coupled with their biocompatibility and nontoxic characteristics, plastic antibodies offer the potential for neutralizing a wide range of biomacromolecules in vivo.

Increased sensitivity of early apoptotic cells to complement-mediated lysis

Opsonization of apoptotic cells with complement proteins contributes to their clearance by phagocytes. Little is known about the lytic effects of complement on apoptotic cells. Sensitivity of cells treated with anti-Fas antibody (Jurkat cells), staurosporine or etoposide (Raji cells) to lysis by complement was examined. As shown here, early apoptotic cells are more sensitive to lysis by antibody and complement than control cells. More complement C3 and C9 bound to apoptotic than to control cells, even though antibody binding was similar. Enhanced killing and C3/C9 deposition were blocked by benzyloxy-Val-Ala-Asp-fluoromethylketone, a pan-caspase inhibitor. Complement-mediated lysis of early apoptotic cells was also prevented by inhibitors of caspases 6, 8, 9 or 10. In contrast, caspase inhibitors had no effect on the lysis of non-apoptotic Jurkat and Raji cells. Early apoptotic Jurkat cells were also more sensitive to lysis by the pore formers streptolysin O and melittin. Sensitivity of Jurkat Bcl-2 transfectants to lysis by complement was analyzed. Enhanced Bcl-2 expression was associated with reduced C3 deposition and lower sensitivity to complement-mediated lysis. These results demonstrate that at an early stage in apoptosis, following caspase activation, cells become sensitive to necrotic-type death by complement and other pore formers. Furthermore, they suggest that Bcl-2 is actively protecting Jurkat cells from complement-mediated lysis.

Adjuvant action of melittin following intranasal immunisation with tetanus and diphtheria toxoids

Melittin, a 26-amino acid peptide and the major active component of the venom of the honey bee--Apis mellifera--has recently been shown to have absorption enhancing properties in Caco-2 cells at levels well below the level required for the generation of cytotoxicity. Given the potential of absorption enhancing agents to act as adjuvants when administered nasally [Alpar, H.O., Eyles, J.E., Williamson, E.D. and Somavarapu, S. (2001) "Intranasal vaccination against plague, tetanus and diphtheria", Adv. Drug Delivery Rev. 51, 173-201] we hypothesized that melittin may have potential as a mucosal adjuvant. Following our initial studies reported here, it was found that the co-administration of 4 microg of melittin in conjunction with tetanus toxoid in BALB/c mice was effective in eliciting markedly enhanced antibody titres in comparison to control groups and groups receiving free antigen administered intranasally. Lower concentrations of melittin were less effective and mice receiving 4 microg of melittin plus antigen exhibited antibody titres significantly higher (i.e. P<0.05) than any of the other groups tested. The observed IgG2a titres were shown to be dependent upon the dose of melittin co-administered with the immunising antigen in a similar fashion to the observed total IgG responses. In summary, melittin has been shown here to have potential as a novel mucosal adjuvant for antigens administered via the nasal route.

Lipopeptides as immunoadjuvants and immunostimulants in mucosal immunization

In previous studies we have shown that lipopeptides constitute potent immunoadjuvants in mice, rabbits and other species: in parenteral immunization, lipopeptide adjuvants were comparable, or in some cases superior to Freund's adjuvant, and were devoid of the side effects of this additive. Here we demonstrate that lipopeptides also constitute adjuvants for mucosal immunizations. The serum antibody responses against the wheat storage protein gliadin, the bee venom constituent melittin, or the hen egg protein ovalbumin could in most cases be enhanced more than 100-fold by the lipopeptide P3CSK4, applied via the nasal route. An enhanced specific antibody level could also be detected in supernatants of cell cultures prepared from spleens, Peyer's patches, lungs and mesenteric lymph nodes of immunized mice. Moreover, the lipopeptide P3CSK4 enhanced chemiluminescence in mouse spleen cells and peritoneal macrophages in vitro, indicating a macrophage-activating effect. Finally, nasal application of lipopeptide increased protection against a lethal infection of influenza. Our findings are of importance for the improvement of immunizations and might lead to more effective vaccines.

Antibody responses to bee melittin (Api m 4) and hornet antigen 5 (Dol m 5) in mice treated with the dominant T-cell epitope peptides

BACKGROUND

Mice treated with the dominant T-cell epitope peptides of allergens were reported to have reduced peptide or allergen-specific T-cell responses on subsequent immunization, but the extent of reduction of allergen-specific antibodies is not clear.

OBJECTIVE

This study was done to compare the extent of reduction of T-cell and antibody responses in peptide-treated mice. Two allergens were tested. Bee melittin (Api m 4), an allergen of 26 amino acid residues, has a single dominant T- or B-cell epitope. Hornet antigen 5 (Dol m 5), an allergen of 204 amino acid residues, has multiple dominant T- or B-cell epitopes.

METHODS

Mice were treated with T-cell peptides of Api m 4 or Dol m 5 and then immunized biweekly with their respective allergen with alum adjuvant. T-cell peptides tested were residues 7-19 of Api m 4 and residues 41-60, 141-160, and 176-195 of Dol m 5. T-cell responses at week 9 or 11 were assayed by proliferation of spleen cell cultures. Antibody responses of different isotypes were measured biweekly by ELISA.

RESULTS

Partial reduction of 30% to 50% of T-cell responses to peptide or allergen was observed in bee and hornet peptide-treated mice. About 65% reduction of Api m 4-specific antibody response was observed early in the immune response but gradually subsided to about 40% late in the response. Partial reduction of about 40% of Dol m 5-specific antibody response was only observed early in the immune response.

CONCLUSION

Peptide treatment is partially effective in the reduction of T-cell responses of univalent or multivalent allergens. It is also partially effective in the reduction of antibody response of a univalent allergen, but it is poorly effective for a multivalent allergen.

Molecular parameters in melittin immunogenicity

Based on immunogenicity studies, two T-cell epitopes in melittin were found to be functional in guinea pigs, one being centrally located, the other one residing in the C-terminal chain. In Balb/c mice only the central epitope was found to be active. A human T-cell clone was found by T-cell proliferation studies to employ strictly the C-terminal chain. Truncation of melittin peptides at the N-terminus did not markedly affect the capacity of guinea pigs to develop anti-IgG responses towards peptidic epitopes and towards a C-terminally attached haptenic group. Attachment of various substituents inside and outside the T-cell epitopic areas had no marked effect on antibody responses. In contrast, the substituents positioned within a T-cell epitope abolished T-cell proliferation. This difference between whole animal data and cellular in vitro responses is presently not understood.

Induction of an epitope-specific humoral immune response by lipopeptide-hapten conjugates: enhancement of the anti-melittin response by a synthetic T helper (Th)-cell epitope

Lipopeptides of bacterial origin constitute potent immunoadjuvants when combined with antigens. After the immunization with lipopeptides covalently coupled to non-immunogenic low-molecular-mass antigens or haptens, a hapten-specific humoral immune response can often be obtained. The response against synthetically prepared melittin fragments was further enhanced by the additional introduction of a T helper (Th)-cell epitope into the lipopeptide-hapten conjugate. The Th-cell epitope applied, which is presented by the MHC class II molecule of the BALB/c (H-2d) haplotype, consisted of a synthetic 16-amino-acid oligopeptide derived from sperm whale myoglobin. The immune-enhancing effect was most pronounced for the melittin-derived peptide fragments [Mel(1-16)] and [Mel(17-26)-CONH2]. Antibodies obtained after 3 immunizations with the conjugates recognized the synthetic as well as the native melittin molecule. Our results show that it is possible to markedly enhance a weak hapten-specific immune response by coupling the haptens to a lipopeptide conjugated to a haplotype-specific T helper-cell epitope. The novel conjugates are well suited for the optimization of immunization procedures, and for the development of novel synthetic vaccines.

Neutralization of bee venom lethality by immune serum antibodies

The lethal effects of Africanized honey bee venom depend on the absorption of venom delivered during simultaneous sting attacks by large numbers of bees. The hypothesis that antibodies to whole bee venom and bee venom components could neutralize the lethal effect of bee venom was tested. Antibodies from beekeepers and immunized rabbits were incubated with bee venom and neutralization was studied by survival of intravenously injected mice. Beekeeper serum antibodies were found effective in protecting mice challenged with whole venom, and serum from rabbits immunized with phospholipase A2 (PLA2) was effective in protection against lethal effects of PLA2. Serum antibodies from rabbits immunized with whole venom or melittin were ineffective in neutralizing whole venom in vivo and had low titers in a venom enzyme-linked immunosorbent assay. The results suggest the need for development of more effective methods for raising antitoxic antibodies to bee venom components in other animals as a means of developing an antiserum that would be effective for treatment of human victims of multiple bee stings.

Immunogenicity studies with haptenated melittin peptides: implication for membrane involvement during the recognition step

Melittin peptides carrying 2,4-dinitro-6-carboxyphenyl (Dncp) haptenic groups regularly evoked anti-hapten IgG responses in mice or guinea pigs when the hapten was C-terminally attached. Single haptens on the N-terminal helix in several positions gave poor or no responses in the early stages but adequate titres after prolonged immunization. Peptides with Dncp at the C-terminus as an invariant feature and a second Dncp in various positions along the peptide chain did not fail to produce adequate responses. The hampering effect is not due to a defect at the T-cell level but involves the recognition step on the B-cell. It is implied that the haptenic interaction with the paratope of the recognizing immunoglobulin on the B-cell involves the cell membrane in an important way. It is also suggested that late antibody responses should not be overlooked during the development of proteinaceous immunogens for vaccination.

Activation of bee venom phospholipase A2 through a peptide-enzyme complex

Phospholipase A2 activation by membrane-bound peptides was investigated in order to understand the role of the membrane-induced conformation on activation, and to examine the occurrence of a peptide-enzyme complex at the lipid/water interface. For the peptides studies, bee venom phospholipase A2 was stimulated regardless of the membrane-bound conformation (alpha-helix, beta-sheet or random coil). Using antisera raised against melittin, we were able to demonstrate the occurrence of a calcium-dependent complex involving the enzyme, phospholipid substrate, and peptide.

Immunogenicity of dinitrocarboxyphenylated melittin: the influence of C-terminal chain shortening, N-terminal substitution and prolin insertion at positions 5 and 10

Peptides derived from the bee-venom melittin were fitted with the haptenic group dinitrocarboxyphenyl (Dncp) and tested in out-bred guinea pigs for immunogenicity by measuring the IgG anti-Dncp antibody response by ELISA. Dncp-conjugates comprising virtually the entire melittin proved to be strong immunogens producing antibody responses comparable to those of proteins. Weak responses were obtained with considerably shortened sequences. Conjugates with N-terminal Dncp gave markedly reduced antibody responses compared to peptides with C-terminal Dncp. An N-terminal biotinyl substituent abolished the immune response whereas N-terminal lauryl and caprylyl had little effect. Insertion of L-proline into a hexadecapeptide conjugate abolishing the possibility of helix formation gave an immunogen to which individual animals clearly responded on a low level. Oligomerisation, but not the cytolytic activity of melittin peptides, may contribute to the immunogenicities observed.

Protein epitope mapping by mass spectrometry

A mass spectrometric method is described for the rapid mapping of linear epitopes in proteins that are bound by monoclonal antibodies. The method consists of three steps. In the first step, an antigen protein is digested by a proteolytic enzyme to produce an appropriate set of peptide fragments. In the second step, peptide fragments containing the linear epitope are selected and separated from the pool of peptide fragments by immunoprecipitation with the monoclonal antibody. In the final step, the immunoprecipitated peptides are identified by matrix-assisted laser desorption mass spectrometry. The method allows the rapid determination of antigenic sites without tedious peptide synthesis or protein mutagenesis. The approach is demonstrated through the mapping of epitopes in two peptides (melittin and glucagon-like peptide-1 7-37) against which monoclonal antibodies were raised. In addition to epitope mapping, the successful coupling between matrix-assisted laser desorption mass spectrometry and immunoprecipitation provides a potentially powerful tool for determining binding sites between proteins.

Structure-immunogenicity relationship of melittin, its transposed analogues, and D-melittin

Melittin, a 26-residue bee venom peptide, is known to induce murine Abs specific for its hydrophilic C-terminus of residues 20-26 and T cell responses specific for its hydrophobic mid-region of residue 11-19. Synthetic melittin analogues with transposed sequences of Ac(21-26) (1-20) and Ac(26-21) (1-20) are found to induce murine Abs specific for the transposed peptide segment and to induce T cell responses that are cross-reactive with melittin. Compared with melittin, the transposed melittin analogues are weaker immunogens and have lower hemolytic activities, lower helical contents, and a lower degree of association in micelles. A melittin analogue with a lactoside group at its C-terminus was found to induce lactoside-specific murine Abs. Present studies show that another analogue with a lactoside group at its N-terminus induces only Abs specific for the C-terminal region of melittin, and no lactoside-specific Abs are detected. These immunochemical observations suggest that the immunogenicity of melittin or its analogues is a consequence of its binding to cell membranes with subsequent oligomer formation in lipid bilayers. Apparently melittin or its analogues bind to cell membrane in an asymmetric manner with the exposed and the buried segments functioning as B and T cell epitopes, respectively. D-melittin is non-immunogenic in mice, although D-melittin has the same hemolytic activity as melittin. This finding may be correlated with the known resistance of D-melittin to proteolysis and hence to processing for Ag presentation to T lymphocytes.

Lipopeptide-polyoxyethylene conjugates as mitogens and adjuvants

Two lipopeptide analogues of the Escherichia coli lipoprotein rendered water-soluble by polyoxyethylene were tested for mitogenicity in vitro in murine and human B lymphocytes and for adjuvant activity in vivo in mice. These highly amphiphilic lipopeptides retained the biological activity other lipopeptides usually exerted which supports the hypothesis of specific interactions of lipopeptides with membranes of reactive cells. The activation of human B lymphocytes by these lipopeptides was much less pronounced compared to that of murine cells. However, given in combination with anti-CD40 antibodies plus interleukin-4, human B lymphocytes could synergistically be stimulated to proliferate. As an adjuvant, the polyoxyethylene linked lipopeptides were almost as potent as Freund's adjuvants and other basic lipopeptides. Being water-soluble, these novel analogues are easy to apply and they are suitable for field studies as adjuvants when sonication can not usually be provided.

Structure-immunogenicity relationship of melittin and its N-terminal truncated analogs

Melittin is an amphipathic 26-residue peptide from bee venom. We showed previously that, in the murine system, melittin has one major B-cell epitope in the hydrophilic region of residues 21-26 and one T-cell epitope in the hydrophobic midregion of 11-19. In this paper we compared the immunogenicity and the biophysical properties of a series of melittin analogs which differ by stepwise two-residue truncation in the N-terminus of residues 2-10. All analogs retain the B- and T-cell epitopes of melittin. However, the analogs which have more than two residues deleted at the N-terminus are nonimmunogenic for antibody responses although they are immunogenic for T-cell responses. The analogs were found to differ in their hemolytic activity, helical content, and oligomer formation in different solvents. These results support the hypothesis that the immunogenicity of melittin for antibody response is associated with its binding to cell membranes followed with oligomer formation but its immunogenicity for T-cell response is not.

[Comparison of anti-inflammatory, analgesic activities, anaphylactogenicity and acute toxicity between bee venom and its peptides]

Bee venom 1.0-2.0 mg/kg and bee venom peptides 1.0-2.0 mg/kg inhibited several inflammatory processes, such as ear swelling induced by xylene in mice, edema produced by injecting 1% carrageenin 0.1 ml beneath the plantar surface of hind paw in rats and showed a marked analgesic action induced by the hot plate and potassium antimony tartrate. Bee venom peptides had a markedly more effective action as compared with bee venom itself. The anaphylactogenicity of bee venom peptides was apparently milder than that of bee venom. The LD50 of bee venom ip in mice and bee venom peptides was 7.4 mg/kg and 7.9 mg/kg respectively.

Stimulus-associated protein in gastric parietal cell detected using antimelittin antibody

The bee venom polypeptide melittin binds to and inhibits the gastric hydrogen-potassium-adenosinetriphosphatase (H(+)-K(+)-ATPase). A search for parietal cell proteins with a melittin-like structure was carried out. A 67-kDa (doublet) protein, which reacted with a polyclonal antimelittin antibody, was found in purified rabbit parietal cells. The protein exhibited reversible stimulus-dependent redistribution from cytosol to (total) membranes. It was also found to be associated with H(+)-K(+)-ATPase-containing membranes when isolated from the gastric mucosae of rabbits treated with histamine, but not with cimetidine. The presence of the protein correlated with the ability of the membrane preparations to exhibit ionophore-independent HCl accumulation, a characteristic of gastric membranes from histamine-stimulated animals. The 67-kDa melittin-like protein may play a role in the functional changes in the gastric parietal cell that are involved in stimulation of HCl secretion.

Characterization of murine monoclonal antibodies to phospholipase A2 and mellitin from bee venom

9 murine monoclonal antibodies (MoAbs), 7 to phospholipase A2 (Pla2; Api m I) and two to mellitin (Api m III) have been produced. Specificities were demonstrated using immunoblotting and enzyme immunoassays (ELISA). Antibodies specific for Pla2 were characterized in detail. Epitope mapping of Pla2-specific MoAbs identified three independent binding regions. 5 selected MoAbs bound to one of these sites compete with specific human IgE. Two of MoAbs characterized are suitable tools to quantify Pla2 in a two-site binding assay.

[Determination of melittin antigenic determinants in a model membrane]

Monospecific polyclonal antibodies labelled with colloid gold were obtained against melittin in different conformations (monomer, tetramer and complex with BSA). They were used for electron analysis of the position of antigenic determinants of melittin in DMPC model membrane. The antibodies reacted in cross-immunoassay in different titres with all antigenes and this evidences for the presence of common antigenic determinants in their structures. It was found that melittin antigenic determinants in the model membrane are exposed and accessible to reaction with antibodies and, therefore, they serve the agent for stimulation of immune response and production of antibodies.

Murine IgE and IgG responses to melittin and its analogs

Melittin, a bee-venom peptide of 26 amino acids, induces IgE and IgG responses in man and animals. The antibody response was shown previously to be specific primarily for the C-terminal 6 residues and its T cell epitope in H-2d restricted mice was shown to be in residue 11-19 of melittin. To study the relationship of peptide structure and immunogenicity in mice, we have prepared a series of melittin analogs varied in length and composition at the C-terminus. Immunogenicity of the analogs for IgG and IgE responses was found to correlate with two factors: a peptide length of more than 24 residues and the presence of a hydrophilic C-terminal region preferably with two to four cationic groups. These factors result in the ability of peptide to bind to cell membranes. Analogs that possess these features are good immunogens whereas those lacking any of these features are weak immunogens.

Murine T cell responses to melittin and its analogs

The 26-residue peptide melittin from bee venom elicits high IgG1 and IgE responses in selected strains of mice. The antibody responses were shown previously to be specific mainly for the region of residue 20-26. The T cell epitope of melittin in H-2d-restricted mice is now found to be primarily in residue 11-19, corresponding to an alpha-helical amphiphilic segment of the molecule. Melittin-specific T cell lines have varying responses to different structural analogs of the melittin T cell epitope, and the results indicate that the antigenicity of T cell epitope peptides depend more on their primary structure than on their secondary structure. Melittin-specific T cell clones are found to be CD4+ and secrete IL-4, and are restricted to presentation on I-Ad or I-Ed. The I-Ad- or I-Ed-restricted clones differ in their responses to different analogs of melittin.

Human rheumatoid synovial cell stimulation by the membrane attack complex and other pore-forming toxins in vitro: the role of calcium in cell activation

The effects of non-lethal amounts of a variety of pore-forming agents on cultured human rheumatoid synovial cells (HRSC) have been investigated. Non-lethal complement membrane attack and non-lethal amounts of melittin, perforin and ionomycin all caused a biphasic release of prostaglandin E2 (PGE2) from HRSC, an early phase of release occurring within 1 hr and a second larger phase commencing after 4 hr and continuing over the 24-hr time-course. Removal of extracellular calcium abolished the release of PGE2 under all conditions of non-lethal attack. Modulation of G-protein activity reduced the second phase of release caused by non-lethal doses of the membrane-attack complex (MAC) from 800 ng/10(6) cells PGE2 to around 300 ng/10(6) cells. Non-lethal levels of the MAC also caused release of interleukin-6 (IL-6) from HRSC over the 24-hr time-course, with levels reaching 550 ng/10(6) cells at 24 hr compared to background levels of 200 ng/10(6) cells. No detectable release of IL-1 alpha could be measured at any time following non-lethal complement membrane attack. These results suggest a role for the MAC as an initiating mediator inducing the inflammation associated with rheumatoid arthritis.

Acyl carrier protein interacts with melittin

Acyl carrier protein (ACP) from Escherichia coli has been shown to form complexes with melittin, a cationic peptide from bee venom. ACP is a small (Mr 8847), acidic, Ca2(+)-binding protein, which possesses some characteristics resembling those of regulatory Ca2(+)-binding proteins including interaction with melittin. Complexing between melittin and ACP which occurred both in the presence and absence of Ca2+ was evident by chemical cross-linking the two peptides, fluorescence changes (including anisotropy measurements), and inhibition by melittin of the activity of a nonaggregated fatty acid synthetase from Euglena. Also, anti-Apis mellifera antibodies which contained antibodies against melittin specifically inhibited the same enzyme system activity relative to non-immune IgG.

Quantity, analysis, and lethality of European and Africanized honey bee venoms

Venom from Africanized honey bees (derived mainly from Apis mellifera scutellata) was compared with venom from domestic, European bees by study of lethality, immunological cross-reactivity, venom yield, isoelectric focusing (IEF) patterns, and melittin titers. The LD50s of European and Africanized bee venom by iv injection in mice were similar. In venom neutralization experiments, Africanized bee venom was mixed with antibodies from a beekeeper exposed only to European bees and used to challenge mice. Survival times of mice given these mixtures were significantly prolonged, indicating that human serum antibodies to European bee venom neutralized the lethal effects of Africanized bee venom. Reservoirs from Africanized bees contained less venom than European bees (94 and 147 micrograms venom/bee, respectively) and Africanized bee venom had a lower melittin content. The IEF patterns of venom from individual European bees varied considerably, as did IEF patterns of individual Africanized bees. Pools of venom from 1,000 bees of each population of A. mellifera showed noticeable but less obvious electrophoretic differences. The findings suggest that multiple stinging, and not increased venom potency or delivery, is the cause of serious reactions from Africanized bee attacks.

Epitope analysis: biotinylated short peptides as inhibitors of anti-peptide antibody

The interaction of anti-melittin antisera with melittin-coated ELISA plates could be inhibited by biotinylated peptides of the C terminal epitope which is one of three defined antigenic sites on the hexacosapeptide melittin. Non-biotinylated short peptides and peptide derivatives were inactive. It is suggested that biotinylation of epitopic peptides enhances their inhibitory properties in a methodologically useful way.

Identification of the discontinuous epitope in human complement protein C9 recognized by anti-melittin antibodies

Polyclonal rabbit antibodies against melittin recognize human C protein C9 and retard C9-mediated hemolysis. Human C9 contains a tetrameric and a pentameric sequence (amino acids 293-296 and 528-532, respectively) that together match a continuous segment in the melittin sequence, i.e., residues 8-16. It has been suggested that the tetrameric and the pentameric regions on C9 form a discontinuous epitope on folded C9 that mimics the structure of melittin. To further test this hypothesis, antibodies to C9-sequence-specific peptides were prepared. Peptides containing either the homologous tetrameric or the homologous pentameric sequence together with short stretches of the respective amino- and carboxyl-terminal flanking regions were synthesized, as well as a composite peptide predicted to resemble the discontinuous epitope as a linear, nine-amino acid sequence. Direct and competitive binding assays demonstrated that the tetrameric and the pentameric sequences are part of the epitope on human C9 that is recognized by anti-melittin IgG. However, only antibodies directed against the complete epitope are capable of inhibiting hemolysis. Because neither anti-tetramer nor anti-pentamer antibodies affect hemolysis whereas anti-melittin and anti-composite antibodies do, we propose that human C9 changes conformation around a hinge located between residues 296 and 528 and that the latter two antibodies inhibit unfolding required for membrane insertion and subsequent hemolysis.

Antigenic structure of the hexacosapeptide melittin: evidence for three determinants, one with a helical conformation

ELISA-based epitope analysis was performed using rabbit polyclonal antisera against melittin. Antigenic sites were found at the C-terminus, in the middle section and within the N-terminal helix. Antibodies against the helical segment could discriminate between two faces of the amphiphilic helix. The antigenic sites include the bulk of the melittin hexacosapeptide, which is synonymous with a very high epitope density.

Comparison between complement and melittin hemolysis: anti-melittin antibodies inhibit complement lysis

A comparison is made between the hemolytic actions of melittin and the ninth component of complement (C9). Melittin and C9 produce "pores" of similar effective radius in erythrocytes under standardized conditions, and their hemolytic action is suppressed by metal ions at similar concentrations, suggesting a common mechanism. Polyclonal anti-melittin immunoglobulin G (IgG) produced in rabbits retards hemolysis mediated by human C9 in a specific manner. Such antibodies react in several immunoassays with human and monkey C9 but not with C9 from lower animals, and no inhibition of lysis mediated by C9 molecules from these animals is observed. Thus, it is unlikely that anti-melittin IgG reacts with a structural element, such as an amphipathic helix, on human C9 since such structures are also predicted to exist in other C9 molecules. Human C9 and melittin block cross-reactivity in a dose-dependent manner, and anti-melittin IgG recognizes an epitope located between amino acid residues 245 and 390 of human C9 on "Western" blots. Comparison of the melittin and human C9 sequences indicates two regions of complete homology, a tetrapeptide at positions 292-295, and a pentapeptide at positions 527-531 in human C9, corresponding to residues 8-16 in melittin. Inhibition of hemolysis is not caused by blocking of C9 binding to the C5b-8 complex; rather the antibody must dissociate from the bound C9 before lysis ensues, indicating that it interferes with a postbinding event. It is proposed that anti-melittin binds to a conformational epitope on native, folded human C9 and thereby retards unfolding of the molecule, which is required for membrane insertion and hemolysis.

IgE and IgG antibody response to purified bee-venom antigens and peptides in four patients who had adverse reactions to immunotherapy

The immunological response to individual bee-venom allergens was studied in blood samples collected at frequent intervals from four bee-venom allergic patients who had suffered systemic allergic reactions to injections of bee venom during immunotherapy. All had high IgE antibody levels, at the upper end of the range found in bee-sting allergic patients, and all had antibodies to the minor allergens at the time of the reactions. These did not, however, provide a simple explanation for the reactions that occurred. We were able to observe two interesting phenomena--in one patient IgE antibodies to the individual venom antigens appeared to be 'switched off' sequentially. In another, IgE antibodies to hyaluronidase rose substantially after 4 years of therapy. We believe that these results provide evidence to support the view that the regulation of IgE antibodies is controlled by mechanisms that are both isotype- and antigen-specific.

Affinity-purified melittin antibody recognizes the calmodulin-binding domain on calmodulin target proteins

Melittin is a 26-amino acid amphipathic peptide which binds to calmodulin in a calcium-dependent manner. The utility of melittin as a peptide replica of the calmodulin-binding region of calmodulin acceptor proteins (CaMBPs) was investigated. Antibody against melittin was raised and purified by antigen affinity chromatography. Interaction of the antibody with CaMBPs was initially suggested by the ability of anti-melittin-Sepharose, but not nonimmune IgG-Sepharose, to bind calmodulin-dependent cyclic AMP phosphodiesterase. Direct interaction of melittin antibody with the calmodulin-binding domain of acceptor proteins was demonstrated by quantitative inhibition of calmodulin binding to the purified CaMBPs, myosin light chain kinase, and eel electric organ CaMBP55. These results indicate that melittin antibody identifies regions of structural similarity between calmodulin acceptor proteins, and this region includes a common calmodulin-binding domain.

A comparative study on the release of leukotrienes and histamine by guinea pig lung and trachea after challenge with antigen or stimulation with ionophore A23187 or melittin

The release of leukotrienes and histamine from guinea pig lung and trachea after immunological and nonimmunological stimulation were compared. Antigen, ionophore A23187 and melittin caused the release of leukotriene (LT)B4, LTC4, LTD4 and LTE4 from lung and trachea as determined by reverse-phase high performance liquid chromatography (RP-HPLC) and bioassay. The release of LTB4 by lung and trachea was maximum after 5 min of ionophore stimulation (128 +/- 40 and 142 +/- 29 pmol/g tissue, respectively). Lung, but not trachea, also released the 20-OH-LTB4 and 20-COOH-LTB4. The release of LTC4 by lung tissues was maximum after 5 min, whereas maximal tracheal responses occurred at 10 min (27 +/- 11 and 9 +/- 3.5 pmol/g tissue, respectively). Maximal release of LTD4 by lung and trachea respectively occurred after 10 and 15 min (103 +/- 21 and 20 +/- 6 pmol/g tissue, respectively). The release of LTD4 in response to ionophore by both tissues decreased after 15 min, whereas the release of LTE4 continued to increase. Release of leukotrienes from melittin stimulated lung was 2-3-fold less than in ionophore stimulation. In contrast, tracheal responses to melittin and ionophore for the release of LTB4 were equivalent, whereas release of peptidoleukotrienes in response to melittin was approximately 50% that resulting from ionophore. Antigen challenge was the least potent stimulus for LTB4 release in both tissues, whereas it was at least as potent as melittin for the release of peptidoleukotrienes. The release of histamine by lung tissue was approximately 2-3-fold greater than by trachea (7 +/- 1 and 2 +/- 0.5 nmol/g tissue, respectively) after 5 min of stimulation with either ionophore, melittin or antigen. These data demonstrate that lung tissues and trachea respond to immunologic stimulations by releasing the mediators of inflammation and immediate hypersensitivity. The lung releases peptidoleukotrienes and histamine 2-5-fold greater than the trachea, whereas the release of LTB4 in both tissues are approximately equal.

Melittin-specific monoclonal and polyclonal IgE and IgG1 antibodies from mice

Melittin, a bee venom peptide consisting of 26 amino acid residues, elicited high IgG and IgE antibody responses in mice of BALB/c and CAF1 strains, but not in mice of A/J, AKR, and C57BL/6 strains. Greater than 80% of the melittin-specific antibodies in sera of responder mice were found to bind the hydrophilic carboxyl-terminal heptapeptide of melittin. Three melittin-specific monoclonal antibodies were obtained from responder mice by the hybridoma technique. Two are of the IgG1 isotype and one is of the IgE isotype. One monoclonal antibody of the IgG1 isotype binds the carboxyl-terminal heptapeptide of melittin, while the other two monoclonal antibodies do not. However, competitive binding studies suggest that all three monoclonal Ig bind at the same, or adjacent, site of melittin. These findings, together with the known amphiphilic property of melittin, suggest that the immunogenicity of this peptide is a consequence of its binding to cell surface phospholipids.

Highly sensitive immunoassays based on use of liposomes without complement

We describe a novel liposome-based immunoassay in which covalently linked hapten-cytolysin conjugates are used instead of complement and surface-immobilized immunoreagents. Stable, unilamellar liposomes containing entrapped alkaline phosphatase as a marker enzyme were prepared by dialysis of octyl glucoside from suspensions of cholesterol and egg yolk lecithin. The resulting vesicles could be immediately lysed by addition of either bee venom melittin or hapten-melittin conjugates. Using ouabain, an analog of digoxin, we synthesized conjugates that were more lytic than mellitin alone but that were inhibited in the presence of antibody. This inhibition was affected by adding competing free digoxin at various concentrations to obtain standard curves. The same liposome preparations could be lysed with a biotin-melittin conjugate, which was inhibited by avidin. The latter system was affected by free biotin and might be used to couple this approach to various heterogeneous immunoassays.

Antibodies to purified bee venom proteins and peptides. I. Development of a highly specific RAST for bee venom antigens and its application to bee sting allergy

IgE antibodies to purified proteins and peptides from honeybee venom have been measured by the RAST. Trace amounts (less than 0.1%) of the major venom protein phospholipase A2 (PLA2) grossly distorted the measurement of IgE antibody to the other venom proteins, acid phosphatase (Acid P) and hyaluronidase (HYAL), and overemphasized their importance. Reduction of antigen coupled to the cellulose paper discs, which were used in the assay, diluted out the contaminating PLA2 without apparent loss in sensitivity. The reduction of disc-bound antigen increased the competition between IgE and IgG antibodies but did not affect measurement of IgE antibodies in sera taken from 35 untreated patients who had a history of general allergic reactions to bee stings. In 54% of sera from bee venom--allergic patients, the greatest IgE antibody response was to PLA2. In all, IgE antibodies to PLA2 were present in 91% of these sera. IgE antibodies to Acid P, HYAL, or melittin were present in 60%, 51%, and 31% of sera, respectively, and accounted for the highest level of binding in 17%, 17%, and 6% of these. Only 6% of sera were positive for whole venom but negative for the isolated antigens. A low level of IgE antibody was found to peptide 401 in 6% of sera. No IgE antibodies were found to apamin. While confirming the central role played by PLA2 in bee sting allergy, these results show that other venom components are also important in some patients.

Enhanced IgE and IgG anti-melittin antibody formation induced by heparin-Melittin complexes in mice

It is known that heparin which is strongly anionic will precipitate in vitro with cationic proteins such as melittin, the principal constituent of bee venom. Our experiments indicate that mice immunized with complexes of melittin and heparin produced greater amounts of IgE and IgG antibody (to this protein) than did mice immunized with melittin alone. It is possible that heparin released from mast cells following a bee sting could complex with melittin and enhance the allergenic properties of this molecule.

Antigenic, adjuvant and permeability enhancing properties of melittin in mice

Melittin, a mast cell lytic agent which comprises 50% of the protein content of bee venom, may be responsible for some of the severe reactions produced by bee stings in allergic and non-allergic individuals. We therefore investigated some of the biologic properties of this molecule in mice and found that repeated intradermal injections of melittin without adjuvant induced IgE formation in mice. In addition, melittin as well as another surfactant, saponin, were potent adjuvants for IgE formation in mice when mixed with ovalbumin (Ov). Titres of 1280 and 2560 to ovalbumin were produced in CBA mice after two injections of melittin and Ov or saponin and Ov. Melittin was also shown to have an enhancing effect on the vascular permeability induced by an antigen antibody interaction in mouse skin. Evan's blue dye was injected intravenously into ovalbumin-sensitized mice which had been injected intradermally with ovalbumin alone, melittin alone or a mixture of melittin and ovalbumin. The amount of local extravasation of dye was significantly greater in the area injected with the melittin and ovalbumin mixture than the amount of dye obtained from the skin site injected with melittin alone plus that extracted from the site injected with ovalbumin alone.

Immunological studies on bee-keepers: specific IgG and subclass typing IgG against bee venom and bee venom components

Specific IgE antibodies against bee venom and its components were studied in 23 bee-keepers. The highest IgG serum levels were observed for whole bee venom followed by phospholipase A. The serum levels of specific IgG antibodies against melittin and MCD-peptide were lower, the lowest serum levels being observed for apamin. After a 5 month absence from bee-keeping a fall in the serum levels of IgG antibodies was observed in all the bee-keepers studied. The investigation of the IgG subclass antibodies 1-4 against bee venom and phospholipase A demonstrated the highest serum levels for IgG 4 and IgG 2, the lowest levels were observed for IgG 1. The lowest IgG serum levels were associated with the least effective protection to bee stings. These findings support the concept that specific IgG antibodies prevent the development of allergic symptoms after bee sting.

IgE antibodies to bee venom, phospholipase A, melittin and wasp venom

Specific IgE antibodies against bee venom, phospholipase A, melittin and wasp venom have been examined in fifty patients with an unusually severe reaction after bee or wasp sting. Two thirds of the bee venom-sensitive patients also have detectable IgE antibodies to wasp venom. More than 50% of the wasp venom-sensitive patients are also allergic to bee venom. Phospholipase A and melittin IgE antibodies were found, respectively, in two thirds and one third of the bee venom-sensitive cases. Specific IgE antibody determinations by the Radioallergosorbent test play an essential role in the diagnostic work. After a reaction to hymenoptera stings both bee and wasp venom tests are necessary due to the high incidence of a false or incomplete identification of the stinging insect. Melittin, known for its potent pharmacological activity and possibly responsible for most of the side effects in bee venom immunotherapy, can probably not be excluded from therapeutic venom preparations since IgE antibodies to the melittin preparation were detected in one third of the cases.

Honey bee venom allergy immunological studies of systemic and large local reactions

The IgE and IgG antibody responses to four allergen fractions of honey bee venom were studied in 13 sera from patients who experienced systemic reactions from bee stings and eight from those who experienced large locals. Both groups were similar in allergen response. IgE and IgG levels and ratios. A significant number of patients were found to have experienced both types of reactions from bee stings. It is proposed that IgE antibody positive systemic and large local reactions are both IgE mediated allergic reactions. The determining factors for reaction type include venom dose and sting site.

Melittin: an allergen of honeybee venom

The presence of serum IgE antibodies to melittin was tested by the radioallergosorbent test (RAST). Melittin, the principal protein of honeybee venom, was isolated by gel filtration on Sephadex G-75 and covalently bound to cyanogen bromide-activated microcrystalline cellulose. The melittin preparation was homogenous by immunoelectrophoresis with the use of rabbit antiserum to whole honeybee venom and by polyacrylamide electrophoresis in gels containing 1% sodium dodecyl sulfate. Elevated serum IgE antibodies to melittin (three times greater than binding by normal sera) were found in 7 of 24 honeybee venom-sensitive persons and in 5 of 20 nonsensitive beekeepers. In one venom-sensitive patient a particularly high titer of IgE antibody was found. The reaction between solid-phase melittin and IgE antibody could be inhibited by fluid-phase melittin but not by phospholipase A (PLA). Similarly, the reaction of IgE antibody with solid-phase PLA was inhibited by PLA but not by melittin. In passive transfer skin tests with the sensitive patient's serum, positive wheal-and-flare reactions were obtained in 3 nonallergic recipients following melittin challenge; appropriate controls were negative. These results indicate that melittin is an allergen in some honeybee venom-sensitive patients and in an occasional patient melittin may be a major allergen.