Studies on the mast cell triggering action of certain artificial histamine liberators

The use of synthetic peptides in the delineation of immunoglobulin antigenic epitopes and Fc effector functions

As an alternative strategy to the use of proteolytic and chemical cleavage in the production of fragments of immunoglobulins retaining Fc effector functions, peptides representative of amino acid sequences constituting the putative active sites have been synthesized and assessed for biological activity in various in vitro systems. This approach has been adopted in attempts to define more precisely the autoantigenic epitope on human IgG against which anti-gamma-globulin antibodies (the so-called general 'rheumatoid factors'), found in the sera and joint fluids of patients with rheumatoid arthritis, are directed. Synthetic peptides representative of epsilon-chain sequences are being used in the production of antibodies (polyclonal and monoclonal) directed against specific epitopes within the Fc regions of human and rat IgE. The ability of these antisera to influence the in vitro functional properties of IgE anaphylactic antibodies is now under investigation, with particular attention being focused on cytophilicity and mast cell triggering. Preliminary findings suggest that certain of the antisera might be capable of inhibiting mast cell sensitization by IgE antibodies, and therefore might form the basis of a new type of anti-allergy compound.

G protein activation: a receptor-independent mode of action for cationic amphiphilic neuropeptides and venom peptides

The neuropeptide substance P, the venom peptide mastoparan and the synthetic polyamine compound 48/80 activate rat peritoneal mast cells, leading to rapid histamine release by exocytosis. Although these effects are inhibited by pertussis toxin and involve a transient increase in IP3, no selective membrane receptors have been identified. However, it has recently been shown that these compounds activate G proteins in vitro. Here Yves Landry and colleagues discuss the proposal that direct activation of G protein is the physiological mechanism of action of substance P on rat peritoneal mast cells, this mechanism being mimicked by mastoparan and 48/80, and possibly by other cationic amphiphilic peptides such as kinins. These compounds might be of help in defining the interaction between membrane receptors and G proteins.

The role of non-antigen receptors in mast cell signalling processes

Cytophilic antibodies of the IgE class play two distinctive roles in the immunological triggering of mast cell, initially by binding to Fc receptors on the plasma membrane and secondly, by transmitting to the sensitised target cell the effects of their subsequent interaction with specific antigen (allergen). In contrast to the claim that the IgE antibody merely acts as a surrogate receptor in its latter role, evidence is presented in support of the contention that it is actively involved in mast cell triggering by providing a signal to a second "receptor" [i.e. other than Fc(epsilon)R]. Synthetic peptide studies have provided an insight into the structural characteristics of such an Fc effector site, besides beginning to suggest the manner of its interaction with the mast cell membrane. In discussing the implication of our findings, this type of immunological trigger process is contrasted with that brought about by hormone agonists. It is suggested that the cytophilic IgE antibody can be regarded as a pro-hormone, which only gains hormonal status as a result of cross-linking by specific antigen.

The capacity of basic peptides to trigger exocytosis from mast cells correlates with their capacity to immobilize band 3 proteins in erythrocyte membranes

The effect of mast-cell-triggering peptides on the rotational properties of band 3, a protein component of the human erythrocyte membrane, was measured by observing flash-induced transient dichroism of the triplet probe eosin maleimide. In the presence of melittin, polylysine and five synthetic peptides, varying degrees of retardation in the rotational motion of band 3 were produced. When placed in order of band 3 immobilizing activity, the peptides formed a series identical with their order of efficacy in releasing 5-hydroxytryptamine from rat peritoneal mast cells. The correspondence in the abilities to immobilize band 3 in the erythrocyte and trigger mast cells is significant because structure-activity analyses of the peptides show both processes to have the same cationic, hydrophobic and stereochemical requirements. Probably, the immobilization of band 3 proteins reflects an ability of the basic peptides to aggregate anionic surface moieties, and therefore a similar mechanism is implied in mast-cell triggering.

Essential structural requirements for triggering of mast cells by a synthetic peptide comprising a sequence in the C epsilon 4 domain of human IgE

A range of synthetic analogues of the peptides Lys-Thr-Lys-Gly-Ser-Gly-Phe-Phe-Val-PheNH2 (human IgE epsilon-chain 497-506 decapeptide) and Lys-Thr-Lys-Gly-Ser-Gly-Phe-PheNH2 (epsilon-chain 497-504 octapeptide) were tested for activity as releasers of 5-hydroxytryptamine from rat peritoneal mast cells. The following structural modifications were found to abrogate activity: N-acetylation of the alpha-amino group of the N-terminal lysine residue; substitution of the two lysine residues by either serine or glutamine; depletion of the two C-terminal hydrophobic residues (Val-Phe) of the decapeptide; and substitution of phenylalanine by alanine in the C-terminal position of the octapeptide. These observations point to a requirement for positively charged amino acids and hydrophobic amino acids at the N- and C-terminus respectively for triggering of mast cells by these short-chain peptides. Releasing activity was also found to depend on the stereospecific conformation of the positively charged region, since substitution of L-isomeric amino acids by D-isomeric forms in the three N-terminal positions of the decapeptide led to loss of potency. Inactive analogues of the decapeptide and octapeptide, at concns up to 10(-4) M, failed to antagonise the mediator-releasing effects of the active decapeptide at concns of 3 X 10(-6) - 10(-4) M.

The hexa- and pentapeptide extension of proalbumin: lack of peptide-induced histamine-releasing activity by this hexapeptide in rat mast cells and human leucocytes

It is well documented that small basic peptides with lipophilic counterparts induce non-cytolytic histamine release particularly from rat peritoneal mast cells, and to a lesser extent from human leukocytes. Since pro-albumin hexapeptide with its lipophilic core also exhibits a high percentage of basic amino acid residues, it was thought valid to investigate its potential histamine releasing activity using the above-mentioned cell systems. Results show that the peptide failed in both cell types to induce histamine release, or to inhibit IgE mediated or anaphylatoxin induced histamine release up to concentrations of 10(-4) M.

Effect of disodium cromoglycate and cyclic AMP-active drugs on cytotoxic histamine release from rat mast cells

Disodium cromoglycate and compounds which elevated levels of cyclic AMP in the mast cell variously inhibited cytotoxic histamine release induced by the surface active agents melittin, Tween 20 and Triton X-100. These results are inconsistent with the postulated effects of the drugs on receptor mediated calcium channels and alternative explanations of their action are considered.

Immunoglobulin E decapeptide-induced 5-hydroxytryptamine release from rat peritoneal mast cells. Comparison with corticotropin-(1-24)-peptide, polyarginine, polylysine and antigen

A synthetic basic decapeptide from the C4 domain of human immunoglobulin E, corticotropin-(1-24)-peptide, polyarginine and polylysine stimulated up to 90% net release of 5-hydroxytryptamine from mast cells in rat peritoneal-cell suspensions. Concentration-response curves to all four polypeptides were parallel. Polyarginine and polylysine (EC50 congruent to 0.05 microM) were approximately 100-fold more potent than immunoglobulin E decapeptide and corticotropin-(1-24)-peptide (EC50 congruent to 5 microM). Polypeptide-induced release was complete within 5-10s. Immunoglobulin-E-decapeptide-induced 5-hydroxytryptamine release was additive to that induced by low concentrations of polyarginine, but non-additive to that induced by high concentrations of polyarginine. In contrast, release induced by antigen was additive along the whole length of the concentration-response curve to polyarginine. Benzalkonium chloride inhibited immunoglobulin-E-decapeptide- and polyarginine-induced 5-hydroxytryptamine release but enhanced release induced by immunological stimulation.

Further studies on histamine release from rat mast cells in vitro induced by peptides. Characteristics of a synthetic intermediate with potent releasing activity

Previous studies on histamine release by corticotropin peptides and melittin peptides were extended, leading to the identification of a synthetic peptide intermediate, Lys(Z)-Arg(NO2)-Arg(NO2)OMe, (I) as an active non-cytolytic histamine releaser from rat mast cells. However, significant differences in the releasing capacity of optical isomers of this compound, and of Lys-Lys-Arg-ArgOMe [methyl ester of corticotropin-(15-18)-tetrapeptide; 'basic core'] were observed, with the L-forms being markedly more active. A study of various analogues of the tripeptide compound (I) indicated that the structural basis for mast-cell triggering by such peptidic agents was highly specific. The relevance of these observations to the immunologically induced histamine-release processes is discussed.

Synthetic peptides comprising sequences of the human immunoglobulin E heavy chain capable of releasing histamine

On the basis of previous studies on the structure-activity relationship of model polypeptide histamine liberators, a site within the Fc region of immunoglobulin E antibody molecules has been proposed as that responsible for the direct triggering of target mast cells after antigen challenge. Peptides comprising this region of the epsilon-chain have now been synthesized and shown to induce histamine release from normal rat peritoneal mast cells in a selective manner essentially similar to that mediated by anaphylactic antibody-antigen interaction.

Honey bee venom melittin: correlation of nonspecific inflammatory activities with amino acid sequences

The nonspecific (nonallergic) inflammatory activity of melittin, a protein toxin from honeybees, was correlated with specific amino acid sequences. Two different amino acid sequences of melittin were found to contribute to nonspecific inflammatory activities in guinea pig skin. Carboxy terminal peptide sequences of 7--10 amino acids induced immediate inflammatory reactions that reached maximum intensities by 15--30 min, then rapidly dissipated. The amino (N) terminal hydrophobic sequence, although not directly inflammatory, intensified the immediate reaction, causing a severe lesion evident by 2 h and characterized by massive polymorphonuclear leukocyte infiltration. A conceptual model of bee venom-induced inflammation in nonallergic individuals is suggested.