ABSTRACT
Aim evaluation of specific T-cell immunity against SARS-CoV-2 in primary and secondary response to virus antigens by screening method. MATERIALS AND METHODS: Patients were tested 11.5 months after COVID-19 and 610 months before and after vaccination. Healthy volunteers were screened before, 26 times during the vaccination course, and 68 months after revaccination with the Sputnik V vaccine. IgG and IgM antibodies to SARS-CoV-2 were detected by ELISA using commercially available kits (Vector-Best, Russia). Antigenic (AG) activation of T cells in the fraction of bloods mononuclear cells was assessed by IFN- production after AG stimulation in the wells of plates from ELISA kits intended for detection of antibodies against SARS-CoV-2. Data were processed by MS Excel and Statistica 10.0 software. RESULTS: AG-specific T cells were detected in 88.5% of vaccinated healthy volunteers, half of whom were found to have T cells appearing earlier than antibodies to AG. After 6-8 months, the level of AG activation decreases. Following the revaccination, the level of AG activation of memory T cells in vitro increases within six months in 76.9100.0% of vaccinated subjects. On the contrary, after COVID-19, 86.7% of individuals had in their blood the AG-specific T cells with high activity at the time of vaccination. The activity of T cells recognizing the RBD domain of the SARS-CoV-2 S protein and the proportion of individuals who had these cells in their blood increased after the vaccination of reconvalescents. CONCLUSION: T-cell immunity against SARS-CoV-2 antigens has been shown to persist for 6 months after illness. In vaccinated individuals without history of COVID-19, such duration of the preservation of AG-specific T cells in blood was only achieved after the revaccination.
Subject(s)
COVID-19 , T-Lymphocytes , Humans , COVID-19/prevention & control , SARS-CoV-2 , Vaccination , Antibodies, ViralABSTRACT
INTRODUCTION: The development of the COVID-19 pandemic has stimulated the scientific research aimed at studying of the mechanisms of formation the immunity against SARS-CoV-2. Currently, there is a need to develop a domestic simple and cost-effective specific method suitable for monitoring of T-cell response against SARS-CoV-2 in reconvalescents and vaccinated individuals. AIM: Development of a screening method for evaluation specific T-cell immunity against SARS-CoV-2. MATERIALS AND METHODS: Total 40 individuals who had mild to moderate COVID-19 and 20 healthy volunteers who did not have a history of this disease were examined. The presence and levels of IgG and IgM antibodies to SARS-CoV-2 were identified in participants sera by ELISA using the diagnostic kits from JSC Vector-Best (Novosibirsk, Russian Federation). Antigenic stimulation of mononuclear cells was carried out on commercial plates with adsorbed whole-virion inactivated SARS-CoV-2 antigen (State Research Center of Virology and Biotechnology VECTOR Novosibirsk, Russian Federation). The concentration of IFN- was measured in ELISA using the test systems from JSC Vector-Best (Novosibirsk, Russian Federation). The immunophenotyping of lymphocytes was performed on a flow cytometer Cytomics FC500 (Beckman Coulter, USA). Statistical data processing was carried out using the Microsoft Excel and STATISTICA 10 software package. RESULTS: Stimulation of mononuclear cells isolated from the peripheral blood with whole-virion inactivated SARS-CoV-2 antigen fixed at the bottom of the wells of a polystyrene plate showed a significantly higher median response in terms of IFN- production in 40 people who had history of COVID-19 compared to 20 healthy blood donors (172.1 [34.3575.1] pg/ml versus 15.4 [6.925.8] pg/ml, p 0.0001). There was no difference in median IFN- levels in supernatants collected from unstimulated mononuclear cells from COVID-19 reconvalescents and healthy donors (2.7 [0.411.4] pg/ml versus 0.8 [0.023.3] pg/ml, p 0.05). The overall sensitivity and specificity of this method were 73% (95% CI 5888%) and 100% (95% CI 100100%), respectively, at a cut-off of 50 pg/ml. CONCLUSION: The developed method for assessment of the cellular immune response to SARS-CoV-2 can be used as a screening method for monitoring the T-cell response in a population against a new coronavirus infection in recovered people.
Subject(s)
COVID-19 , SARS-CoV-2 , Humans , COVID-19/diagnosis , COVID-19/epidemiology , Pandemics , T-Lymphocytes , Enzyme-Linked Immunosorbent Assay , Antibodies, ViralABSTRACT
The aim of the study was to develop some approaches to evaluate the basic parameters of the humoral and cellular immune response to a bacteriophage, taking into account the multifactorial aspects of its interaction with both the pathogen and the macroorganism. The necessary reagents were obtained and a line of diagnostic ELISA test systems was designed to allow semi-quantitative assessment of the anti-bacteriophage IgG-antibody level in serum or other biological human fluids, as well as in preparations obtained from human blood. The need for neutralization reaction to determine the effect of detected antibodies on phage activity against a target bacterium has been proven. Testing the approaches used in the investigation of patients' blood sera showed that antibodies to bacteriophages synthesized during phage therapy are not always neutralizing. Also approaches have been developed to evaluate cell immunity reactions to bacteriophage namely to identify T-lymphocytes (T-helpers and cytotoxic lymphocytes) that can be activated in the presence of the phage under study (by expressing the early activation marker (CD69) and by the ability to produce IFNγ). Approbation of the technique in the study of lymphcytes in patients during phage therapy showed the presence of activated cells by both the CD69 expression and IFNγ production, the dynamics of which depended on the timing and frequency of therapy. The appearance of neutralizing anti-phage antibodies and corresponding activated T-lymphocytes should be taken into account in phage therapy, the effectiveness of which can directly depend not only on the activity of the phage against the target bacterium, but also on the response of the patient's immune system to the bacteriophage.
Subject(s)
Antibodies, Viral/blood , Bacteriophages/immunology , Immunity, Cellular , Immunity, Humoral , Antibodies , Antibodies, Neutralizing/blood , Antigens, CD , Antigens, Differentiation, T-Lymphocyte , Enzyme-Linked Immunosorbent Assay , Humans , Immunoglobulin G/blood , Interferon-gamma , Lectins, C-Type , Lymphocytes , Phage Therapy , T-Lymphocytes/immunologyABSTRACT
This study examined the blocking action of the selective channel blocker of calcium-permeable (CP) AMPA receptors, N1-(1-phenylcyclohexyl)pentane-1,5-diaminium bromide (IEM-1925), on excitatory postsynaptic currents in rat neostriatal and cortical neurons and in fly neuromuscular junctions. In both preparations, the blocking of CP-AMPA receptor currents increased along with the stimulation frequency. The continuous presence of kainate, which activates AMPA receptors, in the external solution also caused an enhanced blocking effect. Likewise, decrease of the synaptic release by lowering calcium concentration resulted in significant reduction of the blocking action. The activity dependence of the block is explained using the guarded receptor model. The drug molecule can only bind if the channel is open. After the channel has closed, the drug molecule remains trapped inside. However, the trapped molecule slowly egresses from closed channels to the cytoplasm. The total block effect is determined by the equilibrium between accumulation of the drug in the open channels and relief from the closed channels. Therefore, the conditions that favour the open state result in enhanced inhibition. This significant finding reveals a new way to modulate CP-AMPAR-mediated transmission using a physiologically relevant approach. Moreover, it allows the involvement of CP-AMPARs in the physiological and pathological processes such as high-frequency synaptic activity or increase of the steady-state glutamate concentration to be examined.
Subject(s)
Calcium/metabolism , Diamines/pharmacology , Quaternary Ammonium Compounds/pharmacology , Receptors, AMPA/antagonists & inhibitors , Animals , Brain/drug effects , Brain/metabolism , Diptera/metabolism , Electric Stimulation , Excitatory Postsynaptic Potentials/drug effects , Glutamic Acid/metabolism , In Vitro Techniques , Interneurons/drug effects , Interneurons/metabolism , Kinetics , Male , Models, Neurological , Neuromuscular Junction/drug effects , Neuromuscular Junction/metabolism , Rats , Rats, Wistar , Receptors, AMPA/metabolism , Synaptic Transmission/drug effectsABSTRACT
Pharmacological properties of ionotropic glutamate receptors from Calliphora vicina larvae neuro-muscular junction (C. vicina iGlurs) were studied by two-electrode voltage-clamp technique. Characteristics of the ion channel pore were analyzed using a 26-member series of channel blockers, which includes mono- and dicationic derivatives of adamantane and phenylcyclohexyl. Structure-activity relationships were found to be markedly similar to the Ca2+-permeable AMPA receptors (AMPAR) but not NMDA receptors (NMDAR) channel subtype seen in vertebrates. Like AMPARs the channels of C. vicina iGlurs are sensitive mainly to dicationic compounds with 6-7 spacers between hydrophobic headgroup and terminal aminogroup. Study of the voltage dependence of block demonstrated that, like AMPARs, the C. vicina iGlur channels, are permeable to organic cations with dimensions exceeding 10 A. Concentration dependence of block suggests the presence of two distinct channel populations with approximately 20-fold different sensitivity to cationic blockers. The recognition domain properties are more complex. Besides glutamate, the channels can be activated by kainate, quisqualate and domoate. Competitive antagonists of AMPAR and NMDAR are virtually inactive against the C. vicina iGlurs as well as allosteric modulators GYKI 52466 and PEPA. Surprisingly, the responses were potentiated 3 times by 100 mkM of cyclothiazide. We conclude that the channel-forming domain of C. vicina iGlurs is AMPAR-like, whereas the recognition domain is specific.
Subject(s)
Diptera/metabolism , Insect Proteins/metabolism , Neuromuscular Junction/metabolism , Receptors, AMPA/metabolism , Animals , Binding Sites , Dose-Response Relationship, Drug , Excitatory Amino Acid Antagonists/chemistry , Excitatory Amino Acid Antagonists/metabolism , Excitatory Amino Acid Antagonists/pharmacology , Excitatory Postsynaptic Potentials , Insect Proteins/antagonists & inhibitors , Insect Proteins/chemistry , Larva/metabolism , Molecular Conformation , Neuromuscular Junction/drug effects , Neuromuscular Junction/embryology , Patch-Clamp Techniques , Protein Structure, Tertiary , Receptors, AMPA/antagonists & inhibitors , Receptors, AMPA/chemistry , Receptors, N-Methyl-D-Aspartate/metabolism , Structure-Activity RelationshipABSTRACT
In experiments on the nerve-muscle junction of the fly larva Calliphora vicina, regularities of the blocking action of organic cations on ion channels of glutamate postsynaptic receptors have been studied. In total, 26 compounds were studied. The following regularities of structural-functional relations have been revealed: 1) the channels are not blocked by monocation compounds; 2) bication derivatives block efficiently the channel with a certain distance between hydrophobic group and terminal amino group; 3) bication compounds with trimethylammonium terminal group are significantly more efficient than compounds with non-substituted amino group. All these regularities are characteristic of blockade of the AMPA channels, but not of the vertebrate type NMDA channels. Earlier it has been shown that differences in structural-functional relations during blockade of the AMPA and NMDA channels are determined by different location of the hydrophobic and hydrophilic components of the binding area as well as by different diameter of the channels. The fact that channels of the fly larva receptor demonstrate the same regularities of blockade as the vertebrate AMPA channels indicates their structural similarity that is a consequence of their high homology.
Subject(s)
Diptera/metabolism , Insect Proteins/metabolism , Ion Channels/metabolism , Receptors, AMPA/metabolism , Receptors, N-Methyl-D-Aspartate/metabolism , Animals , Diptera/chemistry , Hydrophobic and Hydrophilic Interactions , Insect Proteins/antagonists & inhibitors , Insect Proteins/chemistry , Ion Channels/antagonists & inhibitors , Ion Channels/chemistry , Larva/chemistry , Larva/metabolism , Neurotransmitter Agents/pharmacology , Protein Structure, Tertiary , Receptors, AMPA/antagonists & inhibitors , Receptors, AMPA/chemistry , Receptors, N-Methyl-D-Aspartate/antagonists & inhibitors , Receptors, N-Methyl-D-Aspartate/chemistry , Structural Homology, Protein , Structure-Activity Relationship , Vertebrates/metabolismABSTRACT
A complex study of the effects of Acilact on the immune and interferon status, phagocyte defense, and cytokine balance in sickly children showed that Acilact had a positive effect on the immune system in these patients. The preparation is able to normalize abnormal immune parameters, and does not influence healthy immune system. In some ways Acilact has advantages over IRS 19 vaccine. Simultaneous administration of these two preparations is appropriate in some cases.
Subject(s)
Biological Products/pharmacology , Biological Products/therapeutic use , Health Status , Antigens, CD/drug effects , Antigens, CD/immunology , Bacterial Vaccines/pharmacology , Bacterial Vaccines/therapeutic use , Child , Child, Preschool , Ecology , Humans , Lactobacillus acidophilus , Probiotics/therapeutic use , Respiratory Tract Infections/epidemiology , Respiratory Tract Infections/prevention & controlABSTRACT
The effects of adenosine and ATP were studied on blowfly larvae Calliphora vicina neuromuscular preparation. Adenosine diminished (IC50 = 40 +/- 3 microM) the amplitude of nerve-evoked postsynaptic currents (EPSCs) and slightly decreased the frequency of spontaneous currents without affecting their amplitude. EPSCs were slightly reduced by ATP, and this effect was prevented by concanavalin A. Presynaptic inhibition by adenosine was temperature-dependent and insensitive to pertussis toxin. A1 agonists of vertebrate adenosine receptor CPA and NECA failed to reproduce the effect of adenosine, and 2-CADO enhanced the EPSCs. A1 antagonist DPCPX competitively inhibited adenosine action. A2 agonist DPMA potentiated EPSCs, and its effect was abolished by A2 antagonist DMPX. Adenosine and ATP failed to affect the nonquantal release of glutamate. The results show for the first time the presence of presynaptic adenosine receptors regulating transmitter release at insect motor nerve terminals and point to differences in pharmacological properties of adenosine receptor subtypes in insects and vertebrates.
Subject(s)
Diptera/physiology , Motor Neurons/physiology , Nerve Endings/physiology , Receptors, Purinergic P1/physiology , Adenosine/pharmacology , Adenosine Triphosphate/pharmacology , Animals , Excitatory Postsynaptic Potentials/drug effects , Glutamic Acid/metabolism , In Vitro Techniques , Larva/physiology , Neural Inhibition , Neuromuscular Junction/physiology , Pertussis Toxin/pharmacology , Presynaptic Terminals/drug effects , Presynaptic Terminals/physiology , Purinergic P1 Receptor Agonists , Purinergic P1 Receptor Antagonists , Receptors, Purinergic P1/metabolism , TemperatureABSTRACT
The channels of four types of ionotropic glutamate receptor (NMDA receptors and Ca-permeable AMPA receptors of rat brain neurons, and cation-selective receptors from mollusk neurons and insect postsynaptic muscle membranes) and two subtypes of nicotinic cholinoreceptor (from frog neuromuscular junctions and cat sympathetic ganglia) were studied. The structural characteristics of channels determining their susceptibility to blockade by organic mono- and dications were identified. These studies used homologous series of adamantane and phenylcyclohexyl derivatives. These experiments showed that the receptors studied here could be divided into two groups. The first group included the AMPA receptor and the mollusk and insect receptors. These were characterized by the lack of effect on the part of monocations and a strong relationship between the activity of dications and the distance between nitrogen atoms. The second group included the NMDA receptor and both subtypes of the nicotinic cholinoreceptor (muscular and neuronal). Here, conversely, the activity of monocations and dications, regardless of their lengths, were essentially identical. A model for the binding sites of blockers in channels is proposed, which takes these observations into account.
Subject(s)
Excitatory Amino Acid Antagonists/pharmacology , Receptors, Glutamate/chemistry , Animals , Brain Chemistry/drug effects , Cations/pharmacology , Cats , Diptera/physiology , Excitatory Postsynaptic Potentials/drug effects , Ganglia, Invertebrate/drug effects , In Vitro Techniques , Mollusca/physiology , Neuromuscular Junction/drug effects , Rana temporaria , Rats , Rats, Wistar , Receptors, AMPA/chemistry , Receptors, AMPA/drug effects , Receptors, Glutamate/drug effects , Receptors, N-Methyl-D-Aspartate/chemistry , Receptors, N-Methyl-D-Aspartate/drug effects , Sympathetic Nervous System/drug effects , Synaptic Transmission/drug effectsABSTRACT
Experimental results have demonstrated a significant decrease in the level of alcohol consumption by albino rats immunized with heterologous horse alcohol dehydrogenase. The role of ADH epitopes 9-14, 93-115, and 265-276 in this phenomenon was examined, and it was established that the latter sequence (265-276) plays the biggest role. The inhibition of ADH activity in the adrenals of immunized rats was much higher compared to the liver. We propose a hypothesis that the effect of alcohol dehydrogenase on alcohol consumption is connected with its role in catecholamine metabolism.
Subject(s)
Adrenal Glands/immunology , Alcohol Dehydrogenase/immunology , Alcohol Drinking/immunology , Adrenal Glands/enzymology , Alcohol Drinking/prevention & control , Animals , Enzyme Activation/immunology , Epitopes/immunology , Immunization , Male , Rats , Rats, WistarABSTRACT
The topography of the channel binding site in glutamate receptors (AMPA and NMDA types of rat brain neurons, receptors of molluscan neurons and insect muscle), and in two subtypes of nicotinic cholinoreceptors (in frog muscle and cat sympathetic ganglion), has been investigated by comparison of the blocking effects of mono- and dicationic derivatives of adamantane and phenylcyclohexyl. The channels studied can be divided into two groups. The first one includes AMPA receptor and glutamate receptors of mollusc and insect, and is characterised by the absence of activity of monocationic drugs and the strong dependence of dicationic once on the internitrogen distance in the drug molecule. The second group includes NMDA receptor and both nicotinic cholinoreceptors. Contrary, here the blocking potency of monocations and dications are practically equal irrespective of molecule length. The data obtained suggest that hydrophobic and nucleophilic components of the binding site are located close to each other in the channels of the NMDA receptor type but are separated by approximately 10 A in the AMPA receptor channel.
Subject(s)
Adamantane/pharmacology , Excitatory Amino Acid Antagonists/pharmacology , Phencyclidine/pharmacology , Receptors, Glutamate/physiology , Adamantane/analogs & derivatives , Animals , Brain/physiology , Cations , Cats , Diptera , Ganglia, Invertebrate/physiology , Ganglia, Sympathetic/physiology , In Vitro Techniques , Mollusca , Neuromuscular Junction/physiology , Rana temporaria , Rats , Rats, Wistar , Receptors, AMPA/antagonists & inhibitors , Receptors, AMPA/physiology , Receptors, Glutamate/drug effects , Receptors, N-Methyl-D-Aspartate/antagonists & inhibitors , Receptors, N-Methyl-D-Aspartate/physiologyABSTRACT
Parenteral administration of des-BOC-Pentagastrin induced the anxiety and fear manifestations, depressing also explorative behaviour in open field experiments in rats. Intranasal administration evoked similar effects, whereas pentagastrin reduced the anxiety level, increasing explorative behaviour. Pentagastrin and des-BOC-Pentagastrin displayed antagonism at the receptor level.
Subject(s)
Anxiety/physiopathology , Oligopeptides/pharmacology , Pentagastrin/analogs & derivatives , Administration, Intranasal , Animals , Avoidance Learning/drug effects , Exploratory Behavior/drug effects , Fear/drug effects , Injections, Intraperitoneal , Male , Motor Activity/drug effects , Oligopeptides/administration & dosage , Pentagastrin/administration & dosage , Pentagastrin/pharmacology , Rats , Rats, Wistar , Receptors, Cholecystokinin/drug effectsABSTRACT
An attempt was made to examine the regulatory effect of bifidumbacterin on the recovery of immunological and hemopoietic homeostasis in mice. Bifidumbacterin feeding to healthy animals had no effect, except for the below-normal values reaching the statistically mean characteristic of mice of this strain. Bifidumbacterin stimulated lymphoiesis in animals immunocompromized by the administration of antilymphocytic antibodies or radiation, but the values being no higher than the normal ones. The same action was seen with erythropoiesis during postradiation loss of red blood cells. The activation or suppression of erythro- or myelopoiesis, which was not caused by direct damage to these cellular populations, but which occurred with the activation of nonspecific T helpers or T suppressors in impairments or recovery of the count of circulating mature lymphocytes under the action of bifidumbacterin, was blocked.
Subject(s)
Anti-Infective Agents/pharmacology , Biological Products/pharmacology , Hematopoiesis/drug effects , Immune Tolerance/drug effects , Animals , Disease Models, Animal , Hematopoiesis/physiology , Immune Tolerance/immunology , Immunity/drug effects , Immunity/radiation effects , Mice , Mice, Inbred C57BL , Mice, Inbred CBA , Remission InductionABSTRACT
Automated analyzer intended for analysis of human blood assesses the main parameters of murine blood with high accuracy and good reproducibility. Differentiation of murine leukocyte by this analyzer is objectively impossible, but it permits the investigation of some characteristics heretofore difficult to study because the routine methods were inaccurate (assessment of the mean size of red cells and platelets or of the mean content of hemoglobin per red cell). Analysis of these values is useful, among other things, in simulation of various anemias in mice.
Subject(s)
Blood Cells/cytology , Hematologic Diseases/diagnosis , Hematology/instrumentation , Animals , Autoanalysis/instrumentation , Blood Platelets/cytology , Erythrocytes/cytology , Hematocrit , Hematologic Diseases/blood , Hemoglobinometry , Leukocytes/cytology , Mice , Mice, Inbred C57BL , Mice, Inbred CBAABSTRACT
The effect of vaccination with diphtheria toxoid (AD-M) on TNF and IL-6 production has been studied in humans. In the present study it was demonstrated that immunization with AD-M resulted in changes of in vitro TNF and IL-6 production by peripheral blood mononuclear cells. TNF release was suppressed but IL-6 production was stimulated. On the other hand, serum levels of TNF were markedly increased over a period of 3 weeks. It was also demonstrated that the postvaccinal cytokine production disturbances may be corrected by pretreatment with a new synthetic hexapeptid (Imunofan((R))). It is possible that the imunofan treatment could prevent some postvaccinal complications.
Subject(s)
Alcohol Dehydrogenase/immunology , Alcoholism/therapy , Behavior, Animal , Immunotherapy, Active , Animals , Male , RatsABSTRACT
The possible biochemical and immunological mechanisms of the previously discovered phenomenon of significant and prolonged decrease of alcohol abuse of albino rats after the intravenous injection of the heterologous alcohol dehydrogenase (ADH) were studied. It was found that immunization of rats against horse liver S-ADH result in the appearance of a high titre of antibodies against rat liver ADH-3 isozyme. This isozyme is responsible for the metabolism of 90% of alcohol administrated in vivo. It is shown that immunization against horse liver S-ADH leads also to a significant (2--3-fold) lowering of the activity level of ADH-3 in rat liver. The activity level of the other rat ADH isozymes, ADH-1 and ADH-2, was not found to be changed. The intravenous injection of the specific anti-(horse liver S-ADH) serum, purified by affinity chromatography on immobilized horse liver S-ADH, resulted in a significant decrease of alcohol abuse in alcohol-dependent animals. These results allow us to assume an important role of rat liver ADH-3 in the mechanism of alcohol addiction.
Subject(s)
Alcohol Dehydrogenase/immunology , Alcohol Dehydrogenase/metabolism , Alcohol Drinking , Alcoholism/immunology , Immunization , Isoenzymes/metabolism , Liver/enzymology , Alcohol Dehydrogenase/isolation & purification , Alcoholism/enzymology , Animals , Antibodies/blood , Antibodies/isolation & purification , Blotting, Western , Electrophoresis, Polyacrylamide Gel , Horses , Isoenzymes/isolation & purification , Male , RatsABSTRACT
The effects of homo- and heterologous alcohol dehydrogenase (ADH) administration into albino rats were investigated. It was found that homologous ADH increases and heterologous ADH decreases the craving for ethanol. The latter effect was accompanied by the appearance of anti-ADH-3 antibodies and by a decrease in ADH-3 activity in the liver. Craving for alcohol decreased after both active and passive immunization against ADH.
Subject(s)
Alcohol Dehydrogenase/pharmacology , Alcohol Drinking , Alcoholism/metabolism , Isoenzymes/metabolism , Liver/enzymology , Alcohol Dehydrogenase/administration & dosage , Alcohol Dehydrogenase/immunology , Alcohol Dehydrogenase/metabolism , Animals , Behavior, Addictive , Enzyme-Linked Immunosorbent Assay , Horses , Immunization, Passive , Rats , VaccinationABSTRACT
A homogenous protein of 120,000 mol. wt isolated from black widow spider (Lactrodectus mactans tredecimguttatus) venom and referred to as alpha-latroinsectotoxin was highly potent (4 nM) in the induction of an increase of the frequency of miniature excitatory postsynaptic potentials in blowfly (Calliphora vicina) larvae neuromuscular preparations. In the frog nerve ending, however, even 50 nM alpha-latroinsectotoxin failed to affect transmitter release. Pretreatment of insect preparations with alpha-latrotoxin or frog preparations with alpha-latroinsectotoxin did not prevent the specific effect of consequent applications of alpha-latroinsectotoxin (insect) and alpha-latrotoxin (frog), respectively. The binding of labelled [125I]alpha-latroinsectotoxin to insect and [125I]alpha-latrotoxin to bovine membrane preparations was saturable and highly specific. The presynaptic effect, but not the binding of alpha-latroinsectotoxin, was dependent on the presence of divalent cations in the external medium. Mg2+ could readily substitute for Ca2+ and increase of transmitter release induced by alpha-latroinsectotoxin also occurred in Ca(2+)-free solutions. Pretreatment of preparations with 300 micrograms/ml concanavalin A completely abolished both the presynaptic effect of alpha-latroinsectotoxin and its binding to insect membrane preparations. Thus, the phenomenology of alpha-latroinsectotoxin action on insects resembles in general that described for the action of alpha-latrotoxin on vertebrates. The selectivity of alpha-latrotoxin and alpha-latroinsectotoxin seems to be due to differences in the structure of neurotoxin receptors in nerve endings of vertebrates and insects, although the mode of presynaptic action has a great deal in common.