Mechanism Of Cell Destruction Research Articles

C-Reactive Protein Enhances IgG-Mediated Cellular Destruction Through IgG-Fc Receptors in vitro.

Antibody-mediated blood disorders ensue after auto- or alloimmunization against blood cell antigens, resulting in cytopenia. Although the mechanisms of cell destruction are the same as in immunotherapies targeting tumor cells, many factors are still unknown. Antibody titers, for example, often do not strictly correlate with clinical outcome. Previously, we found C-reactive protein (CRP) levels to be elevated in thrombocytopenic patients, correlating with thrombocyte counts, and bleeding severity. Functionally, CRP amplified antibody-mediated phagocytosis of thrombocytes by phagocytes. To investigate whether CRP is a general enhancer of IgG-mediated target cell destruction, we extensively studied the effect of CRP on in vitro IgG-Fc receptor (FcγR)-mediated cell destruction: through respiratory burst, phagocytosis, and cellular cytotoxicity by a variety of effector cells. We now demonstrate that CRP also enhances IgG-mediated effector functions toward opsonized erythrocytes, in particular by activated neutrophils. We performed a first-of-a-kind profiling of CRP binding to all human FcγRs and IgA-Fc receptor I (FcαRI) using a surface plasmon resonance array. CRP bound these receptors with relative affinities of FcγRIa = FcγRIIa/b = FcγRIIIa > FcγRIIIb = FcαRI. Furthermore, FcγR blocking (in particular FcγRIa) abrogated CRP's ability to amplify IgG-mediated neutrophil effector functions toward opsonized erythrocytes. Finally, we observed that CRP also amplified killing of breast-cancer tumor cell line SKBR3 by neutrophils through anti-Her2 (trastuzumab). Altogether, we provide for the first time evidence for the involvement of specific CRP-FcγR interactions in the exacerbation of in vitro IgG-mediated cellular destruction; a trait that should be further evaluated as potential therapeutic target e.g., for tumor eradication.

Changes in iron content in brain structures during aging and associated neurodegenerative diseases

The literature data on changes in the content of iron and its metabolites in brain structures during aging and neurodegenerative diseases (Parkinson's disease - PD and Alzheimer's disease - AD) are analyzed. It was revealed that with aging, the iron content in nigrostriatal formations of brain changes: the level of non-heme iron and ferritin increases and neuromelanin also accumulates in neurons of black substance. The accumulation of neuromelanin in combination with increase in ferritin content can be considered as a morphochemical sign of neuroprotective effect of nervous tissue during aging. The iron level in PD and AD compared with that during physiological aging continues to increase, and the ability of chelating agents to bind iron decreases (ferritin in neuroglia cells and neuromelanin in neurons), which activates the mechanisms of cell destruction. As a result, in PD, the aggregation of α-synuclein is disrupted, which leads to the formation of Levi bodies, and in AD, the amyloid beta precursor protein (APP) undergoes proteolysis and this leads to the formation of amyloid plaques, which triggers subsequent neurodegenerative changes, including the death of neurons.

Non-Temperature Induced Effects of Magnetized Iron Oxide Nanoparticles in Alternating Magnetic Field in Cancer Cells.

This paper reports the damaging effects of magnetic iron-oxide nanoparticles (MNP) on magnetically labeled cancer cells when subjected to oscillating gradients in a strong external magnetic field. Human breast cancer MDA-MB-231 cells were labeled with MNP, placed in the high magnetic field, and subjected to oscillating gradients generated by an imaging gradient system of a 9.4T preclinical MRI system. Changes in cell morphology and a decrease in cell viability were detected in cells treated with oscillating gradients. The cytotoxicity was determined qualitatively and quantitatively by microscopic imaging and cell viability assays. An approximately 26.6% reduction in cell viability was detected in magnetically labeled cells subjected to the combined effect of a static magnetic field and oscillating gradients. No reduction in cell viability was observed in unlabeled cells subjected to gradients, or in MNP-labeled cells in the static magnetic field. As no increase in local temperature was observed, the cell damage was not a result of hyperthermia. Currently, we consider the coherent motion of internalized and aggregated nanoparticles that produce mechanical moments as a potential mechanism of cell destruction. The formation and dynamics of the intracellular aggregates of nanoparticles were visualized by optical and transmission electron microscopy (TEM). The images revealed a rapid formation of elongated MNP aggregates in the cells, which were aligned with the external magnetic field. This strategy provides a new way to eradicate a specific population of MNP-labeled cells, potentially with magnetic resonance imaging guidance using standard MRI equipment, with minimal side effects for the host.

Acetyl-L-Carnitine and Nicotinamide for Prevention of Type 1 Diabetes. I-Literature Review which Gave Support to the Treatment. II-Case Report, Evaluation of Five Years Treatment

In the first part, this article review the accepted knowledge of type 1 diabetes, its physiopathology, the importance of cytokines and the induction of apoptosis and necrosis during its evolution. Throughout this work we describe in more detail the inhibition of this mechanism of cell destruction by acetyl-L-carnitine and nicotinamide. We also explain the complementary action of their association which gave support to the treatment. In the second part, we present the complete evolution of 8 children treated with the oral medication of 50 mg/Kg of acetyl-L-carnitine plus 25 mg/Kg of nicotinamide during 5 years. We published the first 2 years of evolution under treatment in these children (JPEM 26: 347, 2013). The children had positive auto-antibodies and were consanguineous of type 1 diabetic patients. The intravenous glucose tolerance test (IVGTT) showed a first phase of insulin release minor of 48 μU to enter in the protocol, and the same test was used for children evolution. Seven out eight children stopped the treatment because they normalized the metabolic parameters and no one became diabetic. All children increased the insulin response to IVGTT (between 1.44 to 5.69 times). Along the treatment, seven of these eight children turned their positive auto-antibodies into negatives.

Editorial (Thematic Issue: Regulating the CNS Grand Regulator; N-methyl-D-aspartate Receptor-Mediated Neurotransmission)

Editorial (Thematic Issue: Regulating the CNS Grand Regulator; N-methyl-D-aspartate Receptor-Mediated Neurotransmission)

Role of nonsynaptic GluN2B-containing NMDA receptors in excitotoxicity: Evidence that fluoxetine selectively inhibits these receptors and may have neuroprotective effects

In acute ischaemic brain injury and chronic neurodegeneration, the primary step leading to excitotoxicity and cell death is the excessive and/or prolonged activation of glutamate (Glu) receptors, followed by intracellular calcium (Ca(2+)) overload. These steps lead to several effects: a persistent depolarisation of neurons, mitochondrial dysfunction resulting in energy failure, an increased production of reactive oxygen species (ROS), an increase in the concentration of cytosolic Ca(2+) [Ca(2+)]i, increased mitochondrial Ca(2+) uptake, and the activation of self-destructing enzymatic mechanisms. Antagonists for NMDA receptors (NMDARs) are expected to display neuroprotective effects, but no evidence to support this hypothesis has yet been reported. A number of clinical trials using NMDAR antagonists have failed to demonstrate neuroprotective effects, either by reducing brain injury or by preventing neurodegeneration. Recent advances in NMDAR research have provided an explanation for this phenomenon. Synaptic and extrasynaptic NMDARs are composed of different subunits (GluN2A and GluN2B) that demonstrate opposing effects. Synaptic GluN2A-containing and extrasynaptic GluN2B-containing NMDARs have different co-agonists: d-serine for synaptic NMDARs and glycine for extrasynaptic NMDARs. Both co-agonists are of glial origin. The mechanisms of cell destruction or cell survival in response to the activation of NMDAR receptors depend in part on [Ca(2+)]i and the route of entry of this ion and more significantly on the subunit composition and localisation of the NMDARs. While synaptic NMDAR activation is involved in neuroprotection, the stimulation of extrasynaptic NMDARs, which are composed of GluN2B subunits, triggers cell destruction pathways and may play a key role in the neurodegeneration associated with Glu-induced excitotoxicity. In addition, it has been found that synaptic and extrasynaptic NMDA receptors have opposing effects in determining the fate of neurons. This result has led to the targeting of nonsynaptic GluN2B-containing NMDARs as promising candidates for drug research. Under hypoxic conditions, it is likely that the failure of synaptic glutamatergic transmission, the impairment of the GluN2A-activated neuroprotective cascade, and the persistent over-activation of extrasynaptic GluN2B-containing NMDARs lead to excitotoxicity. Fluoxetine, a drug widely used in clinical practice as an antidepressant, has been found to selectively block GluNR2B-containing NMDARs. Therefore, it seems to be a potential candidate for neuroprotection.

Elevated Complement (C) and IgG Bound Microparticles (MP) in Immune Thrombocytopenic Purpura (ITP) and Hemolytic Anemia (HA).

Abstract 1313Poster Board I-337 BackgroundCell derived microparticles (MP) are shed during cell activation and apotosis and MP profiles reflect the status of cell disturbances in various forms of pancytopenias. It was demonstrated that when antibodies fix complement (C) on the membrane, red cells evade C mediated lysis by shedding MP with bound C. We analyzed C and IgG bound to MP to gain insight on the underlying mechanisms of cell destruction. We measured C1q fragment and IgG on cell-derived (MP) in plasmas of patients with ITP, hemolytic anemias (HA) and thrombosis (TBS). Methods(1) Patient population. Consenting patients consisted of 18 TBS, 14 ITP and 6 HA (5 AIHA and 1 TTP), as well as 20 normal controls (NC). (2) Flow cytometry. MP were centrifuged from 1 mL fresh (not frozen) platelet-poor plasma (PPP), washed twice with saline, resuspended in 100 μL, then incubated with fluorescent mAb to C1q and IgG, then analyzed by flow cytometry. In addition, MP in the PPP were analyzed for MP from RBC (RMP) using marker glycophorin A, and MP from platelets (PMP) by CD42b. Values were considered elevated if >2SD above the mean of NC. Control values were (mean ±SD per μL): C1q+ MP = 536 ±151; IgG+ MP = 5,542 ±2,081; RMP = 823 ±246; PMP = 7,520 ±2,084. ResultsWe observed significant elevation of C1q+ and IgG+ MP in patients with ITP (2-3 fold) and hemolytic anemias (6-10 fold) but not in those with thrombosis. These findings indicate that complement mediated cell destruction or disturbance in these disorders is frequent. (1). The ITP group consisted of 2 subgroups, one of which had elevated C1q+ and IgG+ MP, the other not, and these subgroups also differed in RMP. Specifically, six ITP with high C1q+ MP also had high RMP (1,899 ±682 /μL) and PMP (16,602 ±4,216 /μL) while those with normal C1q+ MP had normal RMP (504 ±186 /μL) and PMP (3,472 ±1196 /μL). This suggests that platelet destruction in ITP can proceed via C in some but not all cases, probably depending on the autoantibodies. We have previously reported high RMP in ITP. These findings suggest subclinical C mediated hemolysis in a subset of ITP. (2) In HA patients, all 6 had elevated C1q+ MP (3,934 ±1,419 /μL, p<0.001) as compared to normal controls (536 ±151 /μL). The mean in HA was nearly 6-fold greater than NC. The HA group also had higher IgG+ MP, with mean counts about 10-fold higher than NC (61,531 ±20,733 vs. 5,542 ±2,081 /μL, p<0.001). Furthermore, the HA patients also had elevated RMP (2,191 ±635 /μL, p<0.01). This suggests that C-mediated destruction of RBC is a major mechanism in HA. (3) Linear regression analysis showed that C1q+ MP is well correlated with IgG+ MP (R = 0.84, p<0.0001) and RMP (R = 0.79, p<0.001). (4) The TBS group did not show higher levels of any of the measures assayed.It is widely believed that phagocytosis is the mechanism of cell destruction in ITP and AIHA. Our findings support the concept that complement (C) -mediated platelet or red cell destruction play an important role and is common in these disorders. Assay of C and IgG on MP can provide new insight to underlying mechanisms of immune mediated platelet and red cell destruction. DisclosuresNo relevant conflicts of interest to declare.

Involvement of both caspase-dependent and -independent pathways in apoptotic induction by hexaminolevulinate-mediated photodynamic therapy in human lymphoma cells

Photodynamic therapy (PDT) is a cancer treatment based on the interaction of a photosensitizer, light and oxygen. PDT with the endogenous photosensitizer, protoporphyrin IX (PpIX) induced by 5-aminolevulinic acid (ALA) or its derivatives is a modification of this treatment modality with successful application in dermatology. However, the mechanism of cell destruction by ALA-PDT has not been elucidated. In this study a human T-cell lymphoma Jurkat cell line was treated with PDT using hexaminolevulinate (HAL, hexylester of ALA). Four hours following treatment nearly 80% of the cells exhibited typical apoptotic features. Mitochondrial pro-apoptotic proteins were evaluated by Western blots in subcellular fractionated samples. PDT caused cytosolic translocation of cytochrome c and nuclear redistribution of apoptosis-inducing factor (AIF), but the release of mitochondrial Smac/DIABLO, Omi/HtrA2 and EndoG was not observed. The release of cytochrome c was followed by the cleavage of caspase-9 and caspase-3 as well as its downstream substrates, together with oligonucleosomal DNA fragmentation. The pan-caspases inhibitor, z-VAD.fmk, prevented oligonucleosomal DNA fragmentation, but failed to inhibit PDT-mediated apoptosis. The apoptotic induction by AIF-mediated caspase-independent pathway was also found after HAL-PDT with large-scale DNA fragmentation in the presence of z-VAD.fmk. These results demonstrate that cytochrome c-mediated caspase-dependent pathway and AIF-induced caspase-independent pathway are simultaneously involved in the apoptotic induction by PDT. When the cytochrome c-induced caspase-dependent pathway is blocked, the cells go into apoptosis via AIF-mediated pathway, clearly demonstrating that the cytochrome c-mediated caspase-dependent pathway is not required for such apoptotic induction. This finding may have an impact on improved PDT effectiveness.

Role of peroxidases in Parkinson disease: a hypothesis

Extensive research has been done to elucidate the underlying molecular events causing neurodegenerative diseases such as Parkinson disease, yet the cause and the individual steps in the progression of such diseases are still unknown. Here we advance the hypothesis that, rather than or in addition to inorganic radical molecules, heme-containing peroxidase enzymes may play a major role in the etiology of Parkinson disease. This hypothesis is based on the following considerations: (1) several heme-containing enzymes with peroxidase activity are present in the substantia nigra pars compacta; (2) these peroxidases have the ability to catalyze the oxidation of proteins and lipids; (3) certain heme peroxidases are known to destroy cells in vivo; (4) heme peroxidases have the stability and specificity that could account for the fact that specific molecules and cells are subject to damage in Parkinson disease, rather than a random destruction; (5) heme peroxidase activity could account for certain reactions in connection with parkinsonism that thus far have not been adequately explained; and (6) the participation of a heme peroxidase could explain some recent observations that are inconsistent with the oxyradical theory. The peroxidase-catalyzed oxidative pathway proposed here does not preclude the participation of apoptosis as an additional mechanism for cell destruction.

Rituximab (monoclonal anti-CD20 antibody): mechanisms of action and resistance.

Rituximab, a chimeric monoclonal antibody targeted against the pan-B-cell marker CD20, was the first monoclonal antibody to be approved for therapeutic use. Treatment with rituximab at standard weekly dosing is effective in more than 50% of patients with relapsed or refractory CD20-positive follicular non-Hodgkin's lymphoma, but is not curative. It is less effective in other subtypes of CD20-positive lymphoma and for retreatment, even with CD20 still expressed. Thus, binding of rituximab to CD20 is not sufficient to kill many lymphoma cells, indicating that there are mechanisms of resistance. Mechanisms of cell destruction that have been demonstrated to be activated by rituximab binding to CD20 include direct signaling of apoptosis, complement activation and cell-mediated cytotoxicity. The relative importance of each of these mechanisms in determining clinical response to rituximab treatment remains a matter of conjecture. Thus, the role of various resistance pathways, some documented in experimental systems and others still hypothetical, remains uncertain. Resistance could potentially be mediated by alterations in CD20 expression or signaling, elevated apoptotic threshold, modulation of complement activity or diminished cellular cytotoxicity. As the first of an expanding class of anticancer agents, lessons learned regarding the mechanism of rituximab action and resistance will be of increasing importance.

Cytopénies immunologiques

Anaemias, thrombocytopenias and neutropenias can result from aggressions by auto, allo or drug dependant antibodies. Clinical features are often suggestive of the immune mechanism of cell destruction. According to the mechanism and the lineage involved. biological methods are more or less helpful for positive diagnosis. Added to classical direct and indirect antiglobulin tests the gel test offers a new practical approach to the immunological diagnosis of immune anaemia. This recent technology is currently under study in order to evaluate its actual relevance in diagnosis and characterisation of these pathologies. Due to its lack of specificity, the evaluation of platelet associated IgG has not proven helpful in diagnosis of autoimmune thrombocytopenias. The MAIPA test is more promising and seems to be more efficient in the study of different kind of immune thromnbocytopenias, but its complexity leads to restrict it to clinical cases in which a biological proof is essential. The very short survival of granulocytes in-vitro adds to the complexity of granulocyte immunology which is still reserved to highly specialised laboratories. However in cautiously selected cases immunological studies can be conclusive in the diagnosis of auto or alloimmune neutropenias. To day the study of drug dependant antibody remains still limited to clinical research.

Recombinant human IgG molecules lacking Fcgamma receptor I binding and monocyte triggering activities.

Subclasses of human IgG have a range of activity levels with different effector systems but each triggers at least one mechanism of cell destruction. We are aiming to engineer non-destructive human IgG constant regions for therapeutic applications where depletion of cells bearing the target antigen is undesirable. The attributes required are a lack of killing via Fcgamma receptors (R) and complement but retention of neonatal FcR binding to maintain placental transport and the prolonged half-life of IgG. Eight variants of human IgG constant regions were made with anti-RhD and CD52 specificities. The mutations, in one or two key regions of the CH2 domain, were restricted to incorporation of motifs from other subclasses to minimize potential immunogenicity. IgG2 residues at positions 233 - 236, substituted into IgG1 and IgG4, reduced binding to FcgammaRI by 10(4)-fold and eliminated the human monocyte response to antibody-sensitized red blood cells, resulting in antibodies which blocked the functions of active antibodies. If glycine 236, which is deleted in IgG2, was restored to the IgG1 and IgG4 mutants, low levels of activity were observed. Introduction of the IgG4 residues at positions 327, 330 and 331 of IgG1 and IgG2 had no effect on FcgammaRI binding but caused a small decrease in monocyte triggering.

Hematology: Neutrophils Fight Infectious Disease but May Promote Other Human Pathologies

Continued human survival through numerous bouts of infectious disease depends on the nonspecific defense response mediated by neutrophils. Their microbiocidal response consists of both oxidative and nonoxidative mechanisms of cell destruction that are activated as they migrate from the vasculature to sites of infection in the tissues. Reactive oxidants produced during this response are implicated as causative factors underlying a number of inflammatory disorders and carcinogenic events. This article reviews and updates current understanding of neutrophil function in both fighting infectious disease and promoting inflammatory-induced disease.

Flecanide-induced immune neutropenia. Documentation of a hapten-mediated mechanism of cell destruction

Immune-mediated granulocytopenia due to cardiac antiarrhythmic medications is a rare, but potentially dangerous, event. This article characterizes the first case, to our knowledge, of severe granulocytopenia associated with the administration of flecanide acetate, a new class I antiarrhythmic drug. Immunologic studies determined that flecanide was capable of binding to the surface of normal neutrophils. The patient's serum contained an IgG antibody that could specifically bind to the haptenized neutrophils, presumably mediating enhanced destruction of mature granulocytes both in the serum and within the bone marrow. Cessation of flecanide therapy resulted in resolution of the granulocytopenia. The titer of antineutrophil antibody in the patient's serum decreased to background levels within the next five months. Similar antibodies were not found in serum from nonsensitized individuals. The capacity of flecanide to bind to normal neutrophils may prove to be a significant risk factor for the subsequent development of antineutrophil antibodies and agranulocytosis in patients receiving this drug. Careful hematologic monitoring of all patients who are receiving this medication is, therefore, strongly urged.

On the mechanism of microbial cell destruction during ballistic disintegration processes

Schizosaccharomyces pombe cells were used to determine the mechanism of cell destruction. The values of breaking point of the cell wall substance at the varied temperatures of destruction had been determined to obtain the necessary results. It was established that the cells are destroyed because of forces resulting from the gradient movement of the medium near the surface of the milling bodies. The destructible part of the cell wall is preliminarily weakened by the influence of high temperature.

Lymphocyte in vitro cytotoxicity: specific release of lymphotoxin-like materials from tuberculin-sensitive lymphoid cells.

ALLOGRAFT immunity and delayed hypersensitivity reactions are caused chiefly by the action of host immune lymphoid cells1. Although these reactions have been much studied in vivo and in vitro, the mechanism of cell destruction is essentially unknown. There have been reports from this laboratory that a cell-free toxic factor released by immune and phytohaemagglutinin (PHA)-stimulated non-immune mouse lymphocytes is essential in the in vitro destruction of target L cells2. This factor, termed lymphotoxin (LT), caused in vitro cytolysis of both continuous and primary cells obtained from many animal species3. Later work showed that lymphocytes from various animal species, including man, could be stimulated in vitro to release LT, in the absence of target cells, by treatments which induce lymphocyte transformation, that is the mixed lymphocyte reaction, PHA and xenogeneic antibody4. It was therefore of interest to investigate whether lymphoid cells obtained from animals with delayed hypersensitivity to soluble antigens could be induced in vitro to release LT-like materials. We wish to report here that in the case of tuberculin hypersensitivity in mice, guinea-pigs and man, non-specific toxic materials are released when the cells are cultured in the presence of specific antigen.

A MECHANISM OF CELL DESTRUCTION IN INDIVIDUALS SENSITIZED TO FOREIGN ANTIGENS AND ITS IMPLICATIONS IN AUTO-IMMUNITY. COMBINED CLINICAL STAFF CONFERENCE AT THE NATIONAL INSTITUTES OF HEALTH.

Excerpt Drug purpura (1-6), drug hemolytic anemia (7-9), and drug leukopenia (10-12) are now classic examples of diseases in which sensitization to a foreign antigen causes destruction of the sensi...

Action of antibodies and plasmin on Ehrlich ascites tumour cells.

THE mechanism of cell destruction in allergic inflammation is not well understood. Two explanations for production of cell damage have, however, been proposed: (a) that the antigen-antibody reaction causes, in some non-specific manner, permeability changes in cells which result in the release of active mediators of inflammation (histamine, etc.) and that the latter are directly involved in the allergic process1; (b) that the antigen-antibody reaction activates proteolytic enzymes (plasmin, proteases) that injure the cells2–4.

Comparative biochemical studies on normal and on poliomyelitis virus-infected tissue cultures. V. Profund alteration of acid and alkaline phosphatase activity in infected rhesus kidney cells.

Experimental evidence is presented for drastic changes in phosphomonoesterase activities of tissue cultures, brought about by infection with poliomyelitis viruses. Acid phosphatase activity went through a maximum before decreasing almost to zero level. Alkaline phosphatase activity diminished progressively to zero, then with disruption of the cells attamed normal levels. Various aspects of the kinetics were investigated and illustrated. The initial increase of acid phosphatase, in contrast with the alkaline, may mean that the reactions catalyzed by this enzyme continue during the early phase. This period is the time of intense virus production and therefore it was supposed that this enzyme may play some role in virus synthesis. It was assumed that the virus acts as a particle of molecular size and becomes associated with the enzyme complex physicochemically or chemically. This association ends with the disintegration of the host cells. During the cell-virus interaction a toxin may develop which is a strong and general enzyme inhibitor. Various enzyme systems differ in sensitivity toward these virus effects; for instance, acid phosphatase is irreversibly inhibited or may be destroyed. The visible CPE of virus is preceded by a drastic reduction of enzyme activities in whole TC and in its various fractions, which may suggest causal relationship in the mechanism of cell destruction. In arrested or latent infection these processes are operative, but on a smaller scale. The drop in activities cannot be explained by the reduction of tissue mass, which is the consequence, rather than the cause, of enzyme changes. Besides the theoretical significance of these observations the following practical points can be summarized: 1. Changes in phosphatase activities are most strikingly demonstrated in whole tissue cultures inoculated with poliomyelitis virus. 2. There is causal relationship among infection, enzyme changes, and transformation of cell physiology. 3. The biochemical approach provides a quantitative measure of the extent of cell damage, before visible CPE is detectible. 4. Unapparent and active infections with poliomyelitis virus could be differentiated from normal controls by this method. 5. By various manipulations (freezing, long incubation) the difference between normal and infected TC can be enhanced. Suitable technical methods were proposed for various types of investigations.

Production of Lesions in the Central Nervous System with Focused Ultrasound: A Study of Dosage Factors

Applications of ultrasonics in neurosurgery involve the production of lesions of a specified size at a specified location, and in a reproducible fashion. Control of the dosage required for a given lesion depends on the geometry of the focal region, the exact determination of focal intensity and the relation between irradiation parameters and biological effect. From an analysis of these factors an optimum frequency for each focal depth is determined and an empirical dosage relationship based on ultrasonically produced paralysis in mice is stated. The mechanism of cell destruction by ultrasound is shown to be a temperature-dependent mechanical effect originating at weak points in the tissue. The difficulties in extrapolating results obtained with experimental animals to applications in human neurosurgery are pointed out.