Co-expression of truncated and full-length tau induces severe neurotoxicity.

Abundant tau inclusions are a defining hallmark of several human neurodegenerative diseases, including Alzheimer's disease. Protein fragmentation is a widely observed event in neurodegenerative proteinopathies. The relevance of tau fragmentation for the neurodegenerative process in tauopathies has yet remained unclear. Here we found that co-expression of truncated and full-length human tau in mice provoked the formation of soluble high-molecular-weight tau, the failure of axonal transport, clumping of mitochondria, disruption of the Golgi apparatus and missorting of synaptic proteins. This was associated with extensive nerve cell dysfunction and severe paralysis by the age of 3 weeks. When the expression of truncated tau was halted, most mice recovered behaviorally and functionally. In contrast, co-expression of full-length tau isoforms did not result in paralysis. Truncated tau thus induces extensive but reversible neurotoxicity in the presence of full-length tau through the formation of nonfilamentous high-molecular-weight tau aggregates, in the absence of tau filaments. Targeting tau fragmentation may provide a novel approach for the treatment of human tauopathies.

Invited review: Prion-like transmission and spreading of tau pathology.

Filaments made of hyperphosphorylated tau protein are encountered in a number of neurodegenerative diseases referred to as 'tauopathies'. In the most prevalent tauopathy, Alzheimer's disease, tau pathology progresses in a stereotypical manner with the first lesions appearing in the locus coeruleus and the entorhinal cortex from where they appear to spread to the hippocampus and neocortex. Propagation of tau pathology is also characteristic of argyrophilic grain disease, where the tau lesions appear to spread throughout distinct regions of the limbic system. These findings strongly implicate neurone-to-neurone propagation of tau aggregates. Isoform composition and morphology of tau filaments can differ between tauopathies suggesting the existence of conformationally diverse tau strains. Altogether, this points to prion-like mechanisms in the pathogenesis of tauopathies.

Tauopathies with parkinsonism: clinical spectrum, neuropathologic basis, biological markers, and treatment options.

Tauopathies with parkinsonism represent a spectrum of disease entities unified by the pathologic accumulation of hyperphosphorylated tau protein fragments within the central nervous system. These pathologic characteristics suggest shared pathogenetic pathways and possible molecular targets for disease-modifying therapeutic interventions. Natural history studies, for instance, in progressive supranuclear palsy, frontotemporal dementia with parkinsonism linked to chromosome 17, corticobasal degeneration, and Niemann-Pick disease type C as well as in amyotrophic lateral sclerosis/Parkinson-dementia complex permit clinical characterization of the disease phenotypes and are crucial to the development and validation of biological markers for differential diagnostics and disease monitoring, for example, by use of neuroimaging or proteomic approaches. The wide pathologic and clinical spectrum of the tauopathies with parkinsonism is reviewed in this article, and perspectives on future advances in the understanding of the pathogenesis are given, together with potential therapeutic strategies.

Lentivirus Tau (P301S) expression in adult amyloid precursor protein (APP)-transgenic mice leads to tangle formation.

AIMS: In this study, we aimed to investigate the interaction between amyloid- and Tau-associated pathologies to gain further insights into the development of Alzheimer's disease. We examined the formation of neurofibrillary tangles (NFT) in adult mouse brain without the prior overexpression of Tau at embryonic or early post-natal stages to dissociate any developmental mechanisms. METHODS: Lentivirus technology was used to examine the effects of overexpressing mutant Tau-P301S in the adult mouse brains of both wild-type and amyloid precursor protein (APP)-transgenic mice. RESULTS: We find that injection of lentivirus Tau-P301S into the hippocampus of adult wild-type mice increases levels of hyperphosphorylated Tau, as early as 3 months post injection. However, no NFT are found even after 13 months of Tau expression. In contrast, the overexpression of Tau-P301S in adult APP-transgenic animals results in the formation of Gallyas-stained NFT. CONCLUSIONS: Our current findings are the first to show that overexpression of Tau-P301S in adult mice overexpressing APP, but not wild-type mice, leads to enhanced Tau-related pathology.

Hereditary systemic angiopathy (HSA) with cerebral calcifications, retinopathy, progressive nephropathy, and hepatopathy.

Several hereditary conditions affecting cerebral, retinal and systemic microvessels have recently been described. They include CADASIL, CRV, and HERNS. We here report on a variant form of a hereditary systemic angiopathy (HSA) affecting two generations of a Caucasian family. Clinical symptoms of HSA appear in the mid-forties and are characterized by visual impairment, migraine-like headache, skin rash, epileptic seizures, progressive motor paresis and cognitive decline. Late symptoms include hepatic and renal failure. Retinal capillary microaneurysms and arteriolar tortuosity are associated with marked optic disc atrophy. Radiological hallmarks consist of multiple cerebral calcifications and tumor-like subcortical white matter lesions. Brain, peripheral nerve, muscle, kidney and colon biopsies have revealed a multi organ small vessel involvement with partly altered endothelium, perivascular inflammation and thrombotic microangiopathy. No curative therapeutic options are known for hereditary cerebral vasculopathies. The use of cyclophosphamide, azathioprine and methotrexate was of no benefit in our cases of HSA. Early diagnosis of hereditary systemic angiopathies is important in order to prevent patients from repetitive invasive diagnostic measures and to avoid the use of inappropriate and potentially harmful drugs.

New insights into the pathology of Parkinson's disease: does the peripheral autonomic system become central?

Recent studies in aged, neurologically unimpaired subjects have pointed to a specific induction site of the pathological process of Parkinson's disease (PD) in the region of the dorsal glossopharyngeus-vagus complex as well as in the anterior olfactory nucleus. From the lower brainstem, the disease process would then pursue an ascending course and involve more rostral brainstem areas, limbic structures, and eventually the cerebral cortex. One barrier to the acceptance of the caudal medullary structures as the induction site of PD pathology is that not all parts of the nervous system have been investigated for the presence of PD-associated lesions in cases of early asymptomatic PD. Using alpha-synuclein immunostaining, we investigated the brain, the sacral, and thoracic autonomic nuclei of the spinal cord as well as several components of the peripheral autonomic nervous system in a autopsy cohort of 98 neurologically unimpaired subjects aged 64 or more. Our data indicate that the autonomic nuclei of the spinal cord and the peripheral autonomic nervous system belong to the most constantly and earliest affected regions next to medullary structures and the olfactory nerves in neurologically unimpaired older individuals, thus providing a pathological basis for early premotor autonomic dysfunctions at a prodromal stage of PD.

The validity of clinical diagnoses of dementia in a group of consecutively autopsied memory clinic patients.

BACKGROUND: Epidemiological studies show that up to 10% of individuals aged 65 years and older suffer from dementia, most commonly from dementia of the Alzheimer Type (DAT) (1). Clinicopathological studies are critical to our understanding of this disease and improving the accuracy of clinical diagnoses. OBJECTIVES: Our objectives were to examine the validity of clinical diagnoses of DAT, to determine the prevalence of different forms of dementia in this sample, and to investigate the relationship between age at death and polymorbidity. SUBJECTS AND METHOD: Clinical data were available from 221 patients who had been examined at the Basel Memory Clinic between 1986 and 1996. From this population, 34% (75 patients) were autopsied in the Department of Pathology, University Hospital Basel, and neuropathological examinations were additionally performed on 62 (83%) of these patients. Clinical and neuropathological data were retrospectively compared. RESULTS: 67.8% of the neuropathologically examined patients received a definitive diagnosis of AD (Alzheimer's disease), vascular dementia (VaD) or mixed dementia (AD and VaD). AD alone or with other histopathological hallmarks of dementia was the most prevalent neuropathological diagnosis (63%). VaD was deemed the only cause of dementia in only 4.8% of patients. The sensitivity for DAT was 75.9%, the specificity 60.6%. Increasing age was associated with an increasing number of clinical and neuropathological diagnoses. CONCLUSION: The sensitivity and specificity of the clinical diagnoses of DAT found in our study are similar to previous reports (2-5). Older patients had more etiologies of their dementia than younger patients. This study reaffirms the need for internationally accepted criteria for clinical and neuropathological diagnoses, as well as further clinical-neuropathological investigations to further refine the clinical diagnostic process.

[Primary cerebellar T-cell lymphoma]. / Primäres zerebelläres T-Zell-Lymphom.

Primary central nervous system T-cell lymphomas are rare and have to be differentiated from reactive lesions. It is therefore essential to use all possible tools to establish the diagnosis, including immunohistochemistry, molecular genetic analysis, and/or cytogenetic methods. In this paper we present the case of a primary cerebellar T-cell lymphoma in a 50-year-old man; a clonal T-cell receptor gene rearrangement was documented. After two cycles of methotrexate therapy the patient developed Pneumocystis carinii-induced pneumonia, dying 10 weeks after his diagnosis. The autopsy did not reveal any residual tumour.

Determinants of diagnostic investigation sensitivities across the clinical spectrum of sporadic Creutzfeldt-Jakob disease.

To validate the provisional findings of a number of smaller studies and explore additional determinants of characteristic diagnostic investigation results across the entire clinical spectrum of sporadic Creutzfeldt-Jakob disease (CJD), an international collaborative study was undertaken comprising 2451 pathologically confirmed (definite) patients. We assessed the influence of age at disease onset, illness duration, prion protein gene (PRNP) codon 129 polymorphism (either methionine or valine) and molecular sub-type on the diagnostic sensitivity of EEG, cerebral MRI and the CSF 14-3-3 immunoassay. For EEG and CSF 14-3-3 protein detection, we also assessed the influence of the time point in a patient's illness at which the investigation was performed on the likelihood of a typical or positive result. Analysis included a large subset of patients (n = 743) in whom molecular sub-typing had been performed using a combination of the PRNP codon 129 polymorphism and the form of protease resistant prion protein [type 1 or 2 according to Parchi et al. (Parchi P, Giese A, Capellari S, Brown P, Schulz-Schaeffer W, Windl O, Zerr I, Budka H, Kopp N, Piccardo P, Poser S, Rojiani A, Streichemberger N, Julien J, Vital C, Ghetti B, Gambetti P, Kretzschmar H. Classification of sporadic Creutzfeldt-Jakob disease based on molecular and phenotypic analysis of 300 subjects. Ann Neurol 1999; 46: 224-233.)] present in the brain. Findings for the whole group paralleled the subset with molecular sub-typing data available, showing that age at disease onset and disease duration were independent determinants of typical changes on EEG, while illness duration significantly influenced positive CSF 14-3-3 protein detection; changes on brain MRI were not influenced by either of these clinical parameters, but overall, imaging data were less complete and consequently conclusions are more tentative. In addition to age at disease onset and illness duration, molecular sub-type was re-affirmed as an important independent determinant of investigation results. In multivariate analyses that included molecular sub-type, time point of the investigation during a patient's illness was found not to influence the occurrence of a typical or positive EEG or CSF 14-3-3 protein result. A typical EEG was most often seen in MM1 patients and was significantly less likely in the MV1, MV2 and VV2 sub-types, whereas VV2 patients had an increased likelihood of a typical brain MRI. Overall, the CSF 14-3-3 immunoassay was the most frequently positive investigation (88.1%) but performed significantly less well in the very uncommon MV2 and MM2 sub-types. Our findings confirm a number of determinants of principal investigation results in sporadic CJD and underscore the importance of recognizing these pre-test limitations before accepting the diagnosis excluded or confirmed. Combinations of investigations offer the best chance of detection, especially for the less common molecular sub-types such as MV2 and MM2.

Pathology and genetics of frontotemporal lobar degeneration: an update.

Frontotemporal lobar degeneration (FTLD) is a common form of dementia that usually afflicts patients in their mid-life. Clinically, patients with FTLD present with changes in behavior and/or language dysfunction. According to their underlying neuropathological substrate, these neurodegenerative conditions can now be classified into two main groups: those with tau pathology (tauopathies), and those without tau pathology. In the majority of nontauopathy disorders the recently identified TAR DNA-binding protein-43 (TDP-43) is found as the major inclusion protein (TDP-43 proteinopathies), and TDP-43 is also present in motor neuron inclusions of amyotrophic lateral sclerosis. Presently, mutations in 4 genes (MAPT, PGRN, VCP, CHMP2B) are known to cause diverse types of FTLD pathology. Here, we summarize the recent neuropathological and genetic advances in FTLD research.

Becker muscular dystrophy with marked divergence between clinical and molecular genetic findings: case series.

Both Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are caused by mutations of the X-linked dystrophin gene. BMD patients are less affected clinically than DMD patients. We present five patients with a diagnosis of BMD. First, two identical twins, with a deletion of exon 48 of the dystrophin gene, who experienced prominent muscle cramps from the age of three. The histopathological examination of muscle biopsies of these two twins revealed only very slight muscle fiber alterations. Second, two brothers who displayed marked, unusual intrafamilial variability of the clinical picture as well as showing a new point mutation in the dystrophin gene. And finally, a fifth boy who displayed a new point mutation in the dystrophin gene. Although he was clinically asymptomatic at the age of 15 and muscle biopsy only showed very minor myopathic signs, serum Creatine Kinase (CK) levels had been considerably elevated for years. Taken together, these cases add to the spectrum of marked discrepancies in clinical, histopathological and molecular genetic findings in BMD.

PTEN-independent induction of caspase-mediated cell death and reduced invasion by the focal adhesion targeting domain (FAT) in human astrocytic brain tumors which highly express focal adhesion kinase (FAK).

Increased expression of focal adhesion kinase (FAK) was consistently observed in low- and high-grade astrocytomas and during glioblastoma progression after radiotherapy, but not in the more benign oligodendroglioma. In glioblastoma cell lines deficient for p53, p16(INK4A), and p14(ARF), FAK was inhibited in a dominant-negative manner by the focal adhesion targeting (FAT) domain, reducing invasion. In addition, caspase-3 activity was increased after serum withdrawal, or by cisplatin in the presence of serum, or upon loss of substrate attachment, and was in each case independent of PTEN status. Our results identify FAK as a potential target for anti-invasive strategies against infiltrating glioma cells.

DMBT1 encodes a protein involved in the immune defense and in epithelial differentiation and is highly unstable in cancer.

The gene deleted in malignant brain tumors 1 (DMBT1) has been proposed as a candidate tumor suppressor for brain, gastrointestinal, and lung cancer. It codes for a protein of unknown function belonging to the superfamily of scavenger receptor cysteine-rich proteins. We aimed at getting insights into the functions of DMBT1 by expression analyses and studies with a monoclonal antibody against the protein. The DMBT1 mRNA is expressed throughout the immune system, and Western blot studies demonstrated that isoforms of DMBT1 are identical to the collectin-binding protein gp-340, a glycoprotein that is involved in the respiratory immune defense. Immunohistochemical analyses revealed that DMBT1 is produced by both tumor-associated macrophages and tumor cells and that it is deregulated in glioblastoma multiforme in comparison to normal brain tissue. Our data further suggest that the proteins CRP-ductin and hensin, both of which have been implicated in epithelial differentiation, are the DMBT1 orthologs in mice and rabbits, respectively. These findings and the spatial and temporal distribution of DMBT1 in fetal and adult epithelia suggest that DMBT1 further plays a role in epithelial development. Rearrangements of DMBT1 were found in 16 of 18 tumor cell lines, and hemizygous deletions were observed in a subset of normal individuals, indicating that the alterations in tumors may be a result of both pre-existing deletions uncovered by a loss of heterozygosity and secondary changes acquired during tumorigenesis. Thus, DMBT1 is a gene that is highly unstable in cancer and encodes for a protein with at least two different functions, one in the immune defense and a second one in epithelial differentiation.

Synaptic dysfunction, memory deficits and hippocampal atrophy due to ablation of mitochondrial fission in adult forebrain neurons.

Well-balanced mitochondrial fission and fusion processes are essential for nervous system development. Loss of function of the main mitochondrial fission mediator, dynamin-related protein 1 (Drp1), is lethal early during embryonic development or around birth, but the role of mitochondrial fission in adult neurons remains unclear. Here we show that inducible Drp1 ablation in neurons of the adult mouse forebrain results in progressive, neuronal subtype-specific alterations of mitochondrial morphology in the hippocampus that are marginally responsive to antioxidant treatment. Furthermore, DRP1 loss affects synaptic transmission and memory function. Although these changes culminate in hippocampal atrophy, they are not sufficient to cause neuronal cell death within 10 weeks of genetic Drp1 ablation. Collectively, our in vivo observations clarify the role of mitochondrial fission in neurons, demonstrating that Drp1 ablation in adult forebrain neurons compromises critical neuronal functions without causing overt neurodegeneration.

Spontaneous hemorrhagic stroke in a mouse model of cerebral amyloid angiopathy.

A high risk factor for spontaneous and often fatal lobar hemorrhage is cerebral amyloid angiopathy (CAA). We now report that CAA in an amyloid precursor protein transgenic mouse model (APP23 mice) leads to a loss of vascular smooth muscle cells, aneurysmal vasodilatation, and in rare cases, vessel obliteration and severe vasculitis. This weakening of the vessel wall is followed by rupture and bleedings that range from multiple, recurrent microhemorrhages to large hematomas. Our results demonstrate that, in APP transgenic mice, the extracellular deposition of neuron-derived beta-amyloid in the vessel wall is the cause of vessel wall disruption, which eventually leads to parenchymal hemorrhage. This first mouse model of CAA-associated hemorrhagic stroke will now allow development of diagnostic and therapeutic strategies.

Antibody mediated lysis of hapten-conjugated target cells by macrophages and by complement: the influence of IgG subclass, antibody and hapten density.

Lysis of 51Cr-labeled TNP-SRBC sensitised by rat IgG1 or IgG2a type antibodies by homologous, paraffin oil-elicited peritoneal macrophages (ADCC) or by homologous complement was studied. IgG2a was found to be markedly more efficient in mediating both ADCC and complement dependent lysis compared to IgG1. Inhibition of the ADCC pointed to the involvement of separate but partially overlapping interaction sites for the two isotypes. We suggest that FcRII type receptors play a favoured role in both IgG2a and IgG1 mediated ADCC. The threshold amount of bound antibody required for ADCC was lower than that sufficient for complement dependent lysis regardless on the subclass or on hapten density. The extent of lysis (both ways) was found to depend on hapten density using equal amounts of antibody. The results are interpreted as terms of the possible requirements for association of IgG molecules on the target cell surface.

Interaction between rat peritoneal macrophages and sensitised erythrocytes: dependence on IgG subclass, antibody density and the degree of hapten conjugation.

The interaction between macrophages (M phi) and antibody sensitised target cells was studied by the use of rat peritoneal macrophages, TNP hapten conjugated sheep red blood cells (SRBC) and homologous antibodies of subclasses IgG1 and IgG2a. Under optimal conditions, the great majority of the M phi formed rosettes with IgG1-sensitised antibodies while a maximum of 50% was achieved when target cells were sensitised by IgG2a. Using a double rosette technique, the major part of rosette-forming cells was found to bind both of the isotypes. IgG1-mediated rosette formation was observed at very low degrees of sensitisation as opposed to IgG2a-mediated target cell binding. Not only the amount of bound antibody but also the degree of hapten conjugation (epitope density) appear to influence the ratio of rosette-forming cells. IgG1-mediated rosette formation was partially inhibited by monomeric IgG1 and more efficiently by soluble ovalbumin (OVA)-anti-OVA complexes involving IgG1-type antibodies, while IgG2a mediated rosette formation was inhibited by OVA-anti-OVA complexes containing IgG2a type antibodies, and less efficiently by complexes involving IgG1. No inhibition was found by monomeric IgG2a. Based on the present data, we propose that two types of receptors are involved in the interaction of M phi and target cells coated by IgG1 and/or IgG2a type antibodies. One requires a multiple antibody-receptor interaction, binding both subclasses at overlapping binding sites; the other is able to interact with IgG1 and does not depend on the multiplicity of interactions.

Rat IgG subclasses mediating binding and phagocytosis of target cells by homologous macrophages.

Attachment and ingestion of 51Cr-labelled TNP-SRBC sensitized by rat IgG1, IgG2a or IgG2b-type antibodies by homologous, elicited peritoneal macrophages were studied. IgG1 was found to be the most efficient isotype in mediating these functions. The antibody doses required for a significant attachment were found to differ with the isotype of Ab, while doses needed for a significant phagocytosis and antibody-dependent cellular cytotoxicity (ADCC) varied between 400-700 Ab/SRBC with all the isotypes studied. Both binding and phagocytosis were also influenced by the degree of hapten conjugation when target cells were sensitized by IgG1. Inhibition of these functions by soluble immune complexes and monomeric immunoglobulins suggests the involvement of two Fc gamma R in binding of the three isotypes. Based on the present work and on previous results we conclude that IgG2a interacts with a receptor binding complexed IgG only (Fc gamma RII), IgG2b binds to a different receptor which appears to bind monomeric ligand as well (Fc gamma RI), while IgG1 seems to interact with both types of receptor. We propose that phagocytosis can be mediated by both Fc gamma RI and Fc gamma RII.

Phosphorylated protein kinases associated with neuronal and glial tau deposits in argyrophilic grain disease.

Tau phosphorylation was examined in argyrophilic grain disease (AGD) by using the phosphospecific tau antibodies Thr181, Ser202, Ser214, Ser 396 and Ser422, and antibodies to non-phosphorylated and phosphorylated mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinases (ERK), stress-activated kinase (SAPK), c-Jun N-terminal kinase (JNK), p38 kinase (p-38), alpha-calcium/calmodulin-dependent kinase II (alphaCaM kinase II), and glycogen synthase kinase-3 (GSK-3), all of which regulate phosphorylation at specific sites of tau. This is the first study in which the role of protein kinases in tau phosphorylation has been examined in AGD. Hyperphosphorylated tau accumulated in grains and pre-tangles in the hippocampus, dentate gyrus, entorhinal and trans-entorhinal cortices, and amygdala in all cases. Ballooned neurons in the amygdala, entorhinal, insular and cingulate cortex, and claustrum contained alphaB-crystallyn and phosphorylated neurofilament epitopes. Some astrocytes and scattered oligodendrocytes containing coiled bodies were recognized with anti-tau antibodies. A few tangles were observed in the entorhinal cortex and hippocampus corresponding to Alzheimer's disease (AD) stages I-III of Braak and Braak. None of the present cases was associated with progressive supranuclear palsy or with alpha-synuclein pathology. Two bands of phospho-tau of 64 and 68 kDa were observed in Western blots of sarkosyl-insoluble fractions enriched with abnormal filaments in AGD, a pattern that contrasts with the 4-band pattern obtained in AD. No modifications in the expression of non-phosphorylated MEK-1, ERK2 and GSK-3alpha/beta, as revealed by immunohistochemistry, were seen in AGD, but sarkosyl-insoluble fractions were particularly enriched in JNK-1 and alphaCaM kinase II. Increased expression of the phosphorylated (P) forms of MAPK/ERK, SAPK/JNK, p38 and GSK-3beta was found in grains and tau-containing cells in AGD. MAPK/ERK-P immunoreactivity was observed in pre-tangles and, diffusely, in the cytoplasm of ballooned neurons, but not in grains. Strong SAPK/JNK-P and P38-P, and moderate GSK-3b-P immunoreactivities selectively occured in grains, in neurons with pre-tangles and in the peripheral region of the cytoplasm of ballooned neurons. MAPK/ERK-P, SAPK/JNK-P, p38-P and GSK-3beta-P were expressed in tau-containing astrocytes and in oligodendrocytes with coiled bodies. Western blots revealed kinase expression in sarkosyl-insoluble fractions but none of the phospho-kinase antibodies recognized hyper-phosphorylated tau protein. These findings indicate complex, specific profiles of tau phosphorylation and concomitant activation of precise kinases that have the capacity to phosphorylate tau at specific sites in AGD. These kinases co-localize abnormal tau in selected structures and cells, including neurons with pre-tangles, ballooned neurons, astrocytes and oligodendrocytes. Most of these kinases are involved in cell death and cell survival in certain experimental paradigms. However, double-labeling studies with the method of in situ end-labeling of nuclear DNA fragmentation and cleaved (active) caspase-3 immunohistochemistry show no expression of apoptosis and death markers in cells bearing phosphorylated kinases.

Sodium-cromoglycate (Cromolyn) selectively increases the binding and phagocytosis of unsensitized target cells by rat peritoneal macrophages.

The influence of sodium-cromoglycate (cromolyn) on the binding and ingestion of sheep erythrocytes (SRBC) by elicited rat peritoneal macrophages (M phi) was studied using unsensitized SRBC. SRBC sensitized by homologous IgG or by IgM and complement as target cells. Preincubation of M phi with the drug (1 nM/1-2 mM/1) markedly enhanced both binding and ingestion of uncoated SRBC. The IgG-related increment in binding and phagocytosis was not significantly influenced by the drug. When target cells were coated by IgM and complement cromolyn pretreatment was ineffective. Preincubation of M phi by bovine brain gangliosides (BBG) diminished the cromolyn-induced enhancement of target cell binding and phagocytosis. When SRBC were pretreated by BBG, an increase of binding and phagocytosis was observed. These data suggest that cromoglycate may enhance the capacity of M phi to bind erythrocytes via ganglioside structures. Coating SRBC by complement components appears to interfere with binding of erythrocytes to M phi ganglioside receptors.