Quantitative microglia morphological features correlate with diffusion MRI in 2-month-old 3xTg-AD mice

Microglia (MØ) morphologies are closely related to their functional state and have a central role in the maintenance of brain homeostasis. It is well known that inflammation contributes to neurodegeneration at later stages of Alzheimer's Disease, but it is not clear which role MØ-mediated inflammation may play earlier in the disease pathogenesis. We have previously reported that diffusion MRI (dMRI) is able to detect early myelin abnormalities present in 2-month-old 3xTg-AD (TG) mice; since MØ actively participate in regulating myelination, the goal of this study was to assess quantitatively MØ morphological characteristics and its association with dMRI metrics patterns in 2-month-old 3xTg-AD mice. Our results show that, even at this young age (2-month-old), TG mice have statistically significantly more MØ cells, which are overall smaller and more complex, compared with age-matched normal control mice (NC). Our results also confirm that myelin basic protein is reduced in TG mice, particularly in fimbria (Fi) and cortex. Additionally, MØ morphological characteristics, in both groups, correlate with several dMRI metrics, depending on the brain region examined. For example, the increase in MØ number correlated with higher radial diffusivity (r = 0.59, p = 0.008), lower fractional anisotropy (FA) (r = -0.47, p = 0.03), and lower kurtosis fractional anisotropy (KFA) (r = -0.55, p = 0.01) in the CC. Furthermore, smaller MØ cells correlate with higher axial diffusivity) in the HV (r = 0.49, p = 0.03) and Sub (r = 0.57, p = 0.01). Our findings demonstrate, for the first time, that MØ proliferation/activation are a common and widespread feature in 2-month-old 3xTg-AD mice and suggest that dMRI measures are sensitive to these MØ alterations, which are associated in this model with myelin dysfunction and microstructural integrity abnormalities.

Brain microstructure abnormalities in the 3xTg-AD mouse - A diffusion MRI and morphology correlation study

The widely studied triple transgenic (3xTg-AD) mouse provides a robust model of Alzheimer's disease (AD) with region dependent patterns of progressive amyloid-β (Aß) and tau pathology. Using diffusion MRI (dMRI), we investigated the sensitivity of dMRI measures in capturing AD pathology associated microstructure alterations in older 3xTg-AD mice, and the degree to which dMRI changes correlate with measurements of Aβ and tau pathology. 3xTg-AD and normal control (NC) mice, 15 to 21 months of age, were used in this study. In vivo dMRI data were acquired for the generation of diffusion tensor (DT) and diffusional kurtosis (DK) measures within the hippocampus and fimbria (Fi). For these same brain regions, Aβ and tau pathology were quantified by morphological analysis of Aß1-42 and AT8 immunoreactivity. Two-tailed, two-sample t-tests were performed to assess group differences in each brain region of interest (ROI), with the Benjamini-Hochberg false discovery rate (FDR) method being applied to adjust for multiple comparisons. Spearman correlation coefficients were calculated to investigate associations between diffusion and morphological measures. Our results revealed, depending on the brain region, DT and DK measures were able to detect group differences. In the dorsal hippocampus (HD), fractional anisotropy (FA) was significantly higher in the 3xTg-AD mice compared with NC mice. In the subiculum (SUB), FA, axial diffusivity (D||) and radial kurtosis (K┴) were significantly higher in 3xTg-AD mice compared with NC mice. Morphological quantification of Aß1-42 and AT8 immunoreactivity showed elevated Aß and tau in the Fi, ventral hippocampus (HV) and SUB of 3xTg-AD mice. The presence of Aβ and tau was significantly correlated with several DT and DK measures, particularly in the SUB, where an increase in tau correlated with an increase in mean kurtosis (MK) and K┴. This work demonstrates significant dMRI differences between older 3xTg-AD and NC mice in the hippocampus and Fi. Significant correlations were found between dMRI and morphological measures of Aβ and tau pathology. These results support the potential of dMRI-derived parameters as biomarkers of AD pathology. Since the imaging methods employed here are easily translatable to clinical MRI, our results are also relevant for human AD patients.

Magnetic resonance imaging reveals microemboli-mediated pathological changes in brain microstructure in diabetic rats: relevance to vascular cognitive impairment/dementia

Diabetes doubles the risk of vascular cognitive impairment, but the underlying reasons remain unclear. In the present study, we determined the temporal and spatial changes in the brain structure after microemboli (ME) injection using diffusion MRI (dMRI). Control and diabetic rats received cholesterol crystal ME (40-70 µm) injections. Cognitive tests were followed up to 16 weeks, while dMRI scans were performed at baseline and 12 weeks post-ME. The novel object recognition test had a lower d2 recognition index along with a decrease in spontaneous alternations in the Y maze test in diabetic rats with ME. dMRI showed that ME injection caused infarction in two diabetic animals (n=5) but none in controls (n=6). In diabetes, radial diffusivity (DR) was increased while fractional anisotropy (FA) was decreased in the cortex, indicating loss of tissue integrity and edema. In the dorsal hippocampus, mean diffusivity (MD), axial diffusivity (DA), and DR were significantly increased, indicating loss of axons and myelin damage. Histological analyses confirmed more tissue damage and microglial activation in diabetic rats with ME. These results suggest that ME injury and associated cerebrovascular dysfunction are greater in diabetes, which may cause cognitive deficits. Strategies to improve vascular function can be a preventive and therapeutic approach for vascular cognitive impairment.

Abstract TMP109: Isosorbide Mononitrate And Cilostazol Treatment Prevents Temporal Changes In The Brain Microstructure Of Diabetic Rats Following Microemboli Injection: Relevance To Vascular Cognitive Impairment And Dementia (VCID)

Diabetes doubles the risk of VCID, but underlying reasons for this are not understood and preventive therapeutic strategies are lacking. We showed that diabetic but not control rats develop progressive cognitive decline in a microemboli (ME) model of VCID. Given that cerebrovascular dysfunction is a common pathology between diabetes and VCID, we hypothesized that improvement of endothelial function in diabetes prevents ME-mediated white matter injury. Our treatment paradigm was based on the ongoing LACI-2 trial which assesses the efficacy of isosorbide mononitrate (ISMN) and cilostazol (CZL) in the prevention of small vessel disease (SVD) progression. Seven-eight weeks after diabetes onset, control and diabetic rats were treated with ISMN/CZL for 4 weeks, then injected with cholesterol ME and monitored longitudinally using three different MRI parameters - diffusion tensor imaging (DTI), diffusional kurtosis imaging (DKI) and cerebral blood flow (CBF). We previously reported decreased fractional anisotropy and increased diffusivity at 12 weeks after ME injection in diabetic rats, indicating possible loss of tissue integrity in the cortex and hippocampus. In the current study, we detected a time effect in both groups for DTI and DKI metrics (measured in cortex and corpus callosum as shown in the table as well as in hippocampus, internal and external capsule) but in most of them there was no disease/group-effect. Also, CBF was higher in diabetic rats at all time points. This suggests that drug treatment with ISMN/CZL before ME injection prevented the possible deleterious effects of the latter in the diabetic rats by improving the endothelial integrity and it is a viable preventive and possibly therapeutic strategy for VCID.

Fiber Ball White Matter Modeling Reveals Microstructural Alterations in Healthy Brain Aging

Age-related white matter degeneration is characterized by myelin breakdown and neuronal fiber loss that preferentially occur in regions that myelinate later in development. Conventional diffusion MRI (dMRI) has demonstrated age-related increases in diffusivity but provide limited information regarding the tissue-specific changes driving these effects. A recently developed dMRI biophysical modeling technique, Fiber Ball White Matter (FBWM) modeling, offers enhanced biological interpretability by estimating microstructural properties specific to the intra-axonal and extra-axonal spaces. We used FBWM to illustrate the biological mechanisms underlying changes throughout white matter in healthy aging using data from 63 cognitively unimpaired adults ages 45-85 with no radiological evidence of neurodegeneration or incipient Alzheimer's disease. Conventional dMRI and FBWM metrics were computed for two late-myelinating (genu of the corpus callosum and association tracts) and two early-myelinating regions (splenium of the corpus callosum and projection tracts). We examined the associations between age and these metrics in each region and tested whether age was differentially associated with these metrics in late- vs. early-myelinating regions. We found that conventional metrics replicated patterns of age-related increases in diffusivity in late-myelinating regions. FBWM additionally revealed specific intra- and extra-axonal changes suggestive of myelin breakdown and preferential loss of smaller-diameter axons, yielding in vivo corroboration of findings from histopathological studies of aged brains. These results demonstrate that advanced biophysical modeling approaches, such as FBWM, offer novel information about the microstructure-specific alterations contributing to white matter changes in healthy aging. These tools hold promise as sensitive indicators of early pathological changes related to neurodegenerative disease.

Diffusion MRI detects basal forebrain cholinergic abnormalities in the 3xTg-AD mouse model of Alzheimer's disease

Degeneration of the basal forebrain (BF) is detected early in the course of Alzheimer's disease (AD). Reduction in the number of BF cholinergic (ChAT) neurons associated with age-related hippocampal cholinergic neuritic dystrophy is described in the 3xTg-AD mouse model; however, no prior diffusion MRI (dMRI) study has explored the presence of BF alterations in this model. Here we investigated the ability of diffusion MRI (dMRI) to detect abnormalities in BF microstructure for the 3xTg-AD mouse model, along with related pathology in the hippocampus (HP) and white matter (WM) tracks comprising the septo-hippocampal pathway. 3xTg-AD and normal control (NC) mice were imaged in vivo using the specific dMRI technique known as diffusional kurtosis imaging (DKI) at 2, 8, and 15 months of age, and 8 dMRI parameters were measured at each time point. Our results revealed significant lower dMRI values in the BF of 2 months-old 3xTg-AD mice compared with NC mice, most likely related to the increased number of ChAT neurons seen in this AD mouse model at this age. They also showed significant age-related dMRI changes in the BF of both groups between 2 and 8 months of age, mainly a decrease in fractional anisotropy and axial diffusivity, and an increase in radial kurtosis. These dMRI changes in the BF may be reflecting the complex aging and pathological microstructural changes described in this region. Group differences and age-related changes were also observed in the HP, fimbria (Fi) and fornix (Fx). In the HP, diffusivity values were significantly higher in the 2 months-old 3xTg-AD mice, and the HP of NC mice showed a significant increase in axial kurtosis after 8 months, reflecting a normal pattern of increased fiber density complexity, which was not seen in the 3xTg-AD mice. In the Fi, mean and radial diffusivity values were significantly higher, and fractional anisotropy, radial kurtosis and kurtosis fractional anisotropy were significantly lower in the 2 months-old 3xTg-AD mice. The age trajectories for both NC and TG mice in the Fi and Fx were similar between 2 and 8 months, but after 8 months there was a significant decrease in diffusivity metrics associated with an increase in kurtosis metrics in the 3xTg-AD mice. These later HP, Fi and Fx dMRI changes probably reflect the growing number of dystrophic neurites and AD pathology progression in the HP, accompanied by WM disruption in the septo-hippocampal pathway. Our results demonstrate that dMRI can detect early cytoarchitectural abnormalities in the BF, as well as related aging and neurodegenerative changes in the HP, Fi and Fx of the 3xTg-AD mice. Since DKI is widely available on clinical scanners, these results also support the potential of the considered dMRI parameters as in vivo biomarkers for AD disease progression.

Abstract P739: Magnetic Resonance Imaging-Based Comparison of Temporal Changes in Brain Microstructure After Microemboli Injection in Control and Diabetic Rats: Relevance to Vascular Cognitive Impairment/Dementia

Diabetes doubles the risk of VCID but underlying reasons remain unclear. We reported that diabetic animals are more prone to microemboli (ME)-mediated tissue damage/demyelination and progressive cognitive decline. The goal of the current study was to determine the temporal and spatial changes in cerebral blood flow (CBF) and brain structure after ME injection using MRI. At 10 weeks after onset of diabetes, control and diabetic rats received cholesterol crystal ME (40-70 μm) injection. MRI scans were performed at baseline, weeks 8 and 12 post-ME. Behavioral tests including novel object recognition (NOR) and Y-maze for cognitive function and gait analysis with CatWalk were conducted at same time points as well as week 16. Diabetic animals had baseline deficits in certain cognitive domains and progressively worsened. ME injection caused infarction in two of the diabetic animals (n=6) but were not detected in controls (n=8). Diffusion Tensor Imaging (DTI) metrics showed lower axial diffusivity (DA) in the cortex of diabetic animals, indicating a degree of axonal damage. Post ME, radial diffusivity (DR) was increased while fractional anisotropy (FA) was decreased in the cortex at week 12. At the dorsal hippocampus, mean (MD), DA and DR were all significantly increased by week 12. These changes may reflect loss of tissue integrity and edema in the cortex and loss of axons and myelin damage in the hippocampus of diabetic animals after ME injection. Diabetic animals also showed a significant increase of CBF at week 8 particularly at the dorsal hippocampus and thalamus, which returned to normal by week 12. These results suggest that ME injury and associated cognitive deficits are greater in diabetes, which also causes cerebrovascular dysfunction, and strategies to improve vascular function can be a preventive and therapeutic strategy for VCID.

Diffusion MRI detects early brain microstructure abnormalities in 2-month-old 3×Tg-AD mice

The 3×Tg-AD mouse is one of the most studied animal models of Alzheimer's disease (AD), and develops both amyloid beta deposits and neurofibrillary tangles in a temporal and spatial pattern that is similar to human AD pathology. Additionally, abnormal myelination patterns with changes in oligodendrocyte and myelin marker expression are reported to be an early pathological feature in this model. Only few diffusion MRI (dMRI) studies have investigated white matter abnormalities in 3×Tg-AD mice, with inconsistent results. Thus, the goal of this study was to investigate the sensitivity of dMRI to capture brain microstructural alterations in 2-month-old 3×Tg-AD mice. In the fimbria, the fractional anisotropy (FA), kurtosis fractional anisotropy (KFA), and radial kurtosis (K┴ ) were found to be significantly lower in 3×Tg-AD mice than in controls, while the mean diffusivity (MD) and radial diffusivity (D┴ ) were found to be elevated. In the fornix, K┴ was lower for 3×Tg-AD mice; in the dorsal hippocampus MD and D┴ were elevated, as were FA, MD, and D┴ in the ventral hippocampus. These results indicate, for the first time, dMRI changes associated with myelin abnormalities in young 3×Tg-AD mice, before they develop AD pathology. Morphological quantification of myelin basic protein immunoreactivity in the fimbria was significantly lower in the 3×Tg-AD mice compared with the age-matched controls. Our results demonstrate that dMRI is able to detect widespread, significant early brain morphological abnormalities in 2-month-old 3×Tg-AD mice.

Abstract WP473: Diabetic Male and Female Rats Are More Susceptible to Infarction and Cognitive Decline in a Microemboli Based Model of Vascular Cognitive Impairment

Diabetes increases the risk of VCID but underlying reasons remain unclear. We reported that diabetes-mediated early cerebrovascular dysfunction facilitates the entrapment of microemboli (ME) and results in demyelination/neurodegeneration 6 weeks after ME injection in male diabetic but not control rats. Cognitive decline became apparent by week 8 and further amplified by week 12 in diabetes. The goals of the current study were to determine whether ME injection 1) mediates demyelination and cognitive decline in females, 2) activates microglia and promotes inflammation, 3) causes gait abnormalities and 4) mediates changes in cerebral blood flow (CBF) and brain structure as determined by diffusion MRI. Diabetes was induced by a high fat diet and low dose streptozotocin (35 mg/kg) injection in male and female Wistar rats. After 8 weeks onset of diabetes, control and diabetic rats received cholesterol crystal ME (40-70 μm) injection. In study 1, histology was done at week 6 after injection (3000 crystals) to determine early structural changes and cognition was assessed by novel object recognition (NOR) test. In Study 2, MRI, gait (stand on catwalk) and NOR tests were done at baseline and week 8 after injection (6000 crystals) in male rats and will be further monitored at weeks 12 and 16. Diabetic animals developed inflammation, demyelination, and neurodegeneration associated with cognitive decline that was greater than that observed in males (TABLE). In Study 2, initial analyses show higher infarct score and lower CBF after ME injection with no gait pattern change in diabetic male rats. Longitudinal measurements at weeks 12 & 16 will demonstrate the disease progression. These data suggest that 1) endothelial dysfunction renders diabetic animals more susceptible to infarction and subsequent cognitive decline caused by ME, and 2) intervention strategies can be tried in this clinically relevant model of VCID.

Diffusion MRI detects longitudinal white matter changes in the 3xTg-AD mouse model of Alzheimer's disease

The sensitivity of multiple diffusion MRI (dMRI) parameters to longitudinal changes in white matter microstructure was investigated for the 3xTg-AD transgenic mouse model of Alzheimer's disease, which manifests both amyloid beta plaques and neurofibrillary tangles. By employing a specific dMRI method known as diffusional kurtosis imaging, eight different diffusion parameters were quantified to characterize distinct aspects of water diffusion. Four female 3xTg-AD mice were imaged at five time points, ranging from 4.5 to 18 months of age, and the diffusion parameters were investigated in four white matter regions (fimbria, external capsule, internal capsule and corpus callosum). Significant changes were observed in several diffusion parameters, particularly in the fimbria and in the external capsule, with a statistically significant decrease in diffusivity and a statistically significant increase in kurtosis. Our preliminary results demonstrate that dMRI can detect microstructural changes in white matter for the 3xTg-AD mouse model due to aging and/or progression of pathology, depending strongly on the diffusion parameter and anatomical region.

Modeling white matter tract integrity in aging with diffusional kurtosis imaging

Myelin breakdown and neural fiber loss occur in aging. This study used white matter tract integrity metrics derived from biophysical modeling using Diffusional Kurtosis Imaging to assess loss of myelin (i.e., extraaxonal diffusivity, radial direction, De,⊥) and axonal density (i.e., axonal water fraction) in cognitively unimpaired older adults. Tract-based spatial statistics and region of interest analyses sought to identify ontogenic differences and age-related changes in white matter tracts using cross-sectional and longitudinal data analyzed with general linear and mixed-effects models. In addition to pure diffusion parameters (i.e., fractional anisotropy, mean diffusivity, mean kurtosis), we found that white matter tract integrity metrics significantly differentiated early- from late-myelinating tracts, correlated with age in spatially distinct regions, and identified primarily extraaxonal changes over time. Percent metric changes were |0.3-0.9|% and |0.0-1.9|% per year using cross-sectional data and longitudinal data, respectively. There was accelerated decline in some late- versus early-myelinating tracts in older age. These results demonstrate that these metrics may inform further study of the transition from age-related changes to neurodegenerative decline.

Novel white matter tract integrity metrics sensitive to Alzheimer disease progression

BACKGROUND AND PURPOSE

Along with cortical abnormalities, white matter microstructural changes such as axonal loss and myelin breakdown are implicated in the pathogenesis of Alzheimer disease. Recently, a white matter model was introduced that relates non-Gaussian diffusional kurtosis imaging metrics to characteristics of white matter tract integrity, including the axonal water fraction, the intra-axonal diffusivity, and the extra-axonal axial and radial diffusivities.

MATERIALS AND METHODS

This study reports these white matter tract integrity metrics in subjects with amnestic mild cognitive impairment (n = 12), Alzheimer disease (n = 14), and age-matched healthy controls (n = 15) in an effort to investigate their sensitivity, diagnostic accuracy, and associations with white matter changes through the course of Alzheimer disease.

RESULTS

With tract-based spatial statistics and region-of-interest analyses, increased diffusivity in the extra-axonal space (extra-axonal axial and radial diffusivities) in several white matter tracts sensitively and accurately discriminated healthy controls from those with amnestic mild cognitive impairment (area under the receiver operating characteristic curve = 0.82-0.95), while widespread decreased axonal water fraction discriminated amnestic mild cognitive impairment from Alzheimer disease (area under the receiver operating characteristic curve = 0.84). Additionally, these white matter tract integrity metrics in the body of the corpus callosum were strongly correlated with processing speed in amnestic mild cognitive impairment (r = |0.80-0.82|, P < .001).

CONCLUSIONS

These findings have implications for the course and spatial progression of white matter degeneration in Alzheimer disease, suggest the mechanisms by which these changes occur, and demonstrate the viability of these white matter tract integrity metrics as potential neuroimaging biomarkers of the earliest stages of Alzheimer disease and disease progression.

Quantitative MRI reveals aging-associated T2 changes in mouse models of Alzheimer's disease

In this study, we used MRI to analyze quantitative parametric maps of transverse (T(2)) relaxation times in a longitudinal study of transgenic mice expressing mutant forms of amyloid precursor protein (APP), presenilin (PS1), or both (PS/APP), modeling aspects of Alzheimer's disease (AD). The main goal was to characterize the effects of progressive beta-amyloid accumulation and deposition on the biophysical environment of water and to investigate if these measurements would provide early indirect evidence of AD pathological changes in the brains of these mice. Our results demonstrate that at an early age before beta-amyloid deposition, only PS/APP mice show a reduced T(2) in the hippocampus and cortex compared with wild-type non-transgenic (NTg) controls, whereas a statistically significant within-group aging-associated decrease in T(2) values is seen in the cortex and hippocampus of all three transgenic genotypes (APP, PS/APP, and PS) but not in the NTg controls. In addition, for animals older than 12 months, we confirmed our previous report that only the two genotypes that form amyloid plaques (APP and PS/APP) have significantly reduced T(2) values compared with NTg controls. Thus, T(2) changes in these AD models can precede amyloid deposition or even occur in AD models that do not deposit beta-amyloid (PS mice), but are intensified in the presence of amyloid deposition.

Application of a non-linear image registration algorithm to quantitative analysis of T2 relaxation time in transgenic mouse models of AD pathology

Transgenic mouse models have been essential for understanding the pathogenesis of Alzheimer's disease (AD) including those that model the deposition process of beta-amyloid (Abeta). Several laboratories have focused on research related to the non-invasive detection of early changes in brains of transgenic mouse models of Alzheimer's pathology. Most of this work has been performed using regional image analysis of individual mouse brains and pooling the results for statistical assessment. Here we report the implementation of a non-linear image registration algorithm to register anatomical and transverse relaxation time (T2) maps estimated from MR images of transgenic mice. The algorithm successfully registered mouse brain magnetic resonance imaging (MRI) volumes and T2 maps, allowing reliable estimates of T2 values for different regions of interest from the resultant combined images. This approach significantly reduced the data processing and analysis time, and improved the ability to statistically discriminate between groups. Additionally, 3D visualization of intra-regional distributions of T2 of the resultant registered images provided the ability to detect small changes between groups that otherwise would not be possible to detect.

HIV infection of human choroid plexus: a possible mechanism of viral entry into the CNS

The present study examines the hypothesis that HIV infection of the choroid plexus (CPx) may be an important site of viral entry into the brain. Formalin-fixed, paraffin-embedded CPx was obtained from 25 patients with AIDS and 13 nonAIDS patients and was processed for light microscopy and for immunohistochemical detection of HIV gp41, T and B lymphocytes, monocytes/macrophages and endothelial cells. Eleven of the 13 nonAIDS CPx were normal and 2 contained inflammatory foci of undetermined etiology. The stroma contained T lymphocytes in all and monocytes in 22%; B lymphocytes and HIV antigen were absent. Choroid plexus of the AIDS cases contained opportunistic infections or lymphoma in 12 and inflammatory foci alone in 6; 7 were normal. T lymphocytes were present in 70% and monocytes in 50%. In addition to the stromal localization, monocytes also were present in supra-epithelial regions and within or adjacent to the capillary endothelium. HIV-positive cells in the CPx were found in 11 cases (44%) and in the supra-epithelial area in another 2. Their presence correlated with neither infection nor lymphoma of the CPx or brain. They were situated in the stroma, supra-epithelial region and (rarely) capillary endothelium. Immunohistochemistry on serial sections identified the HIV-infected cells as monocytes, including those by capillary endothelium and in supra-epithelial areas. The study demonstrates that the CPx contains HIV-infected monocytes in almost half of the cases. Their apposition to endothelium suggests hematogenous origin. These results support the hypothesis that HIV encephalitis may develop from CPx infection.

Histopathology of cerebral toxoplasmosis in human immunodeficiency virus infection: a comparison between patients with early-onset and late-onset acquired immunodeficiency syndrome

We reviewed the histological features of untreated toxoplasmosis in 18 cases with the acquired immunodeficiency syndrome (AIDS), eight of which were surgical biopsies and 10 of which were autopsy specimens. The results were compared according to the clinical status of the patient at the time the diagnosis of toxoplasmosis was made (early-onset v late-onset AIDS) and according to the source of the specimen (surgical biopsy specimen v autopsy specimen). Cerebral toxoplasmosis was the AIDS-defining illness in half of the cases (six surgical biopsy specimens and three autopsy specimens). Inflammation in these cases was moderate in 44% and severe in 56%. Fibrous capsules were found in five cases. Lymphocytes and plasma cells were more prominent than neutrophils. Cerebral toxoplasmosis developed in or was part of the terminal AIDS illness in the remaining nine cases (two surgical biopsy specimens and seven autopsy specimens). In this group inflammation was sparse in 44%, moderate in 55%, and severe in only 11%. Fibrous capsules were usually absent and neutrophils were the predominant cell type. Comparisons between surgical biopsy specimens and autopsy specimens showed moderate to severe inflammation and frequent fibrous encapsulation in all of the former specimens but only in those autopsy specimens in which toxoplasmosis was the initial manifestation of AIDS. Thus, this study demonstrates varied neuropathological patterns of untreated cerebral toxoplasmosis in patients with AIDS and correlates the inflammatory response in the brain with the clinical stage of the patient's human immunodeficiency syndrome (HIV) infection. Inflammation and fibrous encapsulation were common only in patients with early-onset AIDS in whom cerebral toxoplasmosis was the first manifestation of the illness. This study highlights important differences between the histology of this infection at surgical biopsy and at autopsy, and stresses the need to consider toxoplasma as a potential cause of encapsulated brain abscesses.

Immune complex deposition in the choroid plexus of patients with acquired immunodeficiency syndrome

We identified immune complex deposits in the choroid plexus of approximately 75% of patients with acquired immunodeficiency syndrome (AIDS) who had either normal brains or human immunodeficiency virus encephalitis. Since circulating immune complexes are common in AIDS patients, and since local choroid plexus pathology usually was absent, their likely origin is from the bloodstream. Choroid plexus deposits of immune complexes have been implicated in altering the function of this structure or in enhancing its vulnerability to infection. Therefore, immune complex deposition in the choroid plexus of AIDS patients may be responsible for some of the common alterations in the cerebrospinal fluid and for the frequency of opportunistic infections in this region.

Choroid plexus infection in cerebral toxoplasmosis in AIDS patients

We evaluated the postmortem incidence of choroid plexus infection in cerebral toxoplasmosis in 17 patients with acquired immune deficiency syndrome (AIDS) and cerebral toxoplasmosis and, by immunohistochemistry, identified Toxoplasma gondii tachyzoites in this structure in 53% of all cases. They were present in 78% of the nine cases with the acute necrotizing stages of CNS toxoplasmosis but were less frequent (20%) in patients with only the healed cystic lesions of toxoplasmosis. Large necrotizing abscesses of the choroid plexus were found in three of the patients. In one of these, the choroid plexus was the sole site of CNS infection, which presented as radiographically documented masses in the third and fourth ventricles associated with obstructive hydrocephalus. These results demonstrate that infection of the choroid plexus is common with cerebral toxoplasmosis and suggest that this infection should be included in the differential diagnosis of intra- or periventricular lesions in patients with AIDS. In addition, the high frequency of choroid plexus infection with acute cerebral toxoplasmosis suggests that cerebral toxoplasmosis in the immunosuppressed patient may be due to hematogenous spread to the choroid plexus from reactivation of latent organisms from systemic organs rather than to reactivation of latent organisms within the brain itself. Furthermore, the high frequency of choroid plexitis offers the potential for CSF dissemination of this infection.

[Primary necrosis of the corpus callosum (Marchiafava-Bignami's disease): report of 5 cases]

The clinicopathological study of five autopsied cases of Marchiafava-Bignami disease is reported. The demyelination of the central portion of the corpus callosum is the major characteristics of the disease. In two cases the demyelination also involved the anterior and posterior commissures. There is a clear relationship to alcoholism and malnutrition in the cases reported in the present study.

Induced tolerance to Schistosoma mansoni antigens modulates periovular granuloma

Immunological tolerance to Schistosoma mansoni antigens induced by oral exposure of neonatal and adult mice to adult worm, soluble egg and polysaccharide antigens conducted to modulated periovular granuloma of infected mice. However the tolerance do not interfere in the infection. The estimative population and subpopulation of lymphocytes in the spleen of tolerized (not infected) animals do not differ from normal animals but Lyt 2.2 reactive lymphocytes to Schistosoma antigens was demonstrated in the tolerized animals.