Immunochemical and morphometric features of astrocyte reactivity vs. plaque location in Alzheimer's disease

The quantitative relationship between glial fibrillary acidic protein (GFAP) hyper-reactivity and -amyloid protein (AP) deposition was investigated by double immunoperoxidase labeling of hippocampal and entorhinal cortex sections from five Alzheimer´s disease (AD) cases and five age-matched controls. AP plaques, which were absent in controls, were found in all AD samples, without significant differences in number or perimeter according to their location among the regions studied. In contrast, the mean number of GFAP (+) cells was significantly greater in the hippocampus than in the entorhinal cortex from AD cases (49 vs.39). Although at lower values (30 vs. 20), predominance of astrocyte hyperplasia in hippocampus as compared with entorhinal cortex was also found in control samples. Concomitant astrocyte hypertrophy, as defined by surface density (Sv) values of GFAP-immunoreactive material exceeding those of control means, affected a similar proportion of cells in the hippocampus (73%) and the entorhinal cortex (74%) from AD cases. Since an increased number of GFAP (+) cells in the hippocampus was not accompanied by an increased number and/or perimeter of neighbouring plaques, such differential hyper-reactivity in samples from AD patients, as well as in those with normal aging, seems to depend partially on the regional location of the involved astrocyte.

Long-lasting astrocyte reaction to persistent Junin virus infection of rat cortical neurons.

Immunoperoxidase labeling was performed in histological sections from rat brain harvested during acute (10-30 days), clinically inapparent (90-270 days) and late (450-540 days) stages of Junin virus-induced neurological disease. In frontoparietal cortex, count of viral antigen (+) neurons peaked during the acute period (27.7+/-6.8), dropped within the intermediate (4.8+/-4.0 to 1.4+/-1.1) and increased (7.6+/-4.3) at the onset of the late neurological syndrome. In infected vs. control rats, the number of GFAP (+) astrocytes maximized during the acute stage (19+/-4 vs. 11+/-5), and from the end of the intermediate (27+/-5 vs. 21+/-5) up to the late (37+/-7 vs. 26+/-6) periods. In turn, surface density of GFAP (+) material in infected samples peaked at 0.196+/-0.066, while it failed to exceed 0.090+/-0.043 in controls. Both astrocyte hypertrophy relapsing into chronicity, as depicted by surface density, and astrocyte hyperplasia preceding the onset of the late neurological syndrome, support their pathogenic contribution to disease expression.

Theiler virus-GDVII strain (TMEV-GDVII) infection of cultured astrocytes. An image analysis of its effects on cell activation.

Our original aim was to determine whether dBcAMP-induced activation of cultured astrocytes affected the course of subsequent viral infection. After 2 h exposure of 2-day-old first subculture of mouse astrocytes to dBcAMP 1 mM, cell monolayers grown in glass coverslips of Leighton tubes were inoculated with 10(3) PFU of Theiler virus-GDVII strain (TMEV-GDVII). At 9 days post-infection (pi), viral infectivity persisted in supernatants from dBcAMP-treated cultures, but was no longer detectable in non-stimulated controls. The relatively spared astroglial monolayer at day 1 pi, hardly affected by progressive viral cytolytic effect, was chosen for immunolabeled cell count, whether by viral antigen or GFAP. To this end, 20 fields for each coverslip were digitalized at 250x final magnification. In dBcAMP treated cultures, viral antigen(+) cells were fewer and lower in percentage versus infected cultures lacking stimulation. As regards GFAP staining, stimulation or infection per se induced a greater number and percentage of labeled astrocytes. According to morphometric characterization, such increase was due to a greater number of process-bearing astrocytes. It may be concluded that, regardless of previous dBcAMP treatment, early TMEV-GDVII infection enhanced immunocytochemical and morphological differentiation in cultured astrocytes.

Theiler virus-GDVII strain (TMEV-GDVII) infection of cultured astrocytes. An image analysis of its effects on cell activation

Our original aim was to determine whether dBcAMP-induced activation of cultured astrocytes affected the course of subsequent viral infection. After 2 h exposure of 2-day-old first subculture of mouse astrocytes to dBcAMP 1 mM, cell monolayers grown in glass coverslips of Leighton tubes were inoculated with 10(3) PFU of Theiler virus-GDVII strain (TMEV-GDVII). At 9 days post-infection (pi), viral infectivity persisted in supernatants from dBcAMP-treated cultures, but was no longer detectable in non-stimulated controls. The relatively spared astroglial monolayer at day 1 pi, hardly affected by progressive viral cytolytic effect, was chosen for immunolabeled cell count, whether by viral antigen or GFAP. To this end, 20 fields for each coverslip were digitalized at 250x final magnification. In dBcAMP treated cultures, viral antigen(+) cells were fewer and lower in percentage versus infected cultures lacking stimulation. As regards GFAP staining, stimulation or infection per se induced a greater number and percentage of labeled astrocytes. According to morphometric characterization, such increase was due to a greater number of process-bearing astrocytes. It may be concluded that, regardless of previous dBcAMP treatment, early TMEV-GDVII infection enhanced immunocytochemical and morphological differentiation in cultured astrocytes.

Host selenium status selectively influences susceptibility to experimental viral myocarditis.

The purpose of the present work was to determine whether dietary selenium (Se) deficiency could influence the injurious effect of human viruses other than Coxsackie virus B3 (CVB3) on mouse heart. Weanling C3H/HeN mice were fed a Se-deficient or Se-adequate diet for 4 wk and then were inoculated intraperitoneally with one of the following viruses: Coxsackie virus B1 (CVB1), echovirus 9 (EV9), Coxsackie virus A9 (CVA9), or herpes simplex 1 (HSV1). Polio virus 1 (PV1) was employed as a negative control. Prior to inoculation, mean serum Se levels were 430 versus 61 ng/mL in adequate versus deficient mice, respectively. Ten days later, hearts were removed and processed by routine histological procedures. Cardiac lesions were scored according to the number and size of myocarditic foci. Significantly greater heart damage resulting from CVB1 and EV9 was observed in Se-deficient than in Se-adequate mice, and the Se status had no influence on CVA9-induced myocarditis. In contrast, heart damage caused by HSV1 was significantly milder in Se-deficient than in Se-adequate mice. Therefore, it may be concluded that the Se status of the murine host selectively influences the degree of viral-induced myocarditic lesions.

A quantitative approach to correlate astrocyte differentiation and phagocytic activity.

A triple staining procedure (PAP labeling for GFAP, PAS reaction for added yeast cells and hematoxylin for nuclear staining of the whole cell monolayer) had disclosed that Junin virus infection enhanced phagocytic activity by inducing greater astrocyte differentiation. Here, we resorted to a mathematical approach for simultaneous evaluation of astrocyte differentiation and potential phagocytosis. At light microscopy level, the total number of: a) PAS-stained yeast cells, b) PAS-stained yeast cells associated to GFAP-positive astrocytes, c) GFAP-positive astrocytes, and d) total number of GFAP-labeled and non-labeled astrocytes, were counted within the monolayer area delimited by a grid with a total area of 0.01 mm2. As the percentage of PAS-stained yeast cells associated to GFAP-positive astrocytes correlated significantly with the percentage of GFAP-positive astrocytes for the three yeast cell incubation times (24, 48 and 72 h), a mathematical approach involving a so-called beta parameter representing the percentage of differentiated astrocytes capable of taking up 50% of added yeast cells, was developed. Since beta value dropped along yeast cell incubation time, and more markedly in Junin-virus infected samples, a numerical value was thus available to assess enhanced phagocytic activity in astrocytes undergoing differentiation. Therefore, the application of a mathematical approach to cell monolayers subjected to current staining techniques, allows more objective analysis of data provided by cursory visualization at light microscopy level.

Immunocytochemical and morphological effects of short-term stimulation of cultured astrocytes.

Both image analysis at light microscopy level and ultrastructural characterization by transmission electron microscopy were employed to evaluate the differentiation stage in young cultured mouse astrocytes after 1-day exposure to dBcAMP, a chemical compound known to induce cell activation. The aim was to validate an experimental model of stimulated astrocytes preserving the properties of recently seeded cells, thus avoiding the overlapping effects of in vitro aging. Differentiated astrocytes, as evidenced by GFAP labeling by streptavidin-peroxidase, doubled their number in treated cultures (45%) versus controls (23%). In addition, a significant increase in process-bearing astrocytes (elongated and remified forms) to the detriment of immature polygonal astrocytes, was recorded. No noticeable changes were found in cell perimeter, but cell area displayed a significant reduction in labeled surface of astrocytes undergoing morphological differentiation. Concomitantly, electron microscopy showed that radially organized bundles of numerous intermediate filaments compatible with GFAP replaced the few scattered structures observed in control cultures. However, methodological caution is advisable as regards the relevance of this in vitro counterpart of in situ reactive astrocytes, since cell plasticity is recognized to depend on culture conditions. At any rate, present quantitative results demonstrate that GFAP-positive cell percentage and cell area measurement are adequate parameters of early immunocytochemical and morphological differentiation, respectively, and thus contribute to a better histometric characterization of an easily available substrate to discriminate the wide variety of factors involved in CNS response to injury.

Cell differentiation increases astrocyte phagocytic activity. A quantitative analysis of both GFAP labeling and PAS-stained yeast cells.

Since efficiency of phagocytic potential in activated astrocytes is still a subject of controversy, an attempt was made to quantify simultaneously phagocytic activity and astrocyte differentiation. Resorting to Junin virus, known to induce astrocyte activation, infected vs control samples of cultured rat astroglial cells were serially harvested up to day 12 post-inoculation (pi), and subjected to a triple staining procedure consisting in immunoperoxidase labeling of GFAP, periodic acid-Schiff (PAS) reaction in added baker's yeast cells and hematoxylin for nuclear staining of the whole cell monolayer. Adopting GFAP labeling as a specific marker of astrocyte differentiation, the immunoprecipitate development over time was measured. Direct calculation of the initial reaction rate was feasible given its linear behavior during the first 10 min, so that GFAP amount was regarded proportional to peroxidase activity. As determined by digital image analysis, mean optical density (MOD) values of GFAP in infected samples increased from 0.618 +/- 0.082 at day 1 pi to 0.825 +/- 0.125 at day 3, leveling off at 1.010 +/- 0.101 as from day 9, while control uninfected samples remained unchanged at roughly 0.6 during the entire observation period. In turn, phagocytosis was quantified by PAS staining densitometry, whose intensity varied according to wall degradation of yeast cells. MOD levels of PAS-stained phagocytized yeast cells were significantly lower (p < 0.05) in infected vs control cultures at 48 and 72 h following their addition to the astroglial monolayer. According to simultaneous quantification of two components of astrocyte response to viral infection, it is concluded that phagocytic activity increases with astrocyte differentiation.

Age-dependent morphological changes in dBcAMP-treated astrocytes.

Since changes in cell morphology are conspicuous features of astrocyte reaction, we resorted to an histometric approach to evaluate age influence on such morphological response to activating stimuli. To this end, first subculture of rat brain astrocytes at 1, 9 or 21 days in vitro (DIV) were treated during 2 hs with 1 mM of dBcAMP, a chemical compound known to induce cell differentiation. Following treatment, immunoperoxidase labeling of GFAP, specific marker of astrocyte activation, was carried out. Although total count of GFAP-positive cell foci was greater in treated samples in all times tested, when such cell foci were evaluated by image analysis, differences between perimeter/area ratios of such foci were only statistically significant at 1 DIV. It may be concluded that while dBcAMP effect is maintained despite astrocyte aging, the morphological pattern of response varies markedly along the observation period.

Glial fibrillary acidic protein (GFAP) immunochemical profile after junin virus infection of rat cultured astrocytes.

Cultured astrocytes derived from newborn rat brain were inoculated with Junin virus (JV) to characterize their response to infection by means of their glial fibrillary acidic protein (GFAP) immunochemical profile. Samples from 1 to 11 days post-inoculation (pi), as well as matched controls, were serially harvested for GFAP labeling by peroxidase-antiperoxidase (PAP) method. It was only at day 3 that significantly greater values of GFAP staining (P < 0.05) were disclosed by three complementary approaches: image analysis, ELISA and immunoblot densitometry. Since such increase was abolished by Triton X-100 treatment, soluble GFAP fraction appeared responsible for the early though transient enhancement of GFAP immunoreactivity that followed viral inoculation.

A brain soluble fraction inhibits synaptosomal membrane but not astrocyte ATPase activity.

Since a brain soluble fraction (peak II) is known to be able to inhibit synaptosomal membrane Na+, K(+)-ATPase activity, here we attempted to compare its effect on cellular and subcellular brain components such as synaptosomal and astrocytic membranes, as well as mitochondrial preparations. The difference between total and Mg(2+)-ATPase activity was noteworthy in synaptosomal membranes but proved unremarkable in astrocytic and mitochondrial preparations. Peak II highly inhibited total ATPase in synaptosomal membranes but failed to modify enzyme activity in astrocytic and mitochondrial preparations. Findings suggest cellular and subcellular specificity of peak II on brain ATPase activity.

Growth inhibition of herpes simplex virus-type 1 in calphostin C-treated astrocytes.

The aim was to evaluate the effects of calphostin C (CC), a protein kinase C inhibitor, on lytic herpes simplex virus-type 1 infection of cultured rat astrocytes. At 24 h postinjection, the cell culture receiving CC treatment at 50 nM concentration showed decreased cell detachment and retraction versus untreated infected controls; likewise, the infective virus yield was significantly lower in a dose-dependent manner. In contrast, image analysis failed to disclose differences in viral antigen immunolabeling at low drug concentrations thus suggesting that CC-induced inhibition of cytopathic effects and infectivity taken place through mechanisms not involving viral protein synthesis. Given the low dose required and the apparent lack of cytotoxic effects, present findings encourage additional studies on CC antiviral potential in the whole organism.

Neural spread of Junin virus in intraperitoneally inoculated rats.

On the basis of an already demonstrated Junín virus (JV) neural route after peripheral footpad infection of newborn rats, here we attempted to determine the viral pathway following intraperitoneal inoculation. As from the 2nd week post-infection, neurological disease developed reaching 84% mortality at 30 days. Immunoperoxidase labeling of viral antigen, concomitantly with infectivity assays and histological examination, was carried out in serially harvested samples. Whenever infectivity was detected, whether by viral rescue from coculture or by conventional isolation, viral antigen staining was achieved. Infective JV was present at threshold levels in spleen and liver from days 2 to 10, and in blood from days 5 to 15. In neural tissues, viral antigen was initially disclosed at day 5 in thoracic rachideal ganglia and related spinal cord segments. From day 7 thereafter, the entire spinal cord was involved; at this stage, first evidence of viral infection was found in brain stem, with subsequent spread to other encephalon structures at day 10. According to harvested samples, no significant differences were found in labeled cell percentages at thoracic vs cervical or lumbar levels of spinal cord. In contrasts, greater involvement of cerebral cortex versus brain stem, hippocampus or cerebellum was demonstrated shortly before death. Although JV antigen was overwhelmingly predominant in neurons, no morphological changes were apparent in such cells. Since rachideal spinal ganglia and spinal cord infection invariably preceded viral spread to encephalon, concomitantly with viral clearance from lymphoreticular organs and blood, a neural pathway seems warranted.

Histometric demonstration of periastrocytic fibronectin loss during herpes simplex virus infection.

Since Herpes simplex virus-type 1 (HSV-1) is liable to induce modifications and/or loss of immunoreactive fibronectin (FN) in cultured cells, our present goal was to determine whether such loss is attributable to FN binding impairment rather than cell detachment secondary to viral cytopathic effect. For this purpose, we resorted herein to an histometric approach for statistical evaluation of FN pattern in the course of HSV-1 infection of astroglial cell monolayers. The length of FN positive fibers was calculated by means of their tracing on a digitizer tablet; in the same field, cell nucleus count was performed. Recorded data allowed the calculation of an index as the ratio of the length of FN positive fibers over cell nucleus number. On comparing the indices between infected and control cultures, matricial FN loss was found in the former at 48 h post-inoculation, accompanied by cell fusion and retraction, though without cell detachment. A significant loss of FN was thus demonstrated as an event prior to severe cytopathic effect induced by viral infection.

Histometric demonstration of periastrocytic fibronectin loss during herpes simplex virus infection

Since Herpes simplex virus-type 1 (HSV-1) is liable to induce modifications and/or loss of immunoreactive fibronectin (FN) in cultured cells, our present goal was to determine whether such loss is attributable to FN binding impairment rather than cell detachment secondary to viral cytopathic effect. For this purpose, we resorted herein to an histometric approach for statistical evaluation of FN pattern in the course of HSV-1 infection of astroglial cell monolayers. The length of FN positive fibers was calculated by means of their tracing on a digitizer tablet; in the same field, cell nucleus count was performed. Recorded data allowed the calculation of an index as the ratio of the length of FN positive fibers over cell nucleus number. On comparing the indices between infected and control cultures, matricial FN loss was found in the former at 48 h post-inoculation, accompanied by cell fusion and retraction, though without cell detachment. A significant loss of FN was thus demonstrated as an event prior to severe cytopathic effect induced by viral infection.

Differential behaviour in pancreas and heart of two coxsackievirus B3 variants.

In order to characterize viral kinetics and pathogenic properties of two intratypic variants of coxsackievirus B type 3, Balb/c mice were intraperitoneally inoculated and serial samples harvested from days 2 to 28. Although both CB3o (amyocarditic) and CB3m (myocarditic) variants induced similar early infectivity titres in pancreas, only the latter led to severe acinar necrosis, followed in turn by patent viraemia and subsequent focal myocarditis. Nevertheless, when both variants were inoculated in cultured cardiac cells, neither infectivity nor cell death rate differed noticeable. Therefore, our findings indicate that overt myocarditis is not attributable to contrasting cardiomyocyte susceptibility to the tested variants but rather to prior viral events in pancreatic tissues.

Ultrastructural study of cell injury induced by coxsackievirus B3 in pancreatic and cardiac tissues.

Balb/c weanling mice were intraperitoneally inoculated with a myocarditic variant of coxsackievirus B3, with the aim of characterizing more thoroughly the features of virus-induced cell injury in pancreas and heart, as well as to compare ultrastructural alterations with histological and virological findings. During the first week post-infection (pi), all animals developed acinar pancreatitis, followed by focal myocarditis. At electron microscopy, acinar cells showed patent distortion, including marked loss of organelles and zymogen granules, together with gross dilatation of rough endoplasmic reticulum. Cardiac cells presented severe cytoskeletal changes, as myofibrillar collapse with a haphazard arrangement, concomitant with a decrease in myofibril number; besides, irregular pattern of nuclear chromatin and increased presence of swollen mitochondria were often observed. As the few initially detected lymphocytes tended to disappear in necrotic foci, there was an increase in fibroblast number concurrent with progressive scarring. Ultrastructural changes in both pancreas and heart correlated with local viral replication, suggesting that cell damage is attributable to direct viral action.